Phospholipid composition of Desulfovibrio species

A study of bacteria adhesion and microbial corrosion on different stainless steels in environment containing Desulfovibrio vulgaris

Stainless steel is an important material used in many applications due to its mechanical strength and corrosion-resistant properties. The high corrosion resistance of stainless steel is provided by the passive film. Different stainless steels have different alloy elements and surface properties which could have a significant influence on bacterial attachment to the surface and thus might result in different microbial corrosion behaviours. In this study, the effect of adhesion of sulfate-reducing bacteria (SRB) on corrosion behaviour in artificial seawater on different stainless steels was investigated. Stainless steel materials used were SS 410, SS 420, SS 316 and DSS 2205 and pure chromium. The contact angle was measured to study the effect of surface properties of materials. Adhesion was measured by counting cells attached to the surface of materials. The corrosion behaviour of the materials was measured by electrochemical testing including measuring open circuit potential, electrochemical impedance spectroscopy and potentiodynamic behaviour. The long-term corrosion behaviour of each material was studied after six months of exposure by measuring weight loss and surface analysis with scanning electron microscope with energy-dispersive X-ray analysis. Hydrophobicity had a strong effect on bacterial attachment. Alloying elements e.g. nickel also had shown its ability to attract bacteria to adhere on the surface. However, the corrosion rate of different materials is determined not only by bacterial attachment but also by the stability of the passive film which is determined by the alloying elements, such as Mo and Cr. Chromium showed high resistance to corrosion, possibly due to toxicity on bacterial attachment. The nature of bacterial attachment and corrosion behaviour of the materials are discussed.

Sulfate-Reducing Bacteria That Produce Exopolymers Thrive in the Calcifying Zone of a Hypersaline Cyanobacterial Mat

Calcifying microbial mats in hypersaline environments are important model systems for the study of the earliest ecosystems on Earth that started to appear more than three billion years ago and have been preserved in the fossil record as laminated lithified structures known as stromatolites. It is believed that sulfate-reducing bacteria play a pivotal role in the lithification process by increasing the saturation index of calcium minerals within the mat. Strain L21-Syr-AB^T was isolated from anoxic samples of a several centimeters-thick microbialite-forming cyanobacterial mat of a hypersaline lake on the Kiritimati Atoll (Kiribati, Central Pacific). The novel isolate was assigned to the family Desulfovibrionaceae within the Deltaproteobacteria. Available 16S rRNA-based population surveys obtained from discrete layers of the mat indicate that the occurrence of a species-level clade represented by strain L21-Syr-AB^T is restricted to a specific layer of the suboxic zone, which is characterized by the presence of aragonitic spherulites. To elucidate a possible function of this sulfate-reducing bacterium in the mineral formation within the mat a comprehensive phenotypic characterization was combined with the results of a comparative genome analysis. Among the determined traits of strain L21-Syr-AB^T, several features were identified that could play a role in the precipitation of calcium carbonate: (i) the potential deacetylation of polysaccharides and consumption of substrates such as lactate and sulfate could mobilize free calcium; (ii) under conditions that favor the utilization of formate and hydrogen, the alkalinity engine within the mat is stimulated, thereby increasing the availability of carbonate; (iii) the production of extracellular polysaccharides could provide nucleation sites for calcium mineralization. In addition, our data suggest the proposal of the novel species and genus Desulfohalovibrio reitneri represented by the type strain L21-Syr-AB^T (=DSM 26903^T = JCM 18662^T).

Desulfovibrio gilichinskyi sp. nov., a cold-adapted sulfate-reducing bacterium from a Yamal Peninsula cryopeg

