Salt Stress-Induced Changes in the Transcriptome, Compatible Solutes, and Membrane Lipids in the Facultatively Phototrophic Bacterium Rhodobacter sphaeroides

ABSTRACTResponses to NaCl stress were investigated in phototrophically grownAlphaproteobacterium Rhodobacter sphaeroidesby transcriptome profiling, mutational analysis, and measurements of compatible solutes and membrane phospholipids. After exposure to salt stress, genes encoding two putative glycine betaine uptake systems,proVWXandbetS, were highly upregulated. Mutational analysis revealed that BetS, not ProVWX, was the primary transporter of this compatible solute. Upon the addition of salt, exogenous glycine betaine was taken up rapidly, and maximal intracellular levels were reached within minutes. In contrast, synthesis of another important compatible solute inR. sphaeroides, trehalose, increased slowly following salt stress, reaching maximal levels only after several hours. This accumulation pattern was consistent with the more gradual increase in salt-induced transcription of the trehalose biosynthesis operonotsBA. Several genes encoding putative transcription factors were highly induced by salt stress. Multiple copies of one of these factors,crpO(RSP1275), whose product is a member of the cyclic AMP receptor protein/fumarate and nitrate reduction regulator (CRP/FNR) family, improved NaCl tolerance. WhencrpOwas provided in multicopy, expression of genes for synthesis or transport of compatible solutes was unaltered, but the membrane phospholipid composition became biased toward that found in salt-stressed cells. Collectively, this study characterized transcriptional responses to salt stress, correlated changes in transcription with compatible solute accumulation rates, identified the main glycine betaine transporter and trehalose synthase, characterized salt-induced changes in phospholipid composition, and uncovered a transcription factor associated with changes in phospholipids. These findings set the stage for deciphering the salt stress-responsive regulatory network inR. sphaeroides.

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Investigations of Dimethylglycine, Glycine Betaine, and Ectoine Uptake by a Betaine-Carnitine-Choline Transporter Family Transporter with Diverse Substrate Specificity in Vibrio Species

Journal of Bacteriology ◽

10.1128/jb.00314-20 ◽

2020 ◽

Vol 202 (24) ◽

Author(s):

Gwendolyn J. Gregory ◽

Anirudha Dutta ◽

Vijay Parashar ◽

E. Fidelma Boyd

Keyword(s):

Amino Acid ◽

Glycine Betaine ◽

Vibrio Parahaemolyticus ◽

Compatible Solutes ◽

Binding Pocket ◽

Compatible Solute ◽

Amino Acid Residues ◽

Choline Transporter ◽

Content Type ◽

Highly Effective

ABSTRACT Fluctuations in osmolarity are one of the most prevalent stresses to which bacteria must adapt, both hypo- and hyperosmotic conditions. Most bacteria cope with high osmolarity by accumulating compatible solutes (osmolytes) in the cytoplasm to maintain the turgor pressure of the cell. Vibrio parahaemolyticus, a halophile, utilizes at least six compatible solute transporters for the uptake of osmolytes: two ABC family ProU transporters and four betaine-carnitine-choline transporter (BCCT) family transporters. The full range of compatible solutes transported by this species has yet to be determined. Using an osmolyte phenotypic microarray plate for growth analyses, we expanded the known osmolytes used by V. parahaemolyticus to include N,N-dimethylglycine (DMG), among others. Growth pattern analysis of four triple-bccT mutants, possessing only one functional BCCT, indicated that BccT1 (VP1456), BccT2 (VP1723), and BccT3 (VP1905) transported DMG. BccT1 was unusual in that it could take up both compounds with methylated head groups (glycine betaine [GB], choline, and DMG) and cyclic compounds (ectoine and proline). Bioinformatics analysis identified the four coordinating amino acid residues for GB in the BccT1 protein. In silico modeling analysis demonstrated that GB, DMG, and ectoine docked in the same binding pocket in BccT1. Using site-directed mutagenesis, we showed that a strain with all four residues mutated resulted in the loss of uptake of GB, DMG, and ectoine. We showed that three of the four residues were essential for ectoine uptake, whereas only one of the residues was important for GB uptake. Overall, we have demonstrated that DMG is a highly effective compatible solute for Vibrio species and have elucidated the amino acid residues in BccT1 that are important for the coordination of GB, DMG, and ectoine transport. IMPORTANCE Vibrio parahaemolyticus possesses at least six osmolyte transporters, which allow the bacterium to adapt to high-salinity conditions. In this study, we identified several additional osmolytes that were utilized by V. parahaemolyticus. We demonstrated that the compound DMG, which is present in the marine environment, was a highly effective osmolyte for Vibrio species. We determined that DMG is transported via BCCT family carriers, which have not been shown previously to take up this compound. BccT1 was a carrier for GB, DMG, and ectoine, and we identified the amino acid residues essential for the coordination of these compounds. The data suggest that for BccT1, GB is more easily accommodated than ectoine in the transporter binding pocket.

