Simultaneous sulfate reduction and copper removal by a PVA-immobilized sulfate reducing bacterial culture.

The effect of a sulfate reducing bacteria immobilized in polyvinyl alcohol (PVA) on simultaneous sulfate reduction and copper removal was investigated. Batch experiments were designed using central composite design (CCD) with two parameters, i.e. the copper concentration (10-100mg/L), and the quantity of immobilized SRB in culture solution (19-235 mg of VSS/L). Response surface methodology (RSM) was used to model the experimental data, and to identify optimal conditions for the maximum sulfate reduction and copper removal. Under optimum condition, i.e. approximately 138.5mg VSS/L of sulfate reducing bacteria immobilized in PVA, and approximately 51.5mg/L of copper, the maximum sulfate reduction rate was 1.57 d(-1) as based on the first-order kinetic equation. The data demonstrate that immobilizing sulfate reducing bacteria in PVA can enhance copper removal and the resistance of the bacteria towards copper toxicity.

Isolation and characterization of a mesophilic heavy-metals-tolerant sulfate-reducing bacterium Desulfomicrobium sp. from an enrichment culture using phosphogypsum as a sulfate source.

A sulfate-reducing bacterium, was isolated from a 6 month trained enrichment culture in an anaerobic media containing phosphogypsum as a sulfate source, and, designated strain SA2. Cells of strain SA2 were rod-shaped, did not form spores and stained Gram-negative. Phylogenetic analysis of the 16S rRNA gene sequence of the isolate revealed that it was related to members of the genus Desulfomicrobium (average sequence similarity of 98%) with Desulfomicrobium baculatum being the most closely related (sequence similarity of 99%). Strain SA2 used thiosulfate, sulfate, sulfite and elemental sulfur as electron acceptors and produced sulfide. Strain SA2 reduced sulfate contained in 1-20g/L phosphogypsum to sulfide with reduction of sulfate contained in 2g/L phosphogypsum being the optimum concentration. Strain SA2 grew with metalloid, halogenated and non-metal ions present in phosphogypsum and with added high concentrations of heavy metals (125ppm Zn and 100ppm Ni, W, Li and Al). The relative order for the inhibitory metal concentrations, based on the IC(50) values, was Cu, Te>Cd>Fe, Co, Mn>F, Se>Ni, Al, Li>Zn.

Sulfite-oxido-reductase is involved in the oxidation of sulfite in Desulfocapsa sulfoexigens during disproportionation of thiosulfate and elemental sulfur.

The enzymatic pathways of elemental sulfur and thiosulfate disproportionation were investigated using cell-free extract of Desulfocapsa sulfoexigens. Sulfite was observed to be an intermediate in the metabolism of both compounds. Two distinct pathways for the oxidation of sulfite have been identified. One pathway involves APS reductase and ATP sulfurylase and can be described as the reversion of the initial steps of the dissimilatory sulfate reduction pathway. The second pathway is the direct oxidation of sulfite to sulfate by sulfite oxidoreductase. This enzyme has not been reported from sulfate reducers before. Thiosulfate reductase, which cleaves thiosulfate into sulfite and sulfide, was only present in cell-free extract from thiosulfate disproportionating cultures. We propose that this enzyme catalyzes the first step in thiosulfate disproportionation. The initial step in sulfur disproportionation was not identified. Dissimilatory sulfite reductase was present in sulfur and thiosulfate disproportionating cultures. The metabolic function of this enzyme in relation to elemental sulfur or thiosulfate disproportionation was not identified. The presence of the uncouplers HQNO and CCCP in growing cultures had negative effects on both thiosulfate and sulfur disproportionation. CCCP totally inhibited sulfur disproportionation and reduced thiosulfate disproportionation by 80% compared to an unamended control. HQNO reduced thiosulfate disproportionation by 80% and sulfur disproportionation by 90%.

Big bacteria.

A small number of prokaryotic species have a unique physiology or ecology related to their development of unusually large size. The biomass of bacteria varies over more than 10 orders of magnitude, from the 0.2 microm wide nanobacteria to the largest cells of the colorless sulfur bacteria, Thiomargarita namibiensis, with a diameter of 750 microm. All bacteria, including those that swim around in the environment, obtain their food molecules by molecular diffusion. Only the fastest and largest swimmers known, Thiovulum majus, are able to significantly increase their food supply by motility and by actively creating an advective flow through the entire population. Diffusion limitation generally restricts the maximal size of prokaryotic cells and provides a selective advantage for microm-sized cells at the normally low substrate concentrations in the environment. The largest heterotrophic bacteria, the 80 x 600 microm large Epulopiscium sp. from the gut of tropical fish, are presumably living in a very nutrient-rich medium. Many large bacteria contain numerous inclusions in the cells that reduce the volume of active cytoplasm. The most striking examples of competitive advantage from large cell size are found among the colorless sulfur bacteria that oxidize hydrogen sulfide to sulfate with oxygen or nitrate. The several-cm-long filamentous species can penetrate up through the ca 500-microm-thick diffusive boundary layer and may thereby reach into water containing their electron acceptor, oxygen or nitrate. By their ability to store vast quantities of both nitrate and elemental sulfur in the cells, these bacteria have become independent of the coexistence of their substrates. In fact, a close relative, T. namibiensis, can probably respire in the sulfidic mud for several months before again filling up their large vacuoles with nitrate.

