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.

Complementary effects of nanosilver and superhydrophobic coatings on the prevention of marine bacterial adhesion.

A superhydrophobic coating composed of silver nanoparticles enclosed in multilayered polyelectrolyte films was deposited onto copper with the aim of preventing bacterial adhesion. Observations from scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the amplified exponential growth of the multilayers could induce distinguishable, hierarchical micro- and nanostructures simultaneously. This growth caused the surface roughness to amplify in a lotus-leaf-like manner. UV/visible spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) confirmed the formation of well-dispersed Ag(0) nanoparticles (with sizes from 4-6 nm) in the films. SEM and fluorescence microscope images of the exposed surfaces revealed that the pattern of adhesion and the density of bacterial cells differed depending on the surface energy and the number of Ag(+) ions released during the various immersion time periods. The complementary effects of nanosilver and superhydrophobic coatings can help to effectively reduce bacterial adhesion and the formation of biofilms.

Desulfovibrio tunisiensis sp. nov., a novel weakly halotolerant, sulfate-reducing bacterium isolated from exhaust water of a Tunisian oil refinery.

A novel weakly halotolerant, sulfate-reducing bacterium, designated strain RB22(T), was isolated from exhaust water of a Tunisian oil refinery. Cells of strain RB22(T) were Gram-negative, motile, vibrio-shaped or sigmoid and non-spore-forming, and occurred singly or in chains. Strain RB22(T) grew between 15 and 45 degrees C (optimum, 37 degrees C) and at pH 4.5 to 9 (optimum, pH 7). NaCl was not required for growth, but the strain tolerated high NaCl concentrations (up to 70 g l(-1)) with an optimum of 40 g l(-1). Sulfate, thiosulfate, sulfite and elemental sulfur served as electron acceptors, but not fumarate. Nitrate and nitrite were not reduced. Strain RB22(T) utilized lactate, formate, fumarate, succinate, glycerol, H(2)+CO(2) and methanol as substrates. The DNA G+C content was found to be 59.6 mol%. Phylogenetic analysis based on the 16S rRNA gene revealed that the isolate was a member of the genus Desulfovibrio, with no close relatives at the species level (16S rRNA gene sequence similarity of less than 95 %). Strain RB22(T) exhibited levels of 16S rRNA gene sequence similarity of 94.6 and 94.12 % to the type strains of the closely related species Desulfovibrio aespoeensis and Desulfovibrio dechloracetivorans, respectively. On the basis of genotypic and phylogenetic characteristics, and significant phenotypic differences, we suggest that strain RB22(T) represents a novel species, for which the name Desulfovibrio tunisiensis sp. nov. is proposed. The type strain is RB22(T) (=NCIMB 14400(T)=JCM 15076(T)=DSM 19275(T)).

Desulfovibrio alaskensis sp. nov., a sulphate-reducing bacterium from a soured oil reservoir.

A novel sulphate-reducing bacterium (Al1T) was recovered from a soured oil well in Purdu Bay, Alaska. Light and atomic force microscopy observations revealed that cells were Gram-negative, vibrio-shaped and motile by means of a single polar flagellum. The carbon and energy sources used by the isolate and the salinity, temperature and pH ranges facilitating its growth proved to be typical of a partial lactate-oxidizing, moderately halophilic, mesophilic, sulphate-reducing bacterium. Analysis of the fatty acid profile revealed that C(18 : 0), isoC(15 : 0) and isoC(17 : 1)omega7c were the predominant species. Fatty acid profile and complete 16S rRNA gene sequencing demonstrated the similarity between strain Al1T and members of the genus Desulfovibrio. The position of strain Al1T within the phylogenetic tree indicated that it clustered closely with Desulfovibrio vietnamensis DSM 10520T (98.9 % sequence similarity), a strain recovered from a similar habitat. However, whole-cell protein profiles, Fourier-transform infrared studies and DNA-DNA hybridization demonstrated that, in spite of the high level of 16S rRNA gene sequence similarity, there is sufficient dissimilarity at the DNA sequence level between D. vietnamensis DSM 10520T and strain Al1T (10.2 % similarity) to propose that strain Al1T belongs to a separate species within the genus Desulfovibrio. Based on the results obtained, the name Desulfovibrio alaskensis sp. nov. is therefore proposed, with Al1T (= NCIMB 13491T = DSM 16109T) as the type strain.

Uranium complexes formed at hematite surfaces colonized by sulfate-reducing bacteria.

Modeling uranium (U) transport in subsurface environments requires a thorough knowledge of mechanisms likely to restrict its mobility, such as surface complexation, precipitation, and colloid formation. In closed systems, sulfate-reducing bacteria (SRB) such as Desulfovibrio spp. demonstrably affect U immobilization by enzymatic reduction of U(VI) species (primarily the uranyl ion, UO2(2+), and its complexes) to U(IV). However, our understanding of such interactions under chronic U(VI) exposure in dynamic systems is limited. As a first step to understanding such interactions, we performed bioreactor experiments under continuous flow to study the effect of a biofilm of the sulfate-reducing bacterium Desulfovibrio desulfuricans attached to specular hematite (alpha-Fe2O3) surfaces on surface-associated U(VI) complexation, transformation, and mobility. Employing real-time microscopic observation and X-ray photoelectron spectroscopy (XPS), we show that the characteristics of the U(VI) complex(es) formed at the hematite surface are influenced by the composition of the bulk aqueous phase flowing across the surface and bythe presence of surface-associated SRB. The XPS data further suggest higher levels of U associated with hematite surfaces colonized by SRB than with bacteria-free surfaces. Microscopic observations indicate that at least a portion of the U(VI) that accumulates in the presence of the SRB is exterior to the cells, possibly associated with the extracellular biofilm matrix. The U4f7/2 core-region spectrum and U5f2 valence-band spectrum provide preliminary evidence that the SRB-colonized hematite surface accumulates both U(VI) and U(IV) phases, whereas only the U(VI) phase(s) accumulates on uncolonized hematite surfaces. The results suggest that mineral surfaces exposed to a continuously replenished supply of U(VI)-containing aqueous phase will accumulate U phases that may be more representative of those that exist in U-contaminated aquifers than those which accumulate in closed experimental systems. These phases should be considered in models attempting to predict U transport through subsurface environments.

Desulfovibrio longus sp. nov., a sulfate-reducing bacterium isolated from an oil-producing well.

A novel type of sulfate-reducing bacteria with unusual morphology was isolated from an oil-producing well in the Paris Basin. The cells of this bacterium, strain SEBR 2582T (T = type strain), are long, thin, flexible rods, contain desulfoviridin, and are physiologically similar to members of the genus Desulfovibrio. On the basis of 16S rRNA sequence data, this strain should be included in the genus Desulfovibrio. However, strain SEBR 2582T differs from other members of this genus morphologically, physiologically, and phylogenetically. Thus, a new species, Desulfovibrio longus sp. nov., is proposed for this organism.