Anaerobic Sulfide Oxidation with Nitrate by a Freshwater Beggiatoa Enrichment Culture

A lithotrophic freshwater Beggiatoa strain was enriched in O₂-H₂S gradient tubes to investigate its ability to oxidize sulfide with NO₃⁻ as an alternative electron acceptor. The gradient tubes contained different NO₃⁻ concentrations, and the chemotactic response of the Beggiatoa mats was observed. The effects of the Beggiatoa sp. on vertical gradients of O₂, H₂S, pH, and NO₃⁻ were determined with microsensors. The more NO₃⁻ that was added to the agar, the deeper the Beggiatoa filaments glided into anoxic agar layers, suggesting that the Beggiatoa sp. used NO₃⁻ to oxidize sulfide at depths below the depth that O₂ penetrated. In the presence of NO₃⁻ Beggiatoa formed thick mats (>8 mm), compared to the thin mats (ca. 0.4 mm) that were formed when no NO₃⁻ was added. These thick mats spatially separated O₂ and sulfide but not NO₃⁻ and sulfide, and therefore NO₃⁻ must have served as the electron acceptor for sulfide oxidation. This interpretation is consistent with a fourfold-lower O₂ flux and a twofold-higher sulfide flux into the NO₃⁻-exposed mats compared to the fluxes for controls without NO₃⁻. Additionally, a pronounced pH maximum was observed within the Beggiatoa mat; such a pH maximum is known to occur when sulfide is oxidized to S⁰ with NO₃⁻ as the electron acceptor.     

Phylogeny and distribution of nitrate-storing Beggiatoa spp. in coastal marine sediments

Filamentous sulphide-oxidizing Beggiatoa spp. often occur in large numbers in the coastal seabed without forming visible mats on the sediment surface. We studied the diversity, population structure and the nitrate-storing capability of such bacteria in the Danish Limfjorden and the German Wadden Sea. Their distribution was compared to the vertical gradients of O2, NO3- and H2S as measured by microsensors. The main Beggiatoa spp. populations occurred in a 0.5-3 cm thick intermediate zone, below the depth of oxygen and nitrate penetration but above the zone of free sulphide. The Beggiatoa spp. filaments were found to store nitrate, presumably in liquid vacuoles up to a concentration of 370 mM NO3-, similar to the related large marine sulphur bacteria, Thioploca and Thiomargarita. The observations indicate that marine Beggiatoa spp. can live anaerobically and conserve energy by coupling sulphide oxidation with the reduction of nitrate to dinitrogen and/or ammonia. Calculations of the diffusive nitrate flux and the potential sulphide oxidation by Beggiatoa spp. show that the bacteria may play a critical role for the sulphur cycling and the nitrogen balance in these coastal environments. 16S rDNA sequence analysis shows a large diversity of these uncultured, nitrate-storing Beggiatoa spp. Smaller (9-17 micro m wide) and larger (33-40 micro m wide) Beggiatoa spp. represent novel phylogenetic clusters distinct from previously sequenced, large marine Beggiatoa spp. and Thioploca spp. Fluorescence in situ hybridization (FISH) of the natural Beggiatoa spp. populations showed that filament width is a conservative character of each phylogenetic species but a given filament width may represent multiple phylogenetic species in a mixed population.     

Use of Reduced Sulfur Compounds by Beggiatoa spp.: Enzymology and Physiology of Marine and Freshwater Strains in Homogeneous and Gradient Cultures