A psychrotolerant non-spore-forming sulfate-reducing bacterium, strain K3S^T, was isolated from a Yamal Peninsula cryopeg within permafrost. Strain K3S^T grew at subzero temperatures and required Na⁺ for growth. The new bacterium was able to use lactate, formate, pyruvate, fumarate, alanine, ethanol and molecular hydrogen as electron donors in the presence of sulfate, and used sulfate, sulfite, thiosulfate and elemental sulfur as electron acceptors in the presence of lactate. Fe(III)-citrate and Fe(III)-EDTA were reduced without visible growth. Major polar lipids were рhosphatidylserine, рhosphatidylethanolamine, phospholipids, cardiolipin and aminolipid; major cellular fatty acids were C16 : 1ω7, C16 : 0 and C18 : 1ω7; and the predominant isoprenoid quinone was MK-6 (H2). The genomic DNA G+C content was found to be 42.33 mol%. Phylogenetic analysis showed that the closest relative of the new isolate was Desulfovibrio ferrireducens strain 61^T with 97.1 % 16S rRNA gene similarity. In addition, the ANI value between strain K3S^T and D. ferrireducens 61^T was 82.1 %. On the basis of the genomic and polyphasic taxonomy data of strain K3S^T, we conclude that the strain is a representative of a novel species Desulfovibrio gilichinskyi sp. nov. (=VKM B-2877^T=DSM 100341^T).

Modeling of the Passive Permeation of Mercury and Methylmercury Complexes Through a Bacterial Cytoplasmic Membrane

Cellular uptake and export are important steps in the biotransformation of mercury (Hg) by microorganisms. However, the mechanisms of transport across biological membranes remain unclear. Membrane-bound transporters are known to be relevant, but passive permeation may also be involved. Inorganic Hg^II and methylmercury ([CH₃Hg^II]⁺) are commonly complexed with thiolate ligands. Here, we have performed extensive molecular dynamics simulations of the passive permeation of Hg^II and [CH₃Hg^II]⁺ complexes with thiolate ligands through a model bacterial cytoplasmic membrane. We find that the differences in free energy between the individual complexes in bulk water and at their most favorable position within the membrane are ∼2 kcal mol^-1. We provide a detailed description of the molecular interactions that drive the membrane crossing process. Favorable interactions with carbonyl and tail groups of phospholipids stabilize Hg-containing solutes in the tail-head interface region of the membrane. The calculated permeability coefficients for the neutral compounds CH₃S-Hg^II-SCH₃ and CH₃Hg^II-SCH₃ are on the order of 10^-5 cm s^-1. We conclude that small, nonionized Hg-containing species can permeate readily through cytoplasmic membranes.

System-Wide Adaptations of Desulfovibrio alaskensis G20 to Phosphate-Limited Conditions

The prevalence of lipids devoid of phosphorus suggests that the availability of phosphorus limits microbial growth and activity in many anoxic, stratified environments. To better understand the response of anaerobic bacteria to phosphate limitation and starvation, this study combines microscopic and lipid analyses with the measurements of fitness of pooled barcoded transposon mutants of the model sulfate reducing bacterium Desulfovibrio alaskensis G20. Phosphate-limited G20 has lower growth rates and replaces more than 90% of its membrane phospholipids by a mixture of monoglycosyl diacylglycerol (MGDG), glycuronic acid diacylglycerol (GADG) and ornithine lipids, lacks polyphosphate granules, and synthesizes other cellular inclusions. Analyses of pooled and individual mutants reveal the importance of the high-affinity phosphate transport system (the Pst system), PhoR, and glycolipid and ornithine lipid synthases during phosphate limitation. The phosphate-dependent synthesis of MGDG in G20 and the widespread occurrence of the MGDG/GADG synthase among sulfate reducing ∂-Proteobacteria implicate these microbes in the production of abundant MGDG in anaerobic environments where the concentrations of phosphate are lower than 10 μM. Numerous predicted changes in the composition of the cell envelope and systems involved in transport, maintenance of cytoplasmic redox potential, central metabolism and regulatory pathways also suggest an impact of phosphate limitation on the susceptibility of sulfate reducing bacteria to other anthropogenic or environmental stresses.