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Conserved ABC Transport System Regulated by the General Stress Response Pathways of Alpha- and Gammaproteobacteria

Journal of Bacteriology ◽

10.1128/jb.00746-16 ◽

2016 ◽

Vol 199 (5) ◽

Cited By ~ 4

Author(s):

Julien Herrou ◽

Jonathan W. Willett ◽

Daniel M. Czyż ◽

Gyorgy Babnigg ◽

Youngchang Kim ◽

...

Keyword(s):

Transport System ◽

Brucella Abortus ◽

Quaternary Ammonium ◽

Sigma Factor ◽

Glycine Betaine ◽

Chronic Infection ◽

Compatible Solutes ◽

Compatible Solute ◽

Periplasmic Binding Protein ◽

Content Type

ABSTRACT Brucella abortus σE1 is an EcfG family sigma factor that regulates the transcription of dozens of genes in response to diverse stress conditions and is required for maintenance of chronic infection in a mouse model. A putative ATP-binding cassette transporter operon, bab1_0223-bab1_0226, is among the most highly activated gene sets in the σE1 regulon. The proteins encoded by the operon resemble quaternary ammonium-compatible solute importers but are most similar in sequence to the broadly conserved YehZYXW system, which remains largely uncharacterized. Transcription of yehZYXW is activated by the general stress sigma factor σS in Enterobacteriaceae, which suggests a functional role for this transport system in bacterial stress response across the classes Alphaproteobacteria and Gammaproteobacteria. We present evidence that B. abortus YehZYXW does not function as an importer of known compatible solutes under physiological conditions and does not contribute to the virulence defect of a σE1-null strain. The sole in vitro phenotype associated with genetic disruption of this putative transport system is reduced growth in the presence of high Li+ ion concentrations. A crystal structure of B. abortus YehZ revealed a class II periplasmic binding protein fold with significant structural homology to Archaeoglobus fulgidus ProX, which binds glycine betaine. However, the structure of the YehZ ligand-binding pocket is incompatible with high-affinity binding to glycine betaine. This is consistent with weak measured binding of YehZ to glycine betaine and related compatible solutes. We conclude that YehZYXW is a conserved, stress-regulated transport system that is phylogenetically and functionally distinct from quaternary ammonium-compatible solute importers. IMPORTANCE Brucella abortus σE1 regulates transcription in response to stressors encountered in its mammalian host and is necessary for maintenance of chronic infection in a mouse model. The functions of the majority of genes regulated by σE1 remain undefined. We present a functional/structural analysis of a conserved putative membrane transport system (YehZYXW) whose expression is strongly activated by σE1. Though annotated as a quaternary ammonium osmolyte uptake system, experimental physiological studies and measured ligand-binding properties of the periplasmic binding protein (PBP), YehZ, are inconsistent with this function. A crystal structure of B. abortus YehZ provides molecular insight into differences between bona fide quaternary ammonium osmolyte importers and YehZ-related proteins, which form a distinct phylogenetic and functional group of PBPs.

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Freshwater Cyanobacterium Synechococcus elongatus PCC 7942 Adapts to an Environment with Salt Stress via Ion-Induced Enzymatic Balance of Compatible Solutes

Applied and Environmental Microbiology ◽

10.1128/aem.02904-19 ◽

2020 ◽

Vol 86 (7) ◽

Cited By ~ 1

Author(s):

Yajing Liang ◽

Mingyi Zhang ◽

Min Wang ◽

Wei Zhang ◽

Cuncun Qiao ◽

...

