Halophiles space classified together slight (0.3–0.8 M NaCl), middle (0.8–3.4 M NaCl), and also extreme (>3.4 M NaCl) halophiles <37,43>.

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Gennaro Roberto Abbamondi, ... Barbara Nicolaus, in Quorum Sensing, 2019

2.1 Halophiles

The halophiles room a group of organisms v the capacity to prosper in hypersaline conditions. In this type of excessive environments, the salt concentrations are in overabundance of seawater and can additionally reach 20%–30% NaCl. Actually, Halophiles call for high salt concentration to prosper in these unusual habitats. The absence of liquid water, i beg your pardon is necessary for every living cell as metabolic reaction solvent, led this group of organisms to evolve various strategies to adapt to such too much conditions. Bacteria greatly counterbalance the osmotic pressure of these harsh settings by means of the manufacturing of high concentration of compatible solutes (small essential molecules), which room not associated in cabinet metabolism (amino, sugar, polyols, etc.). The build-up of high concentration of salt (KCl) within the cell is one more strategy, i m sorry is mainly embraced by Archaea and some halophilic anaerobic bacteria (Saum and Müller, 2008).

Hypersaline settings are often characterized by alkaliphilic parameters (high pH) and/or high temperatures; thus the halophilic strains could also be thermophiles and/or alkaliphiles (Montgomery et al., 2013; Pikuta et al., 2007).

It is described in the literature that QS might be associated in the procedures that regulate bacterial adaptation and growth in complicated environmental niches—that is the situation of hypersaline web page (Tommonaro et al., 2015). Amongst the halophiles, the main advancements in the investigation of QS resulted from the examine of the genus Halomonas. Llamas et al. (2005) analyzed the capacity of various moderately halophilic bacteria belonging come the genus Halomonas, to produce signal molecules connected in QS mechanism. Eleven exopolysaccharide-producing strains to be analyzed in total: H. Eurihalina (3 strains), H. Maura (4 strains), H. Ventosae (1 strain), and also H. Anticariensis (3 strains). The presence of N-acyl-homoserine lactones (AHLs) was detected by method of the indicator strains Agrobacterium tumefaciens NTL4 (pZLR4) and also Chromobacterium violaceum CV026 (Luo et al., 2001; McClean et al., 1997). AHL signal molecules were detected for all the experiment Halomonas strains; this finding let the writer speculate the QS may play a an essential role in harsh habitats, in details for biofilm formation and also exopolysaccharide (EPS) production. EPSs have actually a protective duty as a class to prevent desiccation, and in addition, castle facilitate cell-cell chemical communication (Decho, 2000). Part AHLs from H. Anticariens FP35(T) were also identified by means of fixed spectrometry (GC-MS and ESI tandem MS): N-butanoylhomoserine lactone (C4-HSL), N-hexanoylhomoserine lactone (C6-HSL), N-octanoylhomoserine lactone (C8-HSL), and also N-dodecanoylhomoserine lactone (C12-HSL) (Llamas et al., 2005).

The exact same research team deeply investigated QS in H. Anticariens FP35(T). They discovered that that QS system was created of luxR/luxI homologues: hanR (the transcriptional regulator gene) and hanI (the AHL synthase gene) (Tahrioui et al., 2011). The draft genome sequence of this gammaproteobacterium to be then reported on Genome Announcements (Tahrioui et al., 2013a). Tahrioui et al. (2013b) additionally performed a screening that AHLs production on 43 strains of the Halomonadaceae family. Also in this case, every the examined bacteria caused the indicator strain (for medium-to-long acyl chains). PCR and also DNA sequencing evaluation demonstrated the luxI homolog was current in many of the studied species, and also C6-HSL was detected together the most predominant AHL molecule (Tahrioui et al., 2013b). Halomonas smyrnensis AAD6 is a middle halophilic, exopolysaccharide-producing bacterium isolated native a saltern area in the Aegean region of Turkey (Poli et al., 2013). An AHL through an unsubstituted acyl side chain length of C16 was established in the dichloromethane extracts native stationary phase societies by means of LC-MS analysis. The writer hypothesized the the development phase–dependent manufacturing of the EPS might be regulation by QS (Abbamondi et al., 2016).

Halobacillus halophilus is a middle halophilic bacterium isolated indigenous a salt wetland on the coastline of Germany. That produces autoinducer-2 (AI-2) in a growth-phase dependency manner, highly dependent upon the existence of chloride ions. Much more specifically, the luxS homolog is upregulated by the anion concentration. It is feasible that QS plays an essential role in salt precipitation (chloride regulon), but additionally in cabinet motility (Averhoff and Müller, 2010; Sewald et al., 2007). The described examples of QS proof in halophiles room reported in Table 1.