The marine Beggiatoa strains MS-81-6 and MS-81-1c are filamentous, gliding, colorless sulfur bacteria. They have traditionally been cultured in very limited quantities in sulfide gradient media, where they grow as chemolithoautotrophs, forming a thin horizontal plate well below the air-agar interface. There, the facultatively chemolithoautotrophic strain MS-81-6 quantitatively harvests the flux of sulfide diffusing from below and oxidizes it to sulfate by using oxygen as the electron acceptor. Only recently have these strains been cultivated in bulk in defined liquid media (K. D. Hagen and D. C. Nelson, Appl. Environ. Microbiol. 62:947-953, 1996). In the current study, the obligately chemolithoautotrophic strain MS-81-1c was shown to have, despite much greater storage of elemental sulfur, an apparent Y(infH)(inf(inf2))(infS) twice that of MS-81-6 when the two strains were grown in identical sulfide-limited gradient media. While the basis of this difference in energy conservation has not been established, differences in sulfur oxidation enzymes were noted. Strain MS-81-1c appeared to be able to oxidize sulfite by using either the adenosine phosphosulfate (APS) pathway or a sulfite:acceptor oxidoreductase. APS pathway enzymes (ATP sulfurylase and APS reductase) were present at relatively high and constant levels regardless of growth conditions, while the sulfite:acceptor oxidoreductase activity varied at least eightfold, with the highest activity produced in sulfide gradient medium. By contrast, strain MS-81-6 showed no detectable activity of the APS pathway enzymes and possessed a sulfite:acceptor oxidoreductase activity just sufficient to account for its observed rate of growth in sulfide gradient medium. Freshwater strain OH-75-2a showed activity and regulation of sulfite:acceptor oxidoreductase consistent with lithotrophic energy conservation, a feature not yet proven for any freshwater Beggiatoa strain.     

Colorless Sulfur Bacteria, Beggiatoa spp. and Thiovulum spp., in O(2) and H(2)S Microgradients

The interactions between colorless sulfur bacteria and the chemical microgradients at the oxygen-sulfide interface were studied in Beggiatoa mats from marine sediments and in Thiovulum veils developing above the sediments. The gradients of O(2), H(2)S, and pH were measured by microelectrodes at depth increments of 50 mum. An unstirred boundary layer in the water surrounding the mats and veils prevented microturbulent or convective mixing of O(2) and H(2)S. The two substrates reached the bacteria only by molecular diffusion through the boundary layer. The bacteria lived as microaerophiles or anaerobes even under stirred, oxic water. Oxygen and sulfide zones overlapped by 50 mum in the bacterial layers. Both compounds had concentrations in the range of 0 to 10 mumol liter and residence times of 0.1 to 0.6 s in the overlapping zone. The sulfide oxidation was purely biological. Diffusion calculations showed that formation of mats on solid substrates or of veils in the water represented optimal strategies for the bacteria to achieve a stable microenvironment, a high substrate supply, and an efficient competition with chemical sulfide oxidation. The continuous gliding movement of Beggiatoa cells in mats or the flickering motion of Thiovulum cells in veils were important for the availability of both O(2) and H(2)S for the individual bacteria.     

Physiological adaptation of a nitrate-storing Beggiatoa sp. to diel cycling in a phototrophic hypersaline mat

The aim of this study was to investigate the supposed vertical diel migration and the accompanying physiology of Beggiatoa bacteria from hypersaline microbial mats. We combined microsensor, stable-isotope, and molecular techniques to clarify the phylogeny and physiology of the most dominant species inhabiting mats of the natural hypersaline Lake Chiprana, Spain. The most dominant morphotype had a filament diameter of 6 to 8 microm and a length varying from 1 to >10 mm. Phylogenetic analysis by 16S rRNA gene comparison revealed that this type appeared to be most closely related (91% sequence identity) to the narrow (4-microm diameter) nonvacuolated marine strain MS-81-6. Stable-isotope analysis showed that the Lake Chiprana species could store nitrate intracellularly to 40 mM. The presence of large intracellular vacuoles was confirmed by fluorescein isothiocyanate staining and subsequent confocal microscopy. In illuminated mats, their highest abundance was found at a depth of 8 mm, where oxygen and sulfide co-occurred. However, in the dark, the highest Beggiatoa densities occurred at 7 mm, and the whole population was present in the anoxic zone of the mat. Our findings suggest that hypersaline Beggiatoa bacteria oxidize sulfide with oxygen under light conditions and with internally stored nitrate under dark conditions. It was concluded that nitrate storage by Beggiatoa is an optimal strategy to both occupy the suboxic zones in sulfidic sediments and survive the dark periods in phototrophic mats.     

Impact of bacterial NO3(-) transport on sediment biogeochemistry

Experiments demonstrated that Beggiatoa could induce a H2S-depleted suboxic zone of more than 10 mm in marine sediments and cause a divergence in sediment NO3(-) reduction from denitrification to dissimilatory NO3(-) reduction to ammonium. pH, O2, and H2S profiles indicated that the bacteria oxidized H2S with NO3(-) and transported S0 to the sediment surface for aerobic oxidation.     