Desulfobaculum xiamenensis gen. nov., sp. nov., a member of the family Desulfovibrionaceae isolated from marine mangrove sediment

A taxonomic study was carried out on strain P1T, which was isolated from mangrove sediment samples collected from Qinglan Port (Hainan, China). Cells were curved rods, that were motile, with a single polar flagellum. The strain was non-spore-forming with a cell size of 0.6×1.5–2.2 µm. Catalase and oxidase activities were not detected. Growth was observed in the temperature range 22–44 °C (optimum, 35–40 °C) and pH range 5.5–8.5 (optimum, pH 7.0). NaCl was required for growth and tolerated at up to 3.5 % (w/v) (optimum, 0.5 %). Strain P1T utilized hydrogen, succinate, l-malate, citrate, oxalate, dl-lactate, pyruvate, or cysteine as electron donors, and sulfate or sulfite as electron acceptors. Fermentation products from pyruvate were acetate, H2 and CO2. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain P1T formed a distinct evolutionary lineage within the family Desulfovibrionaceae . Strain P1T was most closely related to members of the genera Desulfovibrio (92.0–94.3 % 16S rRNA gene sequence similarity), Desulfocurvus (91.1 %), Bilophila (87.9 %) and Lawsonia (86.0 %) of the family Desulfovibrionaceae . The DNA G+C content of strain P1T was 64.5 mol% and the major cellular fatty acids were iso-C15 : 0 (18.8 %), anteiso-C15 : 0 (5.0 %), C16 : 0 (14.2 %) and iso-C17 : 1ω9c (24.4 %). The predominant menaquinone was MK-7 (97 %). Major polar lipids were phosphatidylcholine, phosphatidylethanolamine and phosphatidylglycerol. Strain P1T was distinguishable from members of phylogenetically related genera by differences in several phenotypic properties. On the basis of the phenotypic and phylogenetic data, strain P1T represents a novel species of a new genus, for which the name Desulfobaculum xiamenensis gen. nov., sp. nov. is proposed. The type strain of Desulfobaculum xiamenensis is P1T ( = CGMCC 1.5166T = DSM 24233T).

Oxidative phosphorylation linked to the dissimilatory reduction of elemental sulphur by Desulfovibrio

Hydrogenase and cytochrome c3 purified from Desulfovibrio gigas and D. desulfuricans strain Norway form a soluble complex which is capable of transferring electrons from molecular hydrogen to colloidal sulphur (S0). In this reaction, sulphur is reduced to hydrogen sulphide. Since both strains are capable of growth using elemental sulphur as terminal electron acceptor, it was of interest to check for oxidative phosphorylation in this sulphur reduction sytem. Membranes isolated from D. gigas or D. desulfuricans strain Norway contain hydrogenase and c-type cytochromes and catalyse the H2 leads to S0 reaction. With D. gigas, esterification of orthophosphate is coupled to the membrane-mediated transfer of electrons from H2 to S0. A P/2e ratio of 0.1 was observed and this value could be reduced by the addition of colloidal sulphur with c2 may be more than a purely chemical reaction. Since whole cells can use sulphur flower while cell-free extracts react only with colloidal sulphur, it is evident that cells handle sulphur in a way which is not yet fully understood.

Hydrogenases in Desulfovibrio vulgaris Hildenborough: structural and physiologic characterisation of the membrane-bound [NiFeSe] hydrogenase

The genome of Desulfovibrio vulgaris Hildenborough (DvH) encodes for six hydrogenases (Hases), making it an interesting organism to study the role of these proteins in sulphate respiration. In this work we address the role of the [NiFeSe] Hase, found to be the major Hase associated with the cytoplasmic membrane. The purified enzyme displays interesting catalytic properties, such as a very high H(2) production activity, which is dependent on the presence of phospholipids or detergent, and resistance to oxygen inactivation since it is isolated aerobically in a Ni(II) oxidation state. Evidence was obtained that the [NiFeSe] Hase is post-translationally modified to include a hydrophobic group bound to the N-terminal, which is responsible for its membrane association. Cleavage of this group originates a soluble, less active form of the enzyme. Sequence analysis shows that [NiFeSe] Hases from Desulfovibrionacae form a separate family from the [NiFe] enzymes of these organisms, and are more closely related to [NiFe] Hases from more distant bacterial species that have a medial [4Fe4S](2+/1+) cluster, but not a selenocysteine. The interaction of the [NiFeSe] Hase with periplasmic cytochromes was investigated and is similar to the [NiFe](1) Hase, with the Type I cytochrome c (3) as the preferred electron acceptor. A model of the DvH [NiFeSe] Hase was generated based on the structure of the Desulfomicrobium baculatum enzyme. The structures of the two [NiFeSe] Hases are compared with the structures of [NiFe] Hases, to evaluate the consensual structural differences between the two families. Several conserved residues close to the redox centres were identified, which may be relevant to the higher activity displayed by [NiFeSe] Hases.