HalophilesStrain(s)QS Molecule(s)/Genes IdentifiedBioreporter Strain(s)Modulated Activity/ActivitiesReference(s)H. Maura (4 strains), H. Ventosae (1 strain) and also H. Anticariensis (3 strais)H. Anticariens FP35(T)Halomonadaceae household (43 strains)Halomonas smyrnensis AAD6Halobacillus halophilus
N-acyl-homoserine lactones (AHLs)Agrobacterium tumefaciens NTL4 (pZLR4) and also Chromobacteriumviolaceum CV026Putative regulation the biofilm formation and exopolysaccharide (EPS) productionLlamas et al. (2005)
C4-HSL, C6-HSL, C8-HSL and also C12-HSL.hanR/hanI (luxR/luxI homologues)A. Tumefaciens NTL4 (pZLR4), C. Violaceum CV026Llamas et al. (2005) and Tahrioui et al. (2011)
C6-HSL(most primary AHL)LuxI homologA. Tumefaciens NTL4 (pZLR4)Tahrioui et al. (2013b)
C16-HSLA. Tumefaciens NTL4 (pCF218; pCF372)Putative regulation that EPS productionAbbamondi et al. (2016)
autoinducer-2 (AI-2)Modulation the salt precipitation (chloride regulon) and also cell motilityAverhoff and also Müller (2010) and also Sewald et al. (2007)

H.N. Chang, in comprehensive Biotechnology (Third Edition), 2011 Halobacteria (Bitop, Germany)

Lentzen and also Schwarz (2006) introduced a manufacturing of extremolyte ectoine making use of Halobacteria elongata. Halobacteria is a class of the Euryarchaeota uncovered in water saturation or almost saturated through salt, and they are also called halophiles, though this name is likewise used for various other organisms the live in somewhat less-concentrated salt water. Lock are common in most atmospheres where big amounts the salt, moisture, and organic material are available. The use of this bacteria eliminates the opportunity of contamination throughout the society because other common bacteria cannot live in this high salt condition, and downstream handling of any intracellular products from this bacteria is very easy since the cell walls have the right to be partly or completely broken by adding distilled water come the bacterial paste and placing the in a really low osmotic condition. This procedure will it is in a an excellent example that intracellular HCDC products.

Organisms the are capable of growing at high salt concentration achieve osmotic balance across the cabinet membrane utilizing low-molecular-weight polar compounds. Extremolytes method compatible solutes from extremophilic microorganisms. The ability of extremolytes come compensate osmotic pressure and also to stabilize macromolecules was studied extensively, and a model for their setting of activity of macromolecule stabilization was proposed. A proprietary commercial bioprocess, termed ‘bacterial milking‘, was developed for the industrial-scale production of the extremolyte ectoine. The cells are grown in MBRs come a high cell density and further handle to the process shown in Fig. 22.

A middle halophilic H. elongata ectoine producer is grown under high-salt problems (15%–20% w/v NaCl), and also the intracellularly collected ectoines space released by applying an osmotic down-shock, bring about the opening of mechanosensitive networks in the inside membrane that H. elongata. This is a fairly interesting part of the process because so-called ‘biomilking‘ releases only ectonine native the cells. The biomass is went back to the fermenter for the following round that fermentation, while the product equipment is further purified by electrodialysis, chromatography, filtration, evaporation, and crystallization. An ectoine bioprocess v an even higher productivity, based on the continuous fermentation of H. elongata, was developed recently. This constant ‘permanent milking‘ procedure is currently used by bitop AG because that the manufacturing of ectoines in metric ton scale. Because that the production of hydroxyectoine, a bioprocess making use of the Marinococcus strain M52 to be described. Alternatively, hydroxyectoine have the right to be developed with H. elongata by transforming the fermentation conditions in the bacter milking process.

Costantino Vetriani, in Encyclopedia the Biodiversity, 2001

II.C. Halophilic Archaea

The halophilic Archaea take place in environments characterized by high salinity. Salt-neutral lakes, saline soils, solar evaporation maritime salterns (areas wherein sea salt is produced), and subsurface haline deposits are among the most usual habitats for halophiles. Many of the halophilic Archaea room red or orange because of the visibility of carotenoid pigments in the cell envelope. Frequently, due to their abundance, they impart a red color to the brine. Alkaliphilic halophiles are discovered in soda lakes, i beg your pardon are very alkaline environments whose high pH (8 come >12) is because of high level of carbonate. Halophiles call for at least 1.5 M NaCl because that growth, and also optimal salt concentrations space usually in the selection of 2–4 M NaCl.

Neutrophilic and alkaliphilic halophiles both belong come the bespeak Halobacteriales. The members that the neutrophilic group, stood for by the genera Halobacterium, Halococcus, Haloarcula, and also Haloferax, grow optimally under problems of high magnesium and sodium concentration (0.5 and also 4.0 M, respectively) at pH ranging from 5 come 8. Alkaliphilc halophiles (genera Natronobacterium and Natronococcus) prosper optimally at low magnesium concentrations and pH of roughly 10.

Halophilic Archaea have advanced several physiological adaptations the permit their development in habitats v salt concentrations that cause cellular dehydration and also protein denaturation in other organisms. Halophilic Archaea such as Halobacterium resist high salt concentration by pumping big amounts that K+ native the environment into the cell such the the concentration that K+ within the cell is higher than the concentration the Na+ outside the cell. This mechanism enables Halobacterium to remain in hopeful water balance and avoid dehydration.