Keyword(s):

Salt Stress ◽

De Novo ◽

Compatible Solutes ◽

Synechococcus Elongatus ◽

Compatible Solute ◽

Sucrose Accumulation ◽

Content Type ◽

Freshwater Cyanobacterium ◽

Synergistic Modulation ◽

Pcc 7942

ABSTRACT Salinity is one of the most important abiotic factors in various natural habitats of microbes. Cyanobacteria are the most widely distributed family of photosynthetic microorganisms in environments with fluctuating salinity. In response to salt stress, many cyanobacteria de novo synthesize compatible solutes to maintain osmotic balance in the cell. However, the regulation of intracellular accumulation of these compounds is still not well understood. The freshwater cyanobacterium Synechococcus elongatus PCC 7942 (Syn7942) exclusively accumulates sucrose as a compatible solute upon salt stress and is thus an ideal model microorganism for studying the metabolism of compatible solute dynamics. Here, we focused on elucidating the regulatory mechanisms involved in salt-induced sucrose accumulation in Syn7942. Using a series of physiological and biochemical experiments, we showed that the ionic effect of salt stress plays an important role in inducing sucrose synthesis, whereby elevated ion concentration directly activates the sucrose-synthesizing enzyme sucrose-phosphate synthase and simultaneously inhibits the sucrose-degrading enzyme invertase, resulting in a rapid sucrose accumulation. Thus, we propose a novel mechanism for cyanobacterial adaption to salt stress and fluctuating salinity, i.e., the ion-induced synergistic modulation of the enzymes synthesizing and degrading compatible solutes. These findings greatly enhance our current understanding of microbial adaptation to salt. IMPORTANCE Most microbes de novo synthesize compatible solutes for adaptation to salt stress or fluctuating salinity environments. However, to date, one of the core questions involved in these physiological processes, i.e., the regulation of salt-induced compatible solute biosynthesis, is still not well understood. Here, this issue was systematically investigated by employing the model freshwater cyanobacterium Synechococcus elongatus PCC 7942. A novel mechanism for cyanobacterial adaption to salt stress and fluctuating salinity, i.e., the ion-induced synergistic modulation of key synthesizing and degrading enzymes of compatible solutes, is proposed. Because the ion-induced activation/inhibition of enzymes is a fast and efficient process, it may represent a common strategy of microbes for adaptation to environments with fluctuating salinity.

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Humectant Permeability Influences Growth and Compatible Solute Uptake by Staphylococcus aureus Subjected to Osmotic Stress

Journal of Food Protection ◽

10.4315/0362-028x-65.6.1008 ◽

2002 ◽

Vol 65 (6) ◽

pp. 1008-1015 ◽

Cited By ~ 18

Author(s):

ODDUR VILHELMSSON ◽

KAREN J. MILLER

Keyword(s):

Staphylococcus Aureus ◽

Sodium Chloride ◽

Water Activity ◽

Glycine Betaine ◽

Compatible Solutes ◽

Foodborne Pathogen ◽

Compatible Solute ◽

Solute Uptake ◽

Stressed Cells ◽

Carnitine Uptake

The effects of different humectants (sodium chloride, sucrose, and glycerol) on the growth of and compatible solute (glycine betaine, proline, and carnitine) uptake by the osmotolerant foodborne pathogen Staphylococcus aureus were investigated. While growth in the presence of the impermeant humectants sodium chloride and sucrose induced the accumulation of proline and glycine betaine by cells, growth in the presence of the permeant humectant glycerol did not. When compatible solutes were omitted from low-water-activity media, growth was very poor in the presence of impermeant humectants. In contrast, the addition of compatible solutes had essentially no effect on growth when cells were grown in low-water-activity media containing glycerol as the humectant. Carnitine was found to accumulate to high intracellular levels in osmotically stressed cells when proline and glycine betaine were absent, making it a potentially important compatible solute for this organism.

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Identification of a Salt-Induced Primary Transporter for Glycine Betaine in the Methanogen Methanosarcina mazei Gö1

Applied and Environmental Microbiology ◽

10.1128/aem.68.5.2133-2139.2002 ◽

2002 ◽

Vol 68 (5) ◽

pp. 2133-2139 ◽

Cited By ~ 19

Author(s):

M. Roeßler ◽

K. Pflüger ◽

H. Flach ◽

T. Lienard ◽

G. Gottschalk ◽

...