[Characteristics of morphology and ultrastructure of bacteria of the genus Dethiosulfovibrio]. / Osobennosti morfologii i ul'trastruktury bakterii roda Dethiosulfovibrio.

Cell morphology and fine structure were studied in two strains of rod-shaped, strictly anaerobic, gram-negative sulfidogenic bacteria: strain SR12T (DSM 12538) and strain WS100 (DSM 12537) belonging to "Dethiosulfovibrio starorussensis." Cells of both strains, as well as cells of the type species of the genus Dethiosulfovibrio, D. peptidovorans, were found to possess multiple intracellular incomplete cross septa in the stationary growth phase.

Desulfotomaculum alkaliphilum sp. nov., a new alkaliphilic, moderately thermophilic, sulfate-reducing bacterium.

A new moderately thermophilic, alkaliphilic, sulfate-reducing, chemolithoheterotrophic bacterium, strain S1T, was isolated from a mixed cow/pig manure with neutral pH. The bacterium is an obligately anaerobic, non-motile, Gram-positive, spore-forming curved rod growing within a pH range of 8.0-9.15 (optimal growth at pH 8.6-8.7) and temperature range of 30-58 degrees C (optimal growth at 50-55 degrees C). The optimum NaCl concentration for growth is 0.1%. Strain S1T is an obligately carbonate-dependent alkaliphile. The G+C content of the DNA is 40.9 mol%. A limited number of compounds are utilized as electron donors, including H2+acetate, formate, ethanol, lactate and pyruvate. Sulfate, sulfite and thiosulfate, but not sulfur or nitrate, can be used as electron acceptors. Strain S1T is able to utilize acetate or yeast extract as sources of carbon. Analysis of the 16S rDNA sequence allowed strain S1T (= DSM 12257T) to be classified as a representative of a new species of the genus Desulfotomaculum, Desulfotomaculum alkaliphilum sp. nov.

Desulfovirga adipica gen. nov., sp. nov., an adipate-degrading, gram-negative, sulfate-reducing bacterium.

A novel, mesophilic, Gram-negative bacterium was isolated from an anaerobic digestor for municipal wastewater. The bacterium degraded adipate in the presence of sulfate, sulfite, thiosulfate and elemental sulfur. (E)-2-Hexenedioate accumulated transiently in the degradation of adipate. (E)-2-Hexenedioate, (E)-3-hexenedioate, pyruvate, lactate, C1-C12 straight-chain fatty acids and C2-C10 straight-chain primary alcohols were also utilized as electron donors. 3-Phenylpropionate was oxidized to benzoate. The G + C content of the DNA was 60 mol%. 16S rDNA sequence analysis revealed that the new isolate clustered with species of the genus Syntrophobacter and Desulforhabdus amnigenus. Strain TsuAS1T resembles Desulforhabdus amnigenus DSM 10338T with respect to the ability to utilize acetate as an electron donor and the inability to utilize propionate without sulfate in co-culture with Methanospirillum hungatei DSM 864. Strains TsuAS1T and DSM 10338T form a 'non-syntrophic subcluster' within the genus Syntrophobacter. Desulfovirga adipica gen. nov., sp. nov. is proposed for the newly isolated bacterium, with strain TsuAS1T (= DSM 12016T) as the type strain.

Psychrophilic sulfate-reducing bacteria isolated from permanently cold arctic marine sediments: description of Desulfofrigus oceanense gen. nov., sp. nov., Desulfofrigus fragile sp. nov., Desulfofaba gelida gen. nov., sp. nov., Desulfotalea psychrophila gen. nov., sp. nov. and Desulfotalea arctica sp. nov.

Five psychrophilic, Gram-negative, sulfate-reducing bacteria were isolated from marine sediments off the coast of Svalbard. All isolates grew at the in situ temperature of -1.7 degrees C. In batch cultures, strain PSv29T had the highest growth rate at 7 degrees C, strains ASv26T and LSv54T had the highest growth rate at 10 degrees C, and strains LSv21T and LSv514T had the highest growth rate at 18 degrees C. The new isolates used the most common fermentation products in marine sediments, such as acetate, propionate, butyrate, lactate and hydrogen, but only strain ASv26T was able to oxidize fatty acids completely to CO2. The new strains had growth optima at neutral pH and marine salt concentration, except for LSv54T which grew fastest with 1% NaCl. Sulfite and thiosulfate were used as electron acceptors by strains ASv26T, PSv29T and LSv54T, and all strains except PSv29T grew with Fe3+ (ferric citrate) as electron acceptor. Chemotaxonomy based on cellular fatty acid patterns and menaquinones showed good agreement with the phylogeny based on 16S rRNA sequences. All strains belonged to the delta subclass of Proteobacteria but had at least 9% evolutionary distance from known sulfate reducers. Due to the phylogenetic and phenotypic differences between the new isolates and their closest relatives, establishment of the new genera Desulfotalea gen. nov., Desulfofaba gen. nov. and Desulfofrigus gen. nov. is proposed, with strain ASv26T as the type strain of the type species Desulfofrigus oceanense sp. nov., LSv21T as the type strain of Desulfofrigus fragile sp. nov., PSv29T as the type strain of the type species Desulfofaba gelida sp. nov., LSv54T as the type strain of the type species Desulfotalea psychrophila sp. nov. and LSv514T as the type strain of Desulfotalea arctica sp. nov.