The halophilic Archaea room aerobic and grow heterotrophically utilizing carbohydrates, alcohols, essential acids, and also amino acids. Halobacterium types are normally aerobic but can flourish anaerobically in the existence of light. Under oxygen-limiting conditions and in the existence of light, Halobacterium inserts big amounts that a protein dubbed bacteriorhodopsin right into the cytoplasmic membrane. This purple pigment, i beg your pardon adsorbs irradiate strongly at around 570 nm, acts as a light-driven proton pump and leads come the facility of an electrochemical membrane potential. The equilibration have the right to be add by the generation that ATP. Thus, bacteriorhodopsin facilitates a special kind of photophosphorylation. The energy obtained by this mechanism complements that derived from aerobic substrate oxidation. Table III summarizes some qualities of the halophilic Archaea.

Order Genus SpeciesHabitatMorphologyPhysiological characteristics
 H. SalinarumSalted fish, hypersaline lakesAmino acids, phototrophic
 H. MediterraneiSalternsCarbohydrates
 H. DenitrificansSalternsNitrate respiration
 H. LacusprofundiDeep lake, AntarcticaCarbohydrates
 H. SodomenseDead SeaPhototrophic
 H. VallismortisDeath ValleyCarbohydrates
 H. MarismortuiDead SeaNitrate respiration
 H. MorrhuaeDead seaAmino acids, Nitrate respiration
 H. SaccharolyticusSalternsCarbohydrates
 N. GregoryiSoda lakesOrganic acids, ph 9.5–10
 N. OccultusSoda lakesAmino acids, ph 9.5–10
 N. AsiaticaSea sandNonpigmented, too much halophile

Ying Wang, ... Guo-Qiang Chen, in substantial Biotechnology (Third Edition), 2019 Microbial PHA/PHB manufacturing by Halomons spp.

Extremophiles resisting microbial air pollution are considered to be beneficial for low-cost production and thus are perfect to it is in employed in the NGIB.37,38 Halomons spp., a group of center halophilic bacteria isolated native a salt lake, the Aiding Lake in Xinjiang Province, China, can flourish under high PH and high salt concentration where the expansion of most ordinary microorganisms room inhibited.39 it was found that PHB have the right to be built up by numerous of these moderate halophiles. In fact, PHA build-up by halophiles was first reported in 1972,40 complied with by more and an ext studies on PHA synthesis by various halophiles including Haloferax, Haloarcula, Halobacterium et al.41–44 Haloferax mediterranei is one of the best-studied halophiles, creating 46 wt% PHA including PHBV ~ above glucose.39,45–49 Halomonas boliviensis was discovered to built up 81% PHB in 44 g L−1 cabinet dry weight (CDW) from various substrates such together glucose, xylose and also sucrose.50–54

Recent studies show that consistent and unsterile fermentation platform because that PHB production deserve to be developed based top top Halomons bluephagenesis TD01, a halophile i m sorry prefers to flourish optimally under 5%–6% NaCl (w/v) and pH 9.0.55 during a 14-day open up unsterile and continuous two-stage growth, cells were grown come 40 g L−1 cabinet dry weight containing 60% PHB there is no contamination during the an initial stage growth.55 Subsequently, cultures in the first fermentor were fed into the second fermentor comprise nitrogen-deficient glucose salt medium, resulting in an enhanced PHB buildup to 70%. Remarkably, the conversion ratio of glucose come PHB was amplified to end 50%.55

High consumptions ~ above freshwater and food sources are two significant concerns on commercial biotechnology. Food wastes quite than pure substrates have to be used as raw products for cabinet growth. Open and constant process is an extremely important for power saving and magnified effectiveness during the fermentation.56 together a process can considerably reduce expense of PHA production. An additional halophile Halomonas campaniensis LS21, also collected from Xinjiang Provence, China, was reported to be capable of utilizing blended substrates consist of of cellulose, proteins, fat and also starch separately or collectively for development on fabricated seawater. An open up and constant process use low-value substrates and artificial seawater was established based upon this strain, allowing a robust and long-lasting fermentation for 65 days without contamination with 70% PHB build-up in dried cell mass.57

In addition to PHB, various other PHA or related materials consisting of PHBV, P3HB4HB, biosurfactant proteins PhaR and also PhaP associated with intracellular PHA granules, have also been successfully synthesized by Halomons spp.58–60 Moreover, the production of P3HB4HB in Halomons spp. Has been scaled as much as a 5000 L fermentor because that low expense P3HB4HB manufacturing under open non-sterile and also fed-batch or consistent conditions.61 Sixty percent P(3HB-co-13.5 mol % 4HB) in 100 g/L CDW to be finally obtained after 36 h of expansion in the 5 m3 vessel.61

The domain Archaea includes the majority of presently well-known “extremophiles,” organisms that live at physics or chemistry extremes. Archaea significantly are gift discovered, however, in much less extreme species of environments, including the naval plankton, lakes, and sediments (e.g., DeLong, 1998; Vetriani et al., 1999). Diversity within the Archaea is presently less well understood than in the Bacteria and Eucarya due to the fact that the Archaea regularly require particular care come culture. Knowledge of exactly how to culture the Archaea has increased in recent years, and added habitats supporting their growth are being actively studied, for this reason the disparity in the numbers of various kinds of Archaea compared Bacteria should increasingly diminish. The Archaea consists currently of 3 kingdoms, the Euryarcheaota, the Crenarcheaota, and a provisional kingdom, the Korarchaeaota (Fig. 5).