Keyword(s):

Glycine Betaine ◽

Northern Blot Analysis ◽

Compatible Solutes ◽

Gene Organization ◽

Compatible Solute ◽

Salt Adaptation ◽

Methanosarcina Mazei ◽

Transport Studies ◽

Uptake Activity ◽

Transport Device

ABSTRACT The salt adaptation of the methanogenic archaeon Methanosarcina mazei Gö1 was studied at the physiological and molecular levels. The freshwater organism M. mazei Gö1 was able to adapt to salt concentrations up to 1 M, and the addition of the compatible solute glycine betaine to the growth medium facilitated adaptation to higher salt concentrations. Transport studies with cell suspensions revealed a salt-induced glycine betaine uptake activity in M. mazei Gö1, and inhibitor studies argue for a primary transport device. Analysis of the genome of M. mazei Gö1 identified a homolog of known primary glycine betaine transporters. This gene cluster was designated Ota (osmoprotectant transporter A). Its sequence and gene organization are very similar to those of the glycine betaine transporter OpuA of Bacillus subtilis. Northern blot analysis of otaC revealed a salt-dependent transcription of this gene. Ota is the first identified salt-induced transporter for compatible solutes in Archaea.

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CosR is a repressor of compatible solute biosynthesis and transporter systems

10.1101/845297 ◽

2019 ◽

Author(s):

Gwendolyn J. Gregory ◽

Daniel P. Morreale ◽

E. Fidelma Boyd

Keyword(s):

Glycine Betaine ◽

Vibrio Parahaemolyticus ◽

Turgor Pressure ◽

Regulatory Region ◽

Compatible Solutes ◽

Compatible Solute ◽

Negative Regulator ◽

Low Salinity ◽

Transporter Systems ◽

Ectoine Biosynthesis

AbstractBacteria accumulate small, organic compounds, called compatible solutes, via uptake from the environment or biosynthesis from available precursors to maintain the turgor pressure of the cell in response to osmotic stress. Vibrio parahaemolyticus has biosynthesis pathways for the compatible solutes ectoine (ectABCasp_ect) and glycine betaine (betIBAproXWV), four betaine-carnitine-choline transporters (bcct1-bcct4) and a second ProU transporter (proVWX). Most of these systems are induced in high salt. CosR, a MarR-type regulator, which is divergently transcribed from bcct3, was previously shown to be a direct repressor of ectABCasp_ect in Vibrio species. In this study, we investigated the role of CosR in glycine betaine biosynthesis and compatible solute transporter gene regulation. Expression analyses demonstrated that betIBAproXWV, bcct1, bcct3, and proVWX are repressed in low salinity. Examination of an in-frame cosR deletion mutant shows induced expression of these systems in the mutant at low salinity compared to wild-type. DNA binding assays demonstrate that purified CosR binds directly to the regulatory region of each system. In Escherichia coli GFP reporter assays, we demonstrate that CosR directly represses transcription of betIBAproXWV, bcct3, and proVWX. Similar to V. harveyi, we show betIBAproXWV is positively regulated by the LuxR homolog OpaR. Bioinformatics analysis demonstrates that CosR is widespread within the genus, present in over 50 species. In several species, the cosR homolog was clustered with the betIBAproXWV operon, which again suggests the importance of this regulator in glycine betaine biosynthesis. Incidentally, in four Aliivibrio species that contain ectoine biosynthesis genes, we identified another MarR-type regulator, ectR, clustered with these genes, which suggests the presence of a novel ectoine regulator. Homologs of EctR in this genomic context were present in A. fischeri, A. finisterrensis, A. sifiae and A. wodanis.ImportanceVibrio parahaemolyticus can accumulate compatible solutes via biosynthesis and transport, which allow the cell to survive in high salinity conditions. There is little need for compatible solutes under low salinity conditions, and biosynthesis and transporter systems are repressed. However, the mechanism of this repression is not fully elucidated. CosR plays a major role in the repression of multiple compatible solute systems in V. parahaemolyticus as a direct negative regulator of ectoine and glycine betaine biosynthesis systems and four transporters. Homology analysis suggests that CosR functions in this manner in many other Vibrio species. In Aliivibrio species, we identified a new MarR family regulator EctR that clusters with the ectoine biosynthesis genes.

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Quorum Sensing Regulators AphA and OpaR Control Expression of the Operon Responsible for Biosynthesis of the Compatible Solute Ectoine

Applied and Environmental Microbiology ◽

10.1128/aem.01543-19 ◽

2019 ◽

Vol 85 (22) ◽

Cited By ~ 4

Author(s):

Gwendolyn J. Gregory ◽

Daniel P. Morreale ◽

Megan R. Carpenter ◽

Sai S. Kalburge ◽

E. Fidelma Boyd

Keyword(s):