Phylogenetic relationships of filamentous sulfur bacteria (Thiothrix spp. and Eikelboom type 021N bacteria) isolated from wastewater-treatment plants and description of Thiothrix eikelboomii sp. nov., Thiothrix unzii sp. nov., Thiothrix fructosivorans sp. nov. and Thiothrix defluvii sp. nov.

The relationship of mixotrophic and autotrophic Thiothrix species to morphologically similar chemoorganotrophic bacteria (e.g. Leucothrix species, Eikelboom type 021N bacteria) has been a matter of debate for some years. These bacteria have alternatively been grouped together on the basis of shared morphological features or separated on the basis of their nutrition. Many of these bacteria are difficult to maintain in axenic culture and, until recently, few isolates were available to allow comprehensive phenotypic and genotypic characterization. Several isolates of Thiothrix spp. and Eikelboom type 021N strains were characterized by comparative 16S rRNA sequence analysis. This revealed that the Thiothrix spp. and Eikelboom type 021N isolates formed a monophyletic group. Furthermore, isolates of Eikelboom type 021N bacteria isolated independently from different continents were phylogenetically closely related. The 16S rRNA sequence-based phylogeny was congruent with the morphological similarities between Thiothrix and Eikelboom type 021N. However, one isolate examined in this study (Ben47) shared many morphological features with the Thiothrix spp. and Eikelboom type 021N isolates, but was not closely related to them phylogenetically. Consequently, morphology alone cannot be used to assign bacteria to the Thiothrix/type 021N group. Comparative 16S rRNA sequence analysis supports monophyly of the Thiothrix/type 021N group, and phenotypic differences between the Thiothrix spp. and Eikelboom type 021N bacteria are currently poorly defined. For example, both groups include heterotrophic organisms that deposit intracellular elemental sulfur. It is therefore proposed that the Eikelboom type 021N bacteria should be accommodated within the genus Thiothrix as a new species, Thiothrix eikelboomii sp. nov., and three further new Thiothrix species are described: Thiothrix unzii sp. nov., Thiothrix fructosivorans sp. nov. and Thiothrix defluvii sp. nov.

Hippea maritima gen. nov., sp. nov., a new genus of thermophilic, sulfur-reducing bacterium from submarine hot vents.

Three strains of moderately thermophilic, sulfur-reducing bacteria were isolated from shallow-water hot vents of the Bay of Plenty (New Zealand) and Matupi Harbour (Papua New Guinea). Cells of all isolates were short, Gram-negative, motile rods with one polar flagellum. All strains were obligate anaerobes and grew optimally at pH 5.8-6.2, 52-54 degrees C and 2.5-3% (w/v) NaCl. Growth substrates were molecular hydrogen, acetate and saturated fatty acids; one of the strains, isolated from Matupi Harbour, was able to utilize ethanol. Elemental sulfur was required for growth. H2S and CO2 were the only growth products. No growth occurred in the absence of 100 mg yeast extract I-1. The G+C content of the DNA determined for the type strain MH2T was 40.4 mol%. Results of 16S rDNA sequencing indicated that these strains represent a distinct lineage most closely related to the genus Desulfurella. On the basis of the results of morphological, physiological and phylogenetic studies, a new genus, Hippea gen. nov., is proposed with the type species Hippea maritima gen. nov., sp. nov., of which the type strain is MH2T (= DSM 10411T).

Metabolism of explosive compounds by sulfate-reducing bacteria.

The metabolism of various explosive compounds-1,3,5-trinitrobenzene (TNB), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX)-by a sulfate-reducing bacterial consortium, Desulfovibrio spp., was studied. The results indicated that the Desulfovibrio spp. used all of the explosive compounds studied as their sole source of nitrogen for growth. The concentrations of TNB, RDX, and HMX in the culture media dropped to below the detection limit (<0.5 ppm) within 18 days of incubation. We also observed the production of ammonia from the nitro groups of the explosive compounds in the culture media. This ammonia served as a nitrogen source for the bacterial growth, and the concentration of ammonia later dropped to <0.5 mg/L. The sulfate-reducing bacteria may be useful in the anaerobic treatment of explosives-contaminated soil.