Figure 5. Diversity and phylogenetic relationships amongst members the the domain Archaea. This maximum likelihood tree, based upon small-subunit rRNA, mirrors representatives of the Crenarchaeota (some excessive thermophiles and also some marine eco-friendly phylotypes) and of the Euryarchaeota (some extreme thermophiles, methanogens, halophiles, and marine eco-friendly phylotypes). The ecological phylotypes are suggested with acronyms and also numbers, with their eco-friendly origins designated. T. Maritima and also A. Pyrophilus form the bacter out-group. The scale represents the expected number of changes per sequence position. Check out Vetriani et al., 1999 for details and references. All set and noted by C. Vetriani, Rutgers University.

Two major types that bacteria, the methanogens and the too much halophiles, are had within the Euryarchaeota. Methanogens space bacteria that produce methane together an end-product of energy conversion reactions; they take place in a selection of strictly anaerobic habitats, such as sediments, sewage sludge digestors, the rumen the cattle, and the termite hindgut. CO2 and comparable compounds, methanol and other methyl-containing compounds, and also acetate are offered by different members that this team as substrates for methanogenesis, regularly with H2 together an electron donor. Methane, generally from methanogenic bacteria, is an essential greenhouse gas, accounting for possibly as much as a couple of percent of total primary production. Some methanogens, such together Methanococcus jannaschii, are hyperthermophiles. The extreme halophiles, represented by Halobacterium salinarum, room bacteria that need for survival and also growth the particularly high salt concentrations found in salt lakes and solar evaporation ponds. Other groups of Euryarchaeota incorporate a lineage of extremely acidophilic bacteria containing Thermoplasma and also Picrophilus, and two lineages that hyperthermophiles, stood for by Pyrococcus and Archaeoglobus (Fig. 4).

The Crenarchaeota contains a large and physiologically varied group the hyperthermophilic, sulfur-metabolizing bacteria from terrestrial and also marine hot springs and hydrothermal vents. Recently, number of Crenarchaeota (and Euryarchaeota) have been determined at the 16S rRNA level together members the the plankton in cold oceanic surface and deep waters, coastal sediments, lakes, and in association v animals, indicating that the Archaea are more cosmopolitan in their distribution than thought eariler (e.g., DeLong, 1998; Vetriani et al., 1999).

A 3rd kingdom that Archaea, the Korarchaeota, was created provisionally based on rRNA sequences acquired from samples the the Obsidian Pool hot spring in Yellowstone national Park and also distinct from those of various other Archaea (Pace, 1996). Make the efforts to carry these hyperthermophiles into pure culture are underway. The exploration of this third Archaean kingdom and also the recent discoveries of Archaea in cold, oxygenated habitats plainly indicate the the true diversity of Archaea is likely to much exceed that based on presently identified species and sequences obtained from eco-friendly samples. Implicitly in this newly evolving check out of Archaean phylogenetic diversity are substantially more comprehensive metabolic ability and more comprehensive ecological functions for this team of bacteria (DeLong, 1998; Vetriani et al., 1999).

Clemente Capasso, Mihail Barboiu, in Carbonic Anhydrases, 2019

22.4 Carbonic anhydrases indigenous extremophiles

Extremophiles room organisms i m sorry populate extreme niches, such together those characterized by an extremely hot or cold conditions, a high concentration of salt, and acid and also alkaline slots; or areas with toxicity waste, necessary solvents, heavy metals, high pressure, or various other habitats considered inhospitable because that life <44>. Considering the niches lock occupy, extremophiles have the right to be categorized into different groups: (1) thermophiles, organisms living at temperature ≥45°C, which are subdivided right into moderate thermophiles (45–70°C), excessive thermophiles cultivation optimally at temperature ≥70°C, (2) hyperthermophiles, organisms cultivation at really high temperatures (optimal temperature ≥80°C); (3) psychrophiles, organisms adjusted at low temperatures; (4) acidophiles and also alkaliphiles, organisms tolerating high acidic or an easy pH values, respectively; (5) barophiles, organisms that flourish under high pressure; and also (6) halophiles, organisms that tolerate high concentration of salt <44,45>. Extremophiles come indigenous Bacteria, Archaea, and also Eukarya domains; those from Bacteria and also Archaea are represented totally by microorganisms, vice versa, those within the Eukarya domain are largely algae-forming lichens, fungi, protozoa, and also organisms adjusted to live in ~ a an extremely low temperature (e.g., Antarctic fish). Intriguingly, the Tardigrades, microscopic invertebrates, forgive low and high temperatures, and also high sheep of radiation <46>.

To cope through these excessive habitats, the extremophiles have adjusted biomolecules and peculiar biochemical pathways. For example, the extremophiles are typified by very attractive biomolecules, dubbed “extremozymes,” which deserve to operate under the extreme conditions of temperatures, salinity, pH, pressure, and solvent problems in which their mesophilic counterparts might not endure <39,47>. These macromolecules are defined mainly through high security and task offering distinctive biotechnological advantages over the mesophilic enzymes (optimally active at 25–50°C), i m sorry are often not fine suited for the harsh reaction conditions required in industrial processes. As a result, the “extremozymes” are broadly used in biotechnological purposes. It is notable to psychic the sector of the “extremozymes” stood for by esterases/lipases, glycosidases, aldolases, nitrilases/amidases, phosphatases, racemases, the thermostable DNA polymerases, enzymes offered in the biofuel production or mining processes, and so on <47>.