Quorum Sensing ◽

Vibrio Parahaemolyticus ◽

De Novo ◽

Turgor Pressure ◽

Compatible Solutes ◽

Compatible Solute ◽

Feed Forward ◽

Content Type ◽

Feed Forward Loop ◽

Ectoine Biosynthesis

ABSTRACT To maintain the turgor pressure of the cell under high osmolarity, bacteria accumulate small organic compounds called compatible solutes, either through uptake or biosynthesis. Vibrio parahaemolyticus, a marine halophile and an important human and shellfish pathogen, has to adapt to abiotic stresses such as changing salinity. Vibrio parahaemolyticus contains multiple compatible solute biosynthesis and transporter systems, including the ectABC-asp_ect operon required for de novo ectoine biosynthesis. Ectoine biosynthesis genes are present in many halotolerant bacteria; however, little is known about the mechanism of regulation. We investigated the role of the quorum sensing master regulators OpaR and AphA in ect gene regulation. In an opaR deletion mutant, transcriptional reporter assays demonstrated that ect expression was induced. In an electrophoretic mobility shift assay, we showed that purified OpaR bound to the ect regulatory region indicating direct regulation by OpaR. In an aphA deletion mutant, expression of the ect genes was repressed, and purified AphA bound upstream of the ect genes. These data indicate that AphA is a direct positive regulator. CosR, a Mar-type regulator known to repress ect expression in V. cholerae, was found to repress ect expression in V. parahaemolyticus. In addition, we identified a feed-forward loop in which OpaR is a direct activator of cosR, while AphA is an indirect activator of cosR. Regulation of the ectoine biosynthesis pathway via this feed-forward loop allows for precise control of ectoine biosynthesis genes throughout the growth cycle to maximize fitness. IMPORTANCE Accumulation of compatible solutes within the cell allows bacteria to maintain intracellular turgor pressure and prevent water efflux. De novo ectoine production is widespread among bacteria, and the ect operon encoding the biosynthetic enzymes is induced by increased salinity. Here, we demonstrate that the quorum sensing regulators AphA and OpaR integrate with the osmotic stress response pathway to control transcription of ectoine biosynthesis genes in V. parahaemolyticus. We uncovered a feed-forward loop wherein quorum sensing regulators also control transcription of cosR, which encodes a negative regulator of the ect operon. Moreover, our data suggest that this mechanism may be widespread in Vibrio species.

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Compatible-Solute-Supported Periplasmic Expression of Functional Recombinant Proteins under Stress Conditions

Applied and Environmental Microbiology ◽

10.1128/aem.66.4.1572-1579.2000 ◽

2000 ◽

Vol 66 (4) ◽

pp. 1572-1579 ◽

Cited By ~ 122

Author(s):

S. Barth ◽

M. Huhn ◽

B. Matthey ◽

A. Klimka ◽

E. A. Galinski ◽

...

Keyword(s):

Osmotic Stress ◽

Recombinant Proteins ◽

Glycine Betaine ◽

Metal Ion ◽

Halophilic Bacteria ◽

Compatible Solutes ◽

Compatible Solute ◽

Size Exclusion ◽

High Yield ◽

High Concentrations

ABSTRACT The standard method of producing recombinant proteins such as immunotoxins (rITs) in large quantities is to transform gram-negative bacteria and subsequently recover the desired protein from inclusion bodies by intensive de- and renaturing procedures. The major disadvantage of this technique is the low yield of active protein. Here we report the development of a novel strategy for the expression of functional rIT directed to the periplasmic space of Escherichia coli. rITs were recovered by freeze-thawing of pellets from shaking cultures of bacteria grown under osmotic stress (4% NaCl plus 0.5 M sorbitol) in the presence of compatible solutes. Compatible solutes, such as glycine betaine and hydroxyectoine, are low-molecular-weight osmolytes that occur naturally in halophilic bacteria and are known to protect proteins at high salt concentrations. Adding 10 mM glycine betaine for the cultivation of E. coliunder osmotic stress not only allowed the bacteria to grow under these otherwise inhibitory conditions but also produced a periplasmic microenvironment for the generation of high concentrations of correctly folded rITs. Protein purified by combinations of metal ion affinity and size exclusion chromatography was substantially stabilized in the presence of 1 M hydroxyecotine after several rounds of freeze-thawing, even at very low protein concentrations. The binding properties and cytotoxic potency of the rITs were confirmed by competitive experiments. This novel compatible-solute-guided expression and purification strategy might also be applicable for high-yield periplasmic production of recombinant proteins in different expression systems.