Intraspecies variability of cellular fatty acids among soil and intestinal strains of Desulfovibrio desulfuricans

A comparison of cellular fatty acid profiles of Desulfovibrio desulfuricans DSM 642 and 14 wild strains of this species, isolated from two completely different environments, soil and the human intestine, was carried out. All the D. desulfuricans strains grown on lactate and sulfate indicated the presence of considerable amounts of i-C15:0, i-C17:1 and C16:0. Although differences in the quantities of individual fatty acids present in each strain were clear in the group of soil strains (similarity, 67.6%), in contrast to almost identical fatty acid patterns (similarity, near 100%) in the intestinal strains, the results were variable within the limits acceptable for species demonstration. The higher similarity of the fatty acid profiles of intestinal strains may be a result of the similarity of biocenoses in the human digestive tract. The coefficients of variability of i-C17:1 and i-C15:0 (the major branched-chain fatty acids), as well as clustering of the investigated strains compared with strains described in the literature after plotting percentages of i-C17:1 fatty acid against i-C15:0 fatty acid, confirmed a certain heterogeneity of cellular fatty acid profiles within the group of soil strains, in contrast to almost ideal homogeneity within the group of intestinal isolates. Intestinal strains contained a higher ratio of saturated to unsaturated fatty acids (2.2 +/- 0.14) than did soil strains (1.6 +/- 0.2; in one case, 2.7). We propose that intestinal D. desulfovibrio bacteria should be assumed to be a highly homogeneous group and should be represented by the strain D. desulfuricans subsp. intestinus in collections of microbial cultures.

Lipid metabolism in anaerobic ecosystems

In anaerobic ecosystems, acyl lipids are initially hydrolyzed by microbial lipases with the release of free fatty acids. Glycerol, galactose, choline, and other non-fatty acid components released during hydrolysis are fermented to volatile fatty acids by the fermentative bacteria. Fatty acids are not degraded further in the rumen or other parts of the digestive tract but are subjected to extensive biohydrogenation especially in the rumen. However, in environments such as sediments and waste digestors, which have long retention times, both long and short chain fatty acids are beta-oxidized to acetate by a special group of bacteria, the H2-producing syntrophs. Long chain fatty acids can also be degraded by alpha-oxidation. Biotransformation of bile acids, cholesterol, and steroids by intestinal microorganisms is extensive. Many rumen bacteria have specific growth requirements for fatty acids such as n-valeric, iso-valeric, 2-methylbutyric, and iso-butyric acids. Some species have requirements for C13 to C18 straight-chain saturated or monoenoic fatty acids for growth.

Brucella abortus 16S rRNA and lipid A reveal a phylogenetic relationship with members of the alpha-2 subdivision of the class Proteobacteria

On the basis of ribosomal 16S sequence comparison, Brucella abortus has been found to be a member of the alpha-2 subdivision of the class Proteobacteria (formerly named purple photosynthetic bacteria and their nonphototrophic relatives). Within the alpha-2 subgroup, brucellae are specifically related to rickettsiae, agrobacteria, and rhizobiae, organisms that also have the faculty or the obligation of living in close association to eucaryotic cells. The composition of Brucella lipid A suggests a close phylogenetical relationship with members of the alpha-2 group. The chemical analysis of the lipid A fraction revealed that Brucella species contain both glucosamine and diaminoglucose, thus suggesting the presence of a so-called mixed lipid A type. The serological analysis with polyclonal and monoclonal antibodies is in agreement with the existence of mixed lipid A type in B. abortus. The amide-linked fatty acid present as acyl-oxyacyl residues were 3-O-C(16:0)12:0, 3-O-C(16:0)13:0, 3-O-C(16:0)14:0, and 3-O-C(18:0)14:0. The only amide-linked unsubstituted fatty acid detected was 3-OH-C16:0. The ester-linked fatty acids are 3-OH-C16:0, 3-OH-C18:0, C16:0, C17:0, and C18:0. Significant amounts of the large-chain 27-OH-C28:0 were detected together with traces of 25-OH-C26:0 and 29-OH-C30:0. Comparison of the Brucella lipid composition with that of the other Proteobacteria also suggests a close phylogenetical relationship with members of the alpha-2 subdivision. The genealogical grouping of Brucella species with pericellular and intracellular plant and animal pathogens as well as with intracellular plant symbionts suggests a possible evolution of Brucella species from plant-arthropod-associated bacteria.