High Nitrate Concentrations in Vacuolate, Autotrophic Marine Beggiatoa spp

Massive accumulations of very large Beggiatoa spp. are found at a Monterey Canyon cold seep and at Guaymas Basin hydrothermal vents. Both environments are characterized by high sediment concentrations of soluble sulfide and low levels of dissolved oxygen in surrounding waters. These filamentous, sulfur-oxidizing bacteria accumulate nitrate intracellularly at concentrations of 130 to 160 mM, 3,000- to 4,000-fold higher than ambient levels. Average filament widths range from 24 to 122 (mu)m, and individual cells of all widths possess a central vacuole. These findings plus recent parallel discoveries for Thioploca spp. (H. Fossing, V. A. Gallardo, B. B. Jorgensen, M. Huttel, L. P. Nielsen, H. Schulz, D. E. Canfield, S. Forster, R. N. Glud, J. K. Gundersen, J. Kuver, N. B. Ramsing, A. Teske, B. Thamdrup, and O. Ulloa, Nature (London) 374:713-715, 1995) suggest that nitrate accumulation may be a universal property of vacuolate, filamentous sulfur bacteria. Ribulose bisphosphate carboxylase-oxygenase and 2-oxoglutarate dehydrogenase activities in the Beggiatoa sp. from Monterey Canyon suggest in situ autotrophic growth of these bacteria. Nitrate reductase activity is much higher in the Monterey Beggiatoa sp. than in narrow, laboratory-grown strains of Beggiatoa spp., and the activity is found primarily in the membrane fraction, suggesting that the vacuolate Beggiatoa sp. can reduce nitrate coupled to electron flow through an electron transport system. Nitrate-concentrating and respiration potentials of these chemolithoautotrophs suggest that the Beggiatoa spp. described here are an important link between the sulfur, nitrogen, and carbon cycles at the Monterey Canyon seeps and the Guaymas Basin hydrothermal vents where they are found.     

Ecology of the bacteria of the sulphur cycle with special reference to anoxic-oxic interface environments

H2S is produced as a main end-product of anaerobic mineralization in anoxic, sulphate-rich environments by a diverse population of sulphate-reducing bacteria. The sulphate reducers can carry out an almost complete oxidation of detrital organic matter to CO2. The H2S consequently becomes an important electron carrier from the anoxic to the oxic world. Thiobacilli and other colourless sulphur bacteria have the potential to oxidize the H2S at the oxic-anoxic interface in sediments or stratified waters, but their role is still poorly understood. A comparison of sulphide oxidation processes in the chemoclines of the Black Sea, the Solar Lake and in A beggiatoa mat indicated that depth scales and retention times of coexisting O2 and H2S regulate the bacterial involvement in the sulphide oxidation. The H2S specialists, Beggiatoa and Thiovulum, are optimally adapted to compete with the autocatalytic oxidation of H2S by O2. Microelectrode measurements show retention times of O2-H2S in the bacterial mats or veils of less than 1 s. In photic chemoclines of stratified waters or sulfureta, the phototrophic sulphur bacteria or cyanobacteria interact with the sulphide oxidation at the O2-H2S interface. Short cycles between H2S and intermediate oxidation products, So or S2O2 3-, are created. The bacteria of the sulfuretum are highly adapted to the diurnal rhythm of light, O2 and H2S.     

Competition for sulfide among colorless and purple sulfur bacteria in cyanobacterial mats

Abstract The vertical zonation of light, O₂, H₂S, pH, and sulfur bacteria was studied in two benthic cyanobacterial mats from hypersaline ponds at Guerrero Negro, baja California, Mexico. The physical-chemical gradients were analyzed in the upper few mm at ≥ 100 μm spatial resolution by microelectrodes and by a fiber optic microprobe. In mats, where oxygen produced by photosynthesis diffused far below the depth of the photic zone, colorless sulfur bacteria ( Beggiatoa sp.) were the dominant sulfide oxidizing organisms. In a mat, where the O₂–H₂S interface was close to the photic zone, but yet received no significant visible light, purple sulfur bacteria ( Chromatium sp.) were the dominant sulfide oxidizers. Analysis of the spectral light distribution heare showed that the penetration of only 1% of the incident near-IR light (800–900 nm) into the sulfide zone was sufficient for the development of Chromatium in a narrow band of 300 μm thickness. The balance betweem O₂ and light penetration down into the sulfide zone thus deterined in mcro-scale which type of sulfur bacteria becamed dominant.     