Because numerous bacteria are extremely abundant in atmospheres that space hostile to all other forms of life, our groups focused the scientific attention on the existence of CAs in thermophilic and psychrophilic microorganisms. Their too much CAs are interesting candidates come be provided in industrial and medical applications, such together the postcombustion carbon capture procedure <29,48–59>, realization of fabricated lungs and also biosensors. Thus, this old superfamily the CA deserve to be considered as a biotechnological multitasking superfamily due to the fact that the CA classes are possibly able come fight both the rise of CO2 in the atmosphere created by the anthropogenic tasks and because that ameliorating the human health because of their biomedical interests. The extremophilic bacter CAs learned by us and other research groups are displayed in Table 22.1. The biochemical and also chemicophysical investigation of the too much bacterial CAs has led to the exploration of molecule properties, which make them various from those that the mesophilic counterpart allowing the use of the excessive bacterial CAs in biotechnological fields generally typified by conditions deleterious because that the enzyme task <38,39>. From the table, it is readily noticeable that all excessive CAs resulted good catalyst for the CO2 hydratase reaction through a kcat ranging from 104 to 106 s−1.

Table 22.1. List of carbonic anhydrases indigenous extremophilic bacteria v their kinetic parameters investigated by our various other research groups.

OrganismType that ExtremophileAcronymFamilykcat (s−1)kcat/KM (M−1 s−1)
Sulfurihydrogenibium yellowstonenseaExtreme thermophileSspCAα9.35 × 1051.1 × 108
Sulphurihydrogenibium azorensebExtreme thermophileSazCAα4.40 × 1063.5 × 108
Thermovibrio ammonificanscExtreme thermophileTaCAα1.60 × 1061.6 × 108
Persephonella marina EX-H1TdExtreme thermophilePmCAα3.2 × 1053.0 × 107
Methanobacterium thermoautotrophicumeModerate thermophileCabβ1.7 × 1045.9 × 106
Methanosarcina thermophilafModerate thermophileCamγ6.8 × 1043.1 × 106
Colwellia psychrerythraeagPsychrophileCpsCAγ6.0 × 1054.7 × 106
Pseudoalteromonas haloplanktishPsychrophilePhaCAγ1.4 × 1051.9 × 106
Nostoc communeiPsychrophileNcoCAγ9.5 × 1058.3 × 107
Pyrococcus horikoshiijHyperthermophilePhoCA

aFrom Refs. <60–62>;bFrom Refs. <63,64>;cFrom Ref. <65>;dFrom Ref. <66>;eFrom Ref. <67>;fFrom Ref. <68>;gFrom Refs. <69,70>;hFrom Refs. <71,72>;iFrom Refs. <73,74>;jFrom Ref. <75>.

This thing points out mainly on the recombinant extremophilic bacterial CAs, because that example, the SspCA and SazCA identified in the genome that the extreme thermophiles Sulfurihydrogenibium yellowstonense and Sulphurihydrogenibium azorense relenten the strategies embraced by our groups for making use of these too much SspCA in biotechnological applications. The biochemical and structural data on this CAs are generally well described and currently accessible in the literature <39,60–64,76–78>.


As their surname suggests, the archaebacteria room putatively a an ext ancient lineage. Their metabolism appears to have actually remained reasonably unchanged indigenous the early on days of an earth that short atmospheric oxygen. The archaebacteria incorporate three good subgroups: methane-producing, thermacidophilic, and also salt-tolerant prokaryotes. The very first two have their power in environments free of oxygen gas and produce wastes that perform not incorporate O2. Some, such together Thermoplasma and Sulfolobus, inhabit boiling-hot water choose the natural hot springs that Yellowstone national Park. The third group that archaebacteria, the halophiles, tolerate problems of too much salinity that room prohibitive come the expansion not just of larger organisms however of various other bacteria. Their genetic similarity, eco-friendly tolerance, and capacity to live in the lack of totally free oxygen gas suggest to one ancient history for the archaebacteria.

The eubacteria include all the rest, and the huge majority, that prokaryotes. Although very metabolically diverse, these bacteria include forms adept in ~ oxygenic photosynthesis, ammonia oxidation, ammonification, manganese oxidation and reduction, stole oxidation and also reduction, sulfur oxidation and also reduction, fermentation, and also nitrate respiration. The eubacteria own RNA sequences, lipid composition, and other traits that differentiate them indigenous the archaebacteria.