Phospholipid biosynthesis in some anaerobic bacteria

We have identified and characterized enzymes of phospholipid synthesis in two plasmalogen-rich anaerobes. Megasphaera elsdenii and Veillonella parvula, and one anaerobe lacking plasmalogens. Desulfovibrio vulgaris. All three species contained phosphatidate cytidylyltransferase and phosphatidylserine synthase. Phosphatidylglycerophosphate synthesis was detected only D. vulgaris extracts. Phosphatidylserine (diacyl form) was the major product of the phosphatidylserine synthase assay with particles from M. elsdenii or V. parvula. The amounts of phosphatidylethanolamine formed were very low. Only D. vulgaris particles had an active phosphatidylserine decarboxylase.

Phospholipid composition of gliding bacteria: oral isolates of Capnocytophaga compared with Sporocytophaga

The distribution of acetone-soluble (neutral glycolipid) and acetone-insoluble (phospholipid isoprenoids) lipids in oral isolates of gram-negative gliding bacteria of the genus Capnocytophaga was compared with those in a non-host-related gliding bacterium, Sporocytophaga myxococcoides. The acetone-soluble material accounted for 34 to 55% of the extracted lipids; the remainder was acetone-insoluble material. The major phospholipid was phosphatidylethanolamine (67%), with lesser amounts of lysophosphatidylethanolamine and several unidentified phosphate-containing compounds. Capnocytophaga also contained significant amounts of an ornithine-amino lipid.

Phospholipid composition of methane-utilizing bacteria

The phospholipids of Methylococcus capsulatus, Methylosinus trichosporium, La Paz, and OBT were examined in relation to their qualitative and quantitative composition. M. capsulatus exhibited a phospholipid composition consisting of phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, and phosphatidyl-choline. The esterified fatty acids were predominantly C16:0 and C16:1. M. trichosporium, La Paz, and OBT exhibited an essentially identical phospholipid composition consisting of phosphatidylmonomethylethanolamine, phosphatidyl-dimethylethanolamine, phosphatidylcholine, and phosphatidylglycerol. Only trace amounts (less than 1%) of cardiolipin were found in these organisms. The major esterified fatty acid in these organisms was C18:1 (87 to 90%). The monounsaturated fatty acids from all four organisms consisted of both cis and trans isomers, each of which contained delta8, delta9, delta10, and delta11 double-bond positional isomers.

Identification and synthesis of acyl-phosphatidylglycerol in Acinetobacter sp. HO1-N

A minor phospholipid from Acinetobacter sp. HO1-N was identified as acyl-phosphatidylglycerol. Acyl-phosphatidylglycerol synthesis by outer-membrane preparations appeared to be a result of phospholipase A activity.

Characterization of lysocardiolipin from Acinetobacter sp. HO1-N

Triacyl-lysocardiolipin (triacyl-LCL) and diacyl-LCL were isolated from Acinetobacter sp. HO1-N, and their structures were determined by chemical, physical, and enzymatic procedures. Deacylation of triacyl-LCL and diacyl-LCL yielded bis-glycerylphosphorylglycerol. Periodate oxidation of both lysolipids was negative. Diglyceride and 2-monoglyceride resulted from the acetic acid hydrolysis of triacyl-LCL, whereas 2-monoglyceride was the sole product obtained from diacyl-LCL. Cardiolipin (CL)-specific phospholipase D treatment of triacyl-LCL yielded lysophosphatidylglycerol and phosphatidic acid. Pancreatic lipase treatment of CL yielded triacyl-LCL and diacyl-LCL. 31P nuclear magnetic resonance spectrometry showed two resonance peaks separated by 40 HZ for CL, two overlapping peaks separated by 14 HZ for triacyl-LCL, and one peak for diacyl-LCL. The proportion of lysocardiolipin increased as a function of cell age, representing 2 to 3% of the total phospholipids in early- and mid-exponential growth, 5 to 7% in late-exponential growth, and 12% in the stationary growth phase.