Low temperature S(0) biomineralization at a supraglacial spring system in the Canadian High Arctic

Elemental sulfur (S(0) ) is deposited each summer onto surface ice at Borup Fiord pass on Ellesmere Island, Canada, when high concentrations of aqueous H(2) S are discharged from a supraglacial spring system. 16S rRNA gene clone libraries generated from sulfur deposits were dominated by β-Proteobacteria, particularly Ralstonia sp. Sulfur-cycling micro-organisms such as Thiomicrospira sp., and ε-Proteobacteria such as Sulfuricurvales and Sulfurovumales spp. were also abundant. Concurrent cultivation experiments isolated psychrophilic, sulfide-oxidizing consortia, which produce S(0) in opposing gradients of Na(2) S and oxygen. 16S rRNA gene analyses of sulfur precipitated in gradient tubes show stable sulfur-biomineralizing consortia dominated by Marinobacter sp. in association with Shewanella, Loktanella, Rubrobacter, Flavobacterium, and Sphingomonas spp. Organisms closely related to cultivars appear in environmental 16S rRNA clone libraries; none currently known to oxidize sulfide. Once consortia were simplified to Marinobacter and Flavobacteria spp. through dilution-to-extinction and agar removal, sulfur biomineralization continued. Shewanella, Loktanella, Sphingomonas, and Devosia spp. were also isolated on heterotrophic media, but none produced S(0) alone when reintroduced to Na(2) S gradient tubes. Tubes inoculated with a Marinobacter and Shewanella spp. co-culture did show sulfur biomineralization, suggesting that Marinobacter may be the key sulfide oxidizer in laboratory experiments. Light, florescence and scanning electron microscopy of mineral aggregates produced in Marinobacter experiments revealed abundant cells, with filaments and sheaths variably mineralized with extracellular submicron sulfur grains; similar biomineralization was not observed in abiotic controls. Detailed characterization of mineral products associated with low temperature microbial sulfur-cycling may provide biosignatures relevant to future exploration of Europa and Mars.     

Effect of nitrite and nitrate on in situ sulfide production in an activated sludge immobilized agar gel film as determined by use of microelectrodes

Microelectrode, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) analyses were used to investigate the effect of nitrite and nitrate on in situ sulfide production in an activated sludge immobilized agar gel film. Microelectrode measurements of O(2), H(2)S, NO(3)(-), NO(2)(-), and pH revealed that the addition of NO(2)(-) and NO(3)(-) forced sulfate reduction zones deeper in the agar gel and significantly reduced the in situ sulfide production levels. The sulfate reduction zone was consequently separated from O(2) and NO(2)(-) or NO(3)(-) respiration zones with increasing the concentrations of NO(2)(-) and NO(3)(-). These NO(2)(-) and NO(3)(-) treatments had only a transient effect on sulfide production. The in situ sulfide production quickly recovered to the previous levels when NO(2)(-) and NO(3)(-) were removed. The PCR-DGGE and FISH analyses revealed that 2-day-continuous addition of 500 microM NO(3)(-) did not change the metabolically active sulfate-reducing bacterial (SRB) community. On the basis of these data, it could be concluded that the addition of NO(2)(-) and NO(3)(-) did not kill SRB, but induced the interspecies competition for common carbon source (i.e., acetate) between nitrate-reducing heterotrophic bacteria and SRB and enhanced the oxidation of the produced sulfide, which were main possible causes of the suppression of in situ sulfide production in the agar gel.     