Intriguingly, however, archaebacterial RNAs show much more kinship to the RNAs of eukaryotes than they carry out to those of other bacteria. This is only among a slew of clues pointing to a shared ancestry in between archaebacteria and modern-day eukaryotes. Compounds lot like the histone proteins that type the packaging that chromosomes, for example, are discovered in Thermoplasma. yet there are probably even more features tying united state organisms do of eukaryotic cells come the eubacteria. Many striking space the reasonably narrow metabolic collection of every familiar big organisms, the oxidative respiration of every plants and also animals and fungi, and the photosynthesis that plants. The photosynthesis protoctists such together kelp and seaweed have specifically the same mechanism of food and also energy gathering as carry out the cyanobacteria. The highly circumscribed metabolism of every eukaryotes is well represented in the bacter world, a realm that evolved so numerous other type of metabolism.

Plants and also algae share oxygen-producing photosynthesis through cyanobacteria, and virtually all eukaryotes (animals, plants, fungi, and also protoctists) share your intracellular oxygen-using abilities v respiring bacteria. Plenty of other traits, such as fermentation of organic compounds into butyric acid and the oxidation of hydrogen sulfide to sulfate, remain difficult for united state selfdesignated “higher” organisms. (Perhaps “larger” is a more accurate term!)

The metabolic similarity of eukaryotes to a very few kinds of bacteria (prokaryotes), merged with the near lack of intermediate creates either life or in the fossil record, indicate an endosymbiotic, bacterial origin for eukaryotic bio cells. Other proof is even an ext provocative. The oxygen-using organelles, the membrane-bounded mitochondria, the are uncovered in almost all eukaryotic organisms space strikingly similar to respiring bacteria in the details of your chemistry. They directly reproduce as do respiring bacteria. Their own DNA is different from the DNA that the chromosomes in the nucleus of eukaryotic cells. These very same traits use to the plastids that algae and also plants, bacteria-sized photosynthetic cabinet inclusions. Castle too have their own DNA and their very own bacterial method of reproducing that is entirely different from the mitosis usual of eukaryotic cell division. The clincher, however, is the stretches the DNA in mitochondria and chloroplasts space statistically far more like follow me in the DNA of certain free-living develops of bacteria than they are favor the DNA that the cell in which castle reside. Indeed, no reasonable choices to the advancement of standard scale via bacterial endosymbioses of the forerunners come mitochondria and plastids exist, return the extent, the variety of symbiotic events, and the nature that the details continue to be a issue of clinical investigation and debate.

MARK O. WALDERHAUG, ... WOLFGANG EPSTEIN, in Ion transfer in Prokaryotes, 1987

A functions of K+ in Bacteria


K+ activates a variety of cell enzymes from pet cells, plant cells, and also bacteria (Evans and also Sorger, 1966; Suelter, 1970). There is nonspecific activation of many enzymes by ionic toughness independent of certain ions, but there is also details activation by K+. Ions of similar size, such together NH4+ and also Rb+, usually deserve to replace K+, while smaller monovalent cations with larger hydration shells such together Na+ and also Li+ often antagonize activation by K+. Activation of protein synthesis by K+ to be demonstrated by Ennis and also Lubin (1961) in researches of a K+-transport mutant of Escherichia coli. As cell K+ fell and Na+ rose, protein synthetic was significantly inhibited when RNA and DNA synthesis continued. Succeeding in vitro studies by Pestka (1972) showed that peptidyltransferase native E. Coli is especially activated by K+ end a wide selection of concentrations. Ammonium at short concentrations activates the enzyme yet is inhibitory at higher concentrations; Na+ and also Li+ inhibit. Hill plots indicated that a solitary K+ ion is compelled for activation. The peptidyltransferase from Bacillus stearothermophilus is also K+ caused (Fahnestock et al., 1974). Other enzymes especially activated by K+ include catabolic enzymes such as the serine deaminase (serine dehydratase) that E. Coli (Dupourque et al., 1966) and also the l-malate dehydrogenase the Lactobacillus arabinosus (Nossal, 1951), and biosynthetic enzyme such as the 3-hydroxyisopropyl malate dehydrogenase of Salmonella typhimurium (Burns et al., 1963), the aspartate kinase of Bacillus polymyxa (Paulus and Gray, 1964), the tryptophan synthase of Bacillus subtilis (Schwartz and also Bonner, 1964), the inosine monophosphate (IMP) dehydrogenase of Aerobacter aerogenes (Magasanik et al., 1957), and the porphobilinogen synthase in Rhodopseudomonas spheroides (Nandi et al., 1968). The variety of K+-dependent enzymes is probably bigger than reported because K+ is seldom rigorously excluded during enzyme isolation and assay.

The selection of cell K+ concentration in bacteria is large, native 18 mM in a freshwater thermophile (Searcy, 1976) come 4 M in Halobacterium halobium, a species requiring at least 2.5 M NaCl for growth (Christian and also Waltho, 1962; Kushner, 1978). However, the concentration that K+ required to activate enzyme is around 10 mM (Suelter, 1970), for this reason this need does no account because that the high levels of K+ discovered in most bacteria. Higher concentrations of K+ inhibit enzymes, probably a nonspecific ionic strength effect, but the concentrations that inhibit variety from below 0.1 M to greater than 1 M (Kushner, 1978; Pollard and also Wyn Jones, 1979). A striking exception is found in the enzyme of the too much halophile H. Halobium, all of which forgive high salt and some of i m sorry require more than 2 M K+ for optimum activity and security (Lanyi, 1974; Kushner, 1978). Enzyme activation by ions that have the right to substitute for K+ is more than likely not of organic significance, since Rb+ and Cs+ are rare cations, and also at least some bacter K+ transport equipment discriminate against Rb+ and Cs+. The various other potentially activating ion, NH4+, appears to be existing at rather low concentrations in every cells. Thus, activation of enzymes by K+ is a duty that cannot usually be replaced by other ions and also is satisfied by K+ concentrations listed below those usual of bacteria.