Significance and taxonomic value of iso and anteiso monoenoic fatty acids and branded beta-hydroxy acids in Desulfovibrio desulfuricans

The fatty acids obtained from extractable lipids of the anaerobic sulfate bacterium Desulfovibrio desulfuricans were identified. Saturated and monoenoic iso (C15-C19) and anteiso (C15, C17) fatty acids and saturated normal (C14-C18) and monoenoic normal (C16, C18) fatty acids were shown to be shown to be present by capillary gas chromatography-mass spectrometry. Iso and anteiso beta-hydroxy fatty acids were analyzed as trimethylsilyl ethers in the same way. The position of methyl branches in the monoenoic fatty acids was determined from characteristic fragment ions in the mass spectra of their methyl esters. Disilyloxy methyl esters, prepared by derivatization of the mono unsaturated methyl esters and analyzed by capillary gas chromatography-mass spectrometry, provided the position of double bonds. The monoenoic fatty acids identified in this way were normal (delta7-C16:1, delta9-C16:1, delta9-C18:1, delta11-C18:1), iso (delta7-C15:1, delta9-C16:1, delta9-C17:1, delta11-C18:1, delta11-C19:1), and anteiso (delta7-C15:1, delta9-C17:1). Iso delta9-C17:1 fatty acid is present as the major component. The occurrence of these monoenoic fatty acids in this bacterium is of taxonomical importance.

Phospholipid composition and phospholipase A activity of Neisseria gonorrhoeae

Exponential-phase cells of Neisseria gonorrhaeae 2686 were examined for phospholipid composition and for membrane-associated phospholipase A activity. When cells were harvested by centrifugation, washed, and lyophilized before extraction, approximately 74% of the total phospholipid was phosphatidylethanolamine, 18% was phosphatidylglycerol, 2% was cardiolipin, and 10% was lysophosphatidylethanolamine. However, when cells still suspended in growth medium were extracted, the amount of lysophosphatidylethanolamine decreased to approximately 1% of the phospholipid composition. This suggests that a gonococcal phospholipase A may be activated by conditions encountered during centrifugation and/or lyophilization of cells preceding extraction. Phospholipase A activity associated with cell membranes was assayed by measuring the conversion of tritiated phosphatidylethanolamine to lysophosphatidylethanolamine. Optimal activity was demonstrated in 10% methanol at pH 8.0 to 8.5, in the presence of calcium ions. The activity was both detergent sensitive and thermolabile. Comparisons of gonococcal colony types 1 and 4 showed no significant differences between the two types with respect to either phospholipid content or phospholipase A activity.

Isolation and characterization of an ornithine-containing lipid from Desulfovibrio gigas

The isolation and characterization of an ornithine-containing lipid obtained from Desulfovibrio gigas are reported. The general structure for this aminolipid is represented by NH2-CH2-(CH)2-CHNH(CO-CH2CH(O-COR2)-R1)-COOH, where R1 represents 3-hydroxy palmitate linked through an amide bond to the alpha-amino group of ornithine, and R2 represents a complex variety of fatty acids esterified to the hydroxyl group of 3-hydroxy palmitate. Fatty acids characterized were n-C14:0 (21%), iso-C14:0 (14%) anteiso-C15:0 (43%), n-C16:0 (2%), n-C18:0 (8%), and n-C 18:1 (11%). The quantitative relationships between aminolipid and phospholipids showed the aminolipid to represent the major polar lipid. Isolation of the cytoplasmic and outer membranes of D. gigas showed the aminolipid to be evenly distributed between both membrane fractions, suggesting a compensatory role in phospholipid-deficient membranes.