Denitrification at extremely high pH values by the alkaliphilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium Thioalkalivibrio denitrificans strain ALJD

Thioalkalivibrio denitrificans is the first example of an alkaliphilic, obligately autotrophic, sulfur-oxidizing bacterium able to grow anaerobically by denitrification. It was isolated from a Kenyan soda lake with thiosulfate as electron donor and N2O as electron acceptor at pH 10. The bacterium can use nitrite and N2O, but not nitrate, as electron acceptors during anaerobic growth on reduced sulfur compounds. Nitrate is only utilized as nitrogen source. In batch culture at pH 10, rapid growth was observed on N2O as electron acceptor and thiosulfate as electron donor. Growth on nitrite was only possible after prolonged adaptation of the culture to increasing nitrite concentrations. In aerobic thiosulfate-limited chemostats, Thioalkalivibrio denitrificans strain ALJD was able to grow between pH values of 7.5 and 10.5 with an optimum at pH 9.0. Growth of the organism in continuous culture on N2O was more stable and faster than in aerobic cultures. The pH limit for growth on N2O was 10.6. In nitrite-limited chemostat culture, growth was possible on thiosulfate at pH 10. Despite the observed inhibition of N2O reduction by sulfide, the bacterium was able to grow in sulfide-limited continuous culture with N2O as electron acceptor at pH 10. The highest anaerobic growth rate with N2O in continuous culture at pH 10 was observed with polysulfide (S8(2-)) as electron donor. Polysulfide was also the best substrate for oxygen-respiring cells. Washed cells at pH 10 oxidized polysulfide to sulfate via elemental sulfur in the presence of N2O or O2. In the absence of the electron acceptors, elemental sulfur was slowly reduced which resulted in regeneration of polysulfide. Cells of strain ALJD grown under anoxic conditions contained a soluble cd1-like cytochrome and a cytochrome-aa3-like component in the membranes.     

Organic Carbon Utilization by Obligately and Facultatively Autotrophic Beggiatoa Strains in Homogeneous and Gradient Cultures

Marine Beggiatoa strains MS-81-6 and MS-81-1c are filamentous gliding bacteria that use hydrogen sulfide and thiosulfate as electron donors for chemolithotrophic energy generation. They are known to be capable of chemolithoautotrophic growth in sulfide gradient media; here we report the first successful bulk cultivation of these strains in a defined liquid medium. To investigate their nutritional versatilities, strains MS-81-6 and MS-81-1c were grown in sulfide-oxygen gradient media supplemented with single organic compounds. Respiration rates and biomass production relative to those of controls grown in unsupplemented sulfide-limited media were monitored to determine whether organic compounds were utilized as sources of energy and/or cell carbon. With cells grown in sulfide gradient and liquid media, we showed that strain MS-81-6 strongly regulates two enzymes, the tricarboxylic acid cycle enzyme 2-oxoglutarate dehydrogenase and the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, in response to the presence of organic carbon (acetate) in the growth medium. In contrast, strain MS-81-1c lacked 2-oxoglutarate dehydrogenase activity and regulated ribulose-1,5-bisphosphate carboxylase/oxygenase activity only slightly in response to organic substrates. Tracer experiments with radiolabeled acetate showed that strain MS-81-1c did not oxidize acetate to CO(inf2) but could synthesize approximately 20% of its cell carbon from acetate. On the basis of these results, we conclude that Beggiatoa strain MS-81-1c is an obligate chemolithoautotroph, while strain MS-81-6 is a versatile facultative chemolithoautotroph.     

Tyrosine nitration by peroxynitrite formed from nitric oxide and superoxide generated by xanthine oxidase

Peroxynitrite (ONOO(-)) is a potent nitrating and oxidizing agent that is formed by a rapid reaction of nitric oxide (NO) with superoxide anion (O(2)). It appears to be involved in the pathophysiology of many inflammatory and neurodegenerative diseases. It has recently been reported (Pfeiffer, S., and Mayer, B. (1998) J. Biol. Chem. 273, 27280-27285) that ONOO(-) generated at neutral pH from NO and O(2) (NO/O(2)) was substantially less efficient than preformed ONOO(-) at nitrating tyrosine. Here we re-evaluated tyrosine nitration by NO/O(2) with a shorter incubation period and a more sensitive electrochemical detection system. Appreciable amounts of nitrotyrosine were produced by ONOO(-) formed in situ (2.9 micrometer for 5 min; 10 nm/s) by NO/O(2) flux obtained from propylamine NONOate (CH(3)N[N(O)NO](-) (CH(2))(3)NH(2)(+)CH(3)) and xanthine oxidase using pterin as a substrate in phosphate buffer (pH 7.0) containing 0.1 mm l-tyrosine. The yield of nitrotyrosine by this NO/O(2) flux was approximately 70% of that produced by the same flux of preformed ONOO(-) (2.9 micrometer/5 min). When hypoxanthine was used as a substrate, tyrosine nitration by NO/O(2) was largely eliminated because of the inhibitory effect of uric acid produced during the oxidation of hypoxanthine. Tyrosine nitration caused by NO/O(2) was inhibited by the ONOO(-) scavenger ebselen and was enhanced 2-fold by NaHCO(3), as would be expected, because CO(2) promotes tyrosine nitration. The profile of nitrotyrosine and dityrosine formation produced by NO/O(2) flux (2.9 micrometer/5 min) was consistent with that produced by preformed ONOO(-). Tyrosine nitration predominated compared with dityrosine formation caused by a low nanomolar flux of ONOO(-) at physiological concentrations of free tyrosine (<0.5 mm). In conclusion, our results show that NO generated with O(2) nitrates tyrosine with a reactivity and efficacy similar to those of chemically synthesized ONOO(-), indicating that ONOO(-) can be a significant source of tyrosine nitration in physiological and pathological events in vivo.     