The osmotic task of intracellular K+ counts on the form of anion with which K+ is associated. Cell K+ have the right to be put into two classes: that associated with solved anions in the cell, and that associated with small, diffusible, anions. The K+ associated with fixed, macromolecular anions such as main point acids and also proteins has actually low osmotic activity, only about 10% the its osmotic activity in salts such as KCl, based upon osmotic research studies of synthetic ionic polymers (Alexand rowicz, 1962). The remaining K+, linked with low molecular weight anionic compounds, has actually high osmotic activity comparable to the of analogous mixtures in totally free solution. The quantity of K+ connected with resolved anions have the right to be approximated by measuring the K+ retained after cell made permeable to tiny molecules are washed v distilled water, or after undamaged cells room shocked with distilled water, i beg your pardon produces transient nonspecific permeability to little molecules (Epstein and also Schultz, 1965; Tsapis and also Kepes, 1977). All cell K+ is easily removed by exchange with another monovalent cation (Epstein and Schultz, 1965), indicating that a negligible portion of K+ is associated with binding website of high affinity and also specificity.

The osmotic dependence of cell K+ and osmotic manage of K+ activities are the key lines of proof implicating this cation in osmotic regulation. In bacteria, cabinet osmolarity is preserved at a level over that of the medium (Knaysi, 1951). This distinction in osmotic pressure, called the turgor pressure, shows up to be crucial for development of bacteria and also of various other cells with walls, such as plants and also fungi. The solid correlation in between medium osmolarity and cell K+ demonstrated in some varieties (Christian, 1955; Epstein and also Schultz, 1965; Richey et al., 1987) argues this ion is built up in part to maintain interior osmolarity in ~ a fairly fixed level over that outside. The correlation of cell K+ through the maximum osmolarity tolerated by a given varieties is evidence for an osmotic role of this cation (Christian and also Waltho, 1960). Steps of the collapse press of gas vacuoles to determine turgor in two species of cyanobacteria has presented that buildup of K+ and associated anions have the right to account quantitatively for the changes in turgor push that occur after raising the osmolarity of the tool (Allison and Walsby, 1981; Reed and also Walsby, 1985). The K+ accumulated must be accompanied by one equal variety of anionic charges. In several species about a quarter of the anions are well-known to be stood for by glutamate (Measures, 1975; Richey et al., 1987), yet the other anions continue to be to it is in identified.

The most straight evidence supporting an osmotic function of K+ is the regulate of K+ movements by osmotic changes. Reduce turgor push by enhancing the osmolarity the the medium, a procedure below referred to together upshock, stimulates K+ uptake. Downshock, the opposite adjust in i m sorry turgor is increased by reducing the osmolarity the the medium, leads to K+ efflux. When there is a large, rapid reduction in outside osmolality, the boost in turgor might be higher than have the right to be withstood by the cabinet envelope. As a result, cells undergo osmotic shock, in which there is transient failure of envelope integrity with nonspecific lose of tiny molecules, periplasmic proteins, and even some intracellular protein (Kundig et al., 1966; Heppel, 1969; Perlin and also Lerner, 1981). The certain loss of K+ produced by a gentle increase in turgor is proof for a mechanism to reduce internal osmolarity by the managed loss that K+ and also presumably that the diffusible anions linked with that (Meury et al., 1985).


The K+ gradient is rarely supplied by bacteria together an energy resource to drive transport. The high concentration that K+ in the cell, representing a force driving K+ efflux, is opposed by the membrane potential (Δψ), interior negative, which cd driver cation influx. Because of this this gradient is valuable only because that the electrically neutral exchange the K+ for one more cation, and also then just when outside K+ is low. These problems are the needs of an ammonium and also methylammonium uptake mechanism in E. Coli (Jayakumar et al., 1985) and also apparently also for a similar system in Methanospirillum hungati (Sprott et al., 1984). In every case, ammonium (or methylammonium) absorb is dramatically inhibited through elevated concentrations of exterior K+ and also is associated 1:1 v the efflux of K+. Skulachev and also co-workers (Skulachev, 1978; Arshavsky et al., 1981) have argued the K+ gradient and that for Na+ might serve as an energy buffer once the proton-motive force (PMF) is low. However, the quantity of power in the K+ gradient of many bacteria is small. For E. Coli in tool containing 0.1 mM K+ it to represent the tantamount of about 30 sec of fermentative line of glucose in ~ 37°C. The amount is much larger for organisms such as H. Halobium, who K+ pools are practically 20 times as large, but only if outside K+ is very low.