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The Asp20-to-Asn Substitution in the Response Regulator AdeR Leads to Enhanced Efflux Activity of AdeB in Acinetobacter baumannii

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.02413-15 ◽

2015 ◽

Vol 60 (2) ◽

pp. 1085-1090 ◽

Cited By ~ 12

Author(s):

Jennifer Nowak ◽

Thamarai Schneiders ◽

Harald Seifert ◽

Paul G. Higgins

Keyword(s):

Acinetobacter Baumannii ◽

Antimicrobial Susceptibility ◽

Efflux Pump ◽

Response Regulator ◽

Two Component System ◽

Content Type ◽

Susceptibility Data ◽

Genes Encoding ◽

Induced Changes

ABSTRACTOverexpression of the resistance-nodulation-cell division-type efflux pump AdeABC is often associated with multidrug resistance inAcinetobacter baumanniiand has been linked to mutations in the genes encoding the AdeRS two-component system. In a previous study, we reported that the Asp20→Asn amino acid substitution in the response regulator AdeR is associated withadeBoverexpression and reduced susceptibility to the antimicrobials levofloxacin, tigecycline, and trimethoprim-sulfamethoxazole. To further characterize the effect of the Asp20→Asn substitution on antimicrobial susceptibility, the expression of the efflux genesadeB,adeJ, andadeG, and substrate accumulation, four plasmid constructs [containingadeR(Asp20)S,adeR(Asn20)S,adeR(Asp20)SABC, andadeR(Asn20)SABC] were introduced into theadeRSABC-deficientA. baumanniiisolate NIPH 60. NeitheradeRSconstruct induced changes in antimicrobial susceptibility or substrate accumulation from that for the vector-only control. TheadeR(Asp20)SABCtransformant showed reduced susceptibility to 6 antimicrobials and accumulated 12% less ethidium than the control, whereas the Asn20 variant showed reduced susceptibility to 6 of 8 antimicrobial classes tested, and its ethidium accumulation was only 72% of that observed for the vector-only construct.adeBexpression was 7-fold higher in theadeR(Asn20)SABCtransformant than in its Asp20 variant. No changes inadeGoradeJexpression or in acriflavine or rhodamine 6G accumulation were detected. The antimicrobial susceptibility data suggest that AdeRS does not regulate any resistance determinants other than AdeABC. Furthermore, the characterization of the Asp20→Asn20 substitution proves that the reduced antimicrobial susceptibility previously associated with this substitution was indeed caused by enhanced efflux activity of AdeB.

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Osmotic Adaptation and Compatible Solute Biosynthesis of Phototrophic Bacteria as Revealed from Genome Analyses

Microorganisms ◽

10.3390/microorganisms9010046 ◽

2020 ◽

Vol 9 (1) ◽

pp. 46

Author(s):

Johannes F. Imhoff ◽

Tanja Rahn ◽

Sven Künzel ◽

Alexander Keller ◽

Sven C. Neulinger

Keyword(s):

Glycine Betaine ◽

Compatible Solutes ◽

Compatible Solute ◽

Phototrophic Bacteria ◽

Transport Systems ◽

Phylogenetic Groups ◽

Osmotic Adaptation ◽

Cell Structures ◽

Freshwater Bacteria ◽

Genome Analyses

Osmotic adaptation and accumulation of compatible solutes is a key process for life at high osmotic pressure and elevated salt concentrations. Most important solutes that can protect cell structures and metabolic processes at high salt concentrations are glycine betaine and ectoine. The genome analysis of more than 130 phototrophic bacteria shows that biosynthesis of glycine betaine is common among marine and halophilic phototrophic Proteobacteria and their chemotrophic relatives, as well as in representatives of Pirellulaceae and Actinobacteria, but are also found in halophilic Cyanobacteria and Chloroherpeton thalassium. This ability correlates well with the successful toleration of extreme salt concentrations. Freshwater bacteria in general lack the possibilities to synthesize and often also to take up these compounds. The biosynthesis of ectoine is found in the phylogenetic lines of phototrophic Alpha- and Gammaproteobacteria, most prominent in the Halorhodospira species and a number of Rhodobacteraceae. It is also common among Streptomycetes and Bacilli. The phylogeny of glycine-sarcosine methyltransferase (GMT) and diaminobutyrate-pyruvate aminotransferase (EctB) sequences correlate well with otherwise established phylogenetic groups. Most significantly, GMT sequences of cyanobacteria form two major phylogenetic branches and the branch of Halorhodospira species is distinct from all other Ectothiorhodospiraceae. A variety of transport systems for osmolytes are present in the studied bacteria.

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