Sulfur Production by Obligately Chemolithoautotrophic Thiobacillus Species

Transient-state experiments with the obligately autotrophic Thiobacillus sp. strain W5 revealed that sulfide oxidation proceeds in two physiological phases, (i) the sulfate-producing phase and (ii) the sulfur- and sulfate-producing phase, after which sulfide toxicity occurs. Specific sulfur-producing characteristics were independent of the growth rate. Sulfur formation was shown to occur when the maximum oxidative capacity of the culture was approached. In order to be able to oxidize increasing amounts of sulfide, the organism has to convert part of the sulfide to sulfur (HS(sup-)(symbl)S(sup0) + H(sup+) + 2e(sup-)) instead of sulfate (HS(sup-) + 4H(inf2)O(symbl)SO(inf4)(sup2-) + 9 H(sup+) + 8e(sup-)), thereby keeping the electron flux constant. Measurements of the in vivo degree of reduction of the cytochrome pool as a function of increasing sulfide supply suggested a redox-related down-regulation of the sulfur oxidation rate. Comparison of the sulfur-producing properties of Thiobacillus sp. strain W5 and Thiobacillus neapolitanus showed that the former has twice the maximum specific sulfide-oxidizing capacity of the latter (3.6 versus 1.9 (mu)mol/mg of protein/min). Their maximum specific oxygen uptake rates were very similar. Significant mechanistic differences in sulfur production between the high-sulfur-producing Thiobacillus sp. strain W5 and the moderate-sulfur-producing species T. neapolitanus were not observed. The limited sulfide-oxidizing capacity of T. neapolitanus appears to be the reason that it can convert only 50% of the incoming sulfide to elemental sulfur.     

Thermothrix thioparus gen. et sp. nov. a facultatively anaerobic facultative chemolithotroph living at neutral pH and high temperature.

Thermothrix thioparus gen. et ep. nov. occurs naturally in a New Mexico hot spring at a temperature of 74 degrees C, a pH of 7.0, and a HS- concentration of 1 mg/litre. The organism is gram-negative, non-motile, 0.5-1.0 X 3-20 mum, and forms cell chains up to 1 cm in length. The resulting filaments do not possess a sheath. Sulfur is deposited extracellularly. The organism was isolated using an autotrophic medium with HS- as the energy source and NO3- as the terminal electron acceptor. Anaerobically either NO2- or NO3- is required, NO2- is formed from NO3-, and no observable gas is evolved. Oxygen can also be used as the terminal electron acceptor, but growth is poor because of the decreased solubility of O2 at temperatures required for growth. Alternate energy sources used aerobically and anaerobically include hexose, HS-, SO3-, and S2O3=. The temperature optimum is 70-73 degrees C and growth occurs from 62 to 77 degrees C. The organism's thermal and physiological characteristics are compared to those of Bacillus stearothermophilus, Methanobacterium thermoautotrophicum, Sulfolobus acidocalderius, Thermus aquaticus, Thermus flavus, as well as Thiobacillus denitrificans, the latter being the only other facultatively anaerobic chemolithotroph which has been isolated and described.     