Transport systems that exchange K+ because that protons have been defined in countless bacteria, yet the physiological functions of together K+/H+ antiporters room not yet firmly established. It has been postulated the antiporters aid maintain internal pH by pump in protons when outside pH is high (Brey et al., 1978; Nakamura et al., 1984), or usage the K+ gradient to aid buffer cabinet pH ~ above sudden alters of internal or exterior pH (for review see Booth, 1985). A K+/H+ antiporter could serve come expel K+ indigenous cells and also organelles through a high membrane potential to prevent being flooded v cations entering progressively through leak pathways (Mitchell, 1966).

4 internal K+ as REGULATOR

A regulatory function for cabinet K+ has been suggested to define the regulate of enzyme activity, carry activity, and also gene expression which is dependence on the osmolarity that the tool (Epstein, 1986; Sutherland et al., 1986). An increase in cell K+ is proposed to be the primary event in adapting to media of higher osmolality. Subsequently, the boosted cell K+ (or elevated ionic strength) acts come control tasks responsible for the accumulation of other osmotic solutes, such as betaine, trehalose, and sucrose, whose accumulation spares part of the need for extr K+ and provides high internal osmolarity without extreme internal ionic strength. Increased cell K+ has actually been implicated as regulating expression of details genes in Rhizobium (Gober and also Kashket, 1987).

Giuseppe Graziano, Antonello Merlino, in Biochimica et Biophysica Acta (BBA) - Proteins and also Proteomics, 2014

2 Halophilic and halotolerant proteins

Halophiles are (micro)organisms that require salt because that growth. Castle are adjusted to live in high salinity atmospheres (> 0.2 M NaCl) and also are resistant to the impact of osmotic stress. They encompass aerobic or anaerobic bacteria, cyanobacteria, archaea, protozoa, fungi, algae and multicellular eukaryotes. Slight halophiles flourish optimally in ~ 0.2–0.85 M (2–5%) NaCl, while moderate halophiles at 0.85–3.4 M (5–20%) NaCl and extreme halophiles at 3.4–5.1 M (20–30%) NaCl <17–19>. Our anthropocentric point of view caused the classification of halophilic (micro)organisms together extremophiles <20>.

Proteins are called halophilic once they space isolated from halophiles. Halophilic proteins commonly need high NaCl concentrations to survive, halophilic enzymes require salt because that catalytic activity.

There are also numerous proteins which tolerate high salt concentrations, yet are not isolated native halophilic sources. This proteins are called halotolerant. Halotolerant enzymes remain active over a broad variety of NaCl concentration, without any particular salt dependency <21,22>.

Several independent studies have presented that halophilic and halotolerant proteins are able to work-related in problems where ordinary enzymes may accumulation or shed enzymatic task <21>. The peculiar capability of these proteins to be stable and to duty in this extreme atmospheres has been pertained to a number of different features. Main efforts to specify the structural functions of a protein that identify its resistance to this harsh environment are summarized below. In the following sections, sequence comparison in ~ genome and proteome levels and structural comparison in between halophilic proteins and their mesophilic counterparts will certainly be described, through the target to define the essential feature of a protein to cope v high salinity environment. Finally, a thermodynamic model for rationalizing halophilic protein stabilization at high salt concentration is discussed.

Vijay Kumar, ... Dharam Singh, in worldwide Journal of biological Macromolecules, 2020

4.1 PHA production opportunity in unsterile fermentation condition

Halophiles can thrive in a medium containing high NaCl concentration, thus, enabling unsterile fermentation problems with lower energy and also investments in addition to effortless restore of PHA <47,67>. These functions make halophiles immensely an useful for next-generation industrial biotechnology <93>. Amongst many unsterile bioprocess studies using salt-loving microbes, Tan et al. Had actually designed a continuous and unsterile bioprocess making use of Halomonas sp. <57>. The process yields high cell development up to 80 g/L with in its entirety PHB content of 80% come its dry cell load employing glucose together carbon source. The bioprocess in two-stage fermentation permits the average biomass production up come 40 g/L and also 60–70% the PHB accumulation <57>. This strategy an extremely effectively reduced down the sterilization price and likewise attained high cell thickness during fermentation. In an additional study, a fed-batch bioprocess utilizing Halogranum amylolyticum on glucose medium produced 29 g/L that biomass and 14 g/L of PHB-HV accumulation with 20% the 3-hydroxyvalerate <67>. A comparable study employing a novel halotolerant Bacillus sp. Ended 2.02 g/L of PHB-HV manufacturing with 48% the 3-hydroxyvalerate making use of glucose as a carbon source <59>. However, the use of glucose as a carbon source remains a difficulty to the as whole production cost.

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Similar to saline niches microbes, the marine and also thermophiles bacteria also possess the advantages of PHA manufacturing in unsterile condition. The filtered sea water have the right to be used for culture medium, thereby, reduce sterilization expense to make commercial scale manufacturing feasible <70,107>. In situation of thermophiles, the sterilization cost can be decreased due to high-temperature fermentation v a lesser possibility of contamination. The additional edge the thermophiles over halophiles and marine microbes is the there is no have to use high salt concentration in fermentation media, but the disadvantage is the maintenance of greater temperature throughout the entirety process. PHA developing microbes indigenous polar or low-temperature niches have opportunities in ax of finding novelty in PHA compositions. However, bioprocess advancement using psychrophiles have the right to be a little costlier because of the need of low-temperature maintenance.