Inhibition by sulfide of nitric and nitrous oxide reduction by denitrifying Pseudomonas fluorescens.

The influence of low redox potentials and H2S on NO and N2O reduction by resting cells of denitrifying Pseudomonas fluorescens was studied. Hydrogen sulfide and Ti(III) were added to achieve redox potentials near -200 mV. The control without reductant had a redox potential near +200 mV. Production of 13NO, [13N]N2O, and [13N]N2 from 13NO3- and 13NO2- was followed. Total gas production was similar for all three treatments. The accumulation of 13NO was most significant in the presence of sulfide. A parallel control with autoclaved cells indicated that the 13NO production was largely biological. The sulfide inhibition was more dramatic at the level of N2O reduction; [13N]N2O became the major product instead of [13N]N2, the dominant product when either no reductant or Ti(III) was present. The results indicate that the specific action of sulfide rather than the low redox potential caused a partial inhibition of NO reduction and a strong inhibition of N2O reduction in denitrifying cells.     

Oxygen and sulfide dynamics in a horizontally migrating cyanobacterial mat: Black band disease of corals

Abstract: Black band disease is caused by a horizontally migrating microbial consortium which overgrows and kills reef-building corals in many areas of the world. The cyanobacterium Phormidium corallyticum , the sulfide-oxidizing bacterium Beggiatoa sp., fungi, and sulfate-reducing bacteria dominate the consortium, which is generally several mm to 1 cm in width and ca. 1 mm in thickness. Microelectrode measurements revealed photosynthetically produced O₂-supersaturation in upper layers during day, although conditions at the band-coral interface were consistently anoxic and, at night, sulfide-rich. Diel distributions of oxygen and sulfide resembled those from cyanobacterial mats in sulfur springs, intertidal mats and hypersaline lagoons.     

A highly purified enrichment culture couples the reductive dechlorination of tetrachloroethene to growth.

A microscopically pure enrichment culture of a gram-negative anaerobic bacterium, in the present article referred to as PER-K23, was isolated from an anaerobic packed-bed column in which tetrachloroethene (PCE) was reductively transformed to ethane via trichloroethene (TCE), cis-1,2-dichloroethene (cis-1,2-DCE), chloroethene, and ethene. PER-K23 catalyzes the dechlorination of PCE via TCE to cis-1,2-DCE and couples this reductive dechlorination to growth. H2 and formate were the only electron donors that supported growth with PCE or TCE as an electron acceptor. The culture did not grow in the absence of PCE or TCE. Neither O2, NO3-, NO2-, SO4(2-), SO3(2-), S2O3(2-), S, nor CO2 could replace PCE or TCE as an electron acceptor with H2 as an electron donor. Also, organic electron acceptors such as acetoin, acetol, dimethyl sulfoxide, fumarate, and trimethylamine N-oxide and chlorinated ethanes, DCEs, and chloroethene were not utilized. PER-K23 was not able to grow fermentatively on any of the organic compounds tested. Transferring the culture to a rich medium revealed that a contaminant was still present. Dechlorination was optimal between pH 6.8 and 7.6 and a temperature of 25 to 35 degrees C. H2 consumption was paralleled by chloride production, PCE degradation, cis-1,2-DCE formation, and growth of PER-K23. Electron balances showed that all electrons derived from H2 or formate consumption were recovered in dechlorination products and biomass. Exponential growth could be achieved only in gently shaken cultures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of a novel biocatalyst system for sulfide oxidation

It has been demonstrated that an enrichment culture dominated by Thiomicrospira sp. CVO may be cultured on H2S(g) as an energy source under sulfide-limiting conditions in suspended culture with nitrate as the electron acceptor. Hydrogen sulfide (10,000 ppmv) was completely removed from the feed gas and oxidized to sulfate in <3 s of gas-liquid contacting time. Maximum loading of the biomass for sulfide oxidation was observed to be 5.8 mmol H2S/h-g biomass protein, comparable to that reported previously for Thiobacillus denitrificans under similar conditions. However, the enrichment culture was shown to be more tolerant of extremes in pH and elevated temperature than T. denitrificans. Coupled with a reported tolerance of CVO for up to 10% NaCl, these observations suggest that a CVO-based culture is potentially a more robust biocatalyst system for sulfide oxidation than cultures based on Thiobacilli.