Behaviour of toluene, benzene and naphthalene under anaerobic conditions in sediment columns

The biotransformation of toluene, benzene and naphthalene was examined in anaerobic sediment columns. Five columns filled with a mixture of sediments were operated in the presence of bicarbonate, sulfate, iron, manganese, or nitrate as electron acceptor. The columns were continuously percolated with a mixture of the three organic compounds (individual concentrations 25–200 M) at 20°C.Toluene was transformed readily (within 1 to 2 months) under all redox conditions tested. Benzene was recalcitrant over the test period of 375–525 days in all five columns. Naphthalene was partly transformed in the column with nitrate or manganese as electron acceptor present; the addition of benzoate had a positive effect in the column with nitrate. In the column with sulfate, the majority of the added naphthalene disappeared. No effect was observed after adding and omitting an easier degradable substrate. [¹⁴C]naphthalene was used to confirm this disappearance to be the result of degradation; two third of the naphthalene was converted to CO₂.     

Benzene oxidation under sulfate-reducing conditions in columns simulating in situ conditions

The oxidation of benzene under sulfate-reducing conditions was examined in column and batch experiments under close to in situ conditions. Mass balances and degradation rates for benzene oxidation were determined in four sand and four lava granules filled columns percolated with groundwater from an anoxic benzene-contaminated aquifer. The stoichiometry of oxidized benzene, produced hydrogen carbonate and reduced sulfate correlated well with the theoretical equation for mineralization of benzene with sulfate as electron acceptor. Mean retention times of water in four columns were determined using radon (²²²Rn) as tracer. The retention times were used to calculate average benzene oxidation rates of 8–36 μM benzene day⁻¹. Benzene-degrading, sulfide-producing microcosms were successfully established from sand material of all sand filled columns, strongly indicating that the columns were colonized by anoxic benzene-degrading microorganisms. In general, these data indicate a high potential for Natural Attenuation of benzene under sulfate-reducing conditions at the field site Zeitz. In spite of this existing potential to degrade benzene with sulfate as electron acceptor, the benzene plume at the field site is much longer than expected if benzene would be degraded at the rates observed in the column experiment, indicating that benzene oxidation under sulfate-reducing conditions is limited in situ.     

Chemolithotrophic growth ofDesulfovibrio desulfuricans with hydrogen coupled to ammonification of nitrate or nitrite

Two of nine sulfate reducing bacteria tested,Desulfobulbus propionicus andDesulfovibrio desulfuricans (strain Essex 6), were able to grow with nitrate as terminal electron acceptor, which was reduced to ammonia. Desulfovibrio desulfuricans was grown in chemostat culture with hydrogen plus limiting concentrations of nitrate, nitrite or sulfate as sole energy source. Growth yields up to 13.1, 8.8 or 9.7 g cell dry mass were obtained per mol nitrate, nitrite or sulfate reduced, respectively. The apparent half saturation constants (K _s) were below the detection limits of 200, 3 or 100 mol/l for nitrate, nitrite of sulfate, respectively. The maximum growth rates {ie63-1} raised from 0.124 h^-1 with sulfate and 0.150 h^-1 with nitrate to 0.193 h^-1 with nitrite as electron acceptor. Regardless of the electron acceptor in the culture medium, cell extracts exhibited absorption maxima corresponding to cytochromec and desulfoviridin. Nitrate reductase was found to be inducible by nitrate or nitrite, whereas nitrite reductase was synthesized constitutively. The activities of nitrate and nitrite reductases with hydrogen as electron donor were 0.2 and 0.3 mol/min·mg protein, respectively. If limiting amounts of hydrogen were added to culture bottles with nitrate as electron acceptor, part of the nitrate was only reduced to the level of nitrite. In media containing nitrate plus sulfate or nitrite plus sulfate, sulfate reduction was suppressed.The results demonstrate that the ammonification of nitrate or nitrite can function as sole energy conserving process in some sulfate-reducing bacteria.     

Anaerobic biodegradation of no. 2 diesel fuel in soil: a soil column study

Soil and sediments are contaminated with petroleum hydrocarbons in many parts of the world. Anaerobic degradation of petroleum hydrocarbon is very relevant in removing oil spills in the anaerobic zones of soil and sediments. This research investigates the possibility of degrading no. diesel fuel under anaerobic conditions. Anaerobic packed soil columns were used to simulate and study in situ bioremediation of soil contaminated with diesel fuel. Several anaerobic conditions were evaluated in soil columns, including sulfate reducing, nitrate reducing, methanogenic, and mixed electron acceptor conditions. The objectives were to determine the extent of diesel fuel degradation in soil columns under various anaerobic conditions and identify the best conditions for efficient removal of diesel fuel. Diesel fuels were degraded significantly under all conditions compared to no electron supplemented soil column (natural attenuation). However, the rate of diesel degradation was the highest under mixed electron acceptor conditions followed in order by sulfate reducing, nitrate reducing, and methanogenic conditions. Under mixed electron acceptor condition 81% of diesel fuel was degraded within 310 days. While under sulfate reducing condition 54.5% degradation of diesel fuel was observed for the same period. This study showed evidence for diesel fuel metabolism in a mixed microbial population system similar to any contaminated field sites, where heterogeneous microbial population exists.     

Stimulating the anaerobic degradation of aromatic hydrocarbons in contaminated sediments by providing an electrode as the electron acceptor

The possibility that electrodes might serve as an electron acceptor to simulate the degradation of aromatic hydrocarbons in anaerobic contaminated sediments was investigated. Initial studies with Geobacter metallireducens demonstrated that although toluene was rapidly adsorbed onto the graphite electrodes it was rapidly oxidized to carbon dioxide with the electrode serving as the sole electron acceptor. Providing graphite electrodes as an electron acceptor in hydrocarbon‐contaminated sediments significantly stimulated the removal of added toluene and benzene. Rates of toluene and benzene removal accelerated with continued additions of toluene and benzene. [¹⁴C]‐Toluene and [¹⁴C]‐benzene were quantitatively recovered as [¹⁴C]‐CO₂, demonstrating that even though the graphite adsorbed toluene and benzene they were degraded. Introducing an electrode as an electron acceptor also accelerated the loss of added naphthalene and [¹⁴C]‐naphthalene was converted to [¹⁴C]‐CO₂. The results suggest that graphite electrodes can serve as an electron acceptor for the degradation of aromatic hydrocarbon contaminants in sediments, co‐localizing the contaminants, the degradative organisms and the electron acceptor. Once in position, they provide a permanent, low‐maintenance source of electron acceptor. Thus, graphite electrodes may offer an attractive alternative for enhancing contaminant degradation in anoxic environments.     

Anaerobic Naphthalene Degradation by a Sulfate-Reducing Enrichment Culture

Anaerobic naphthalene degradation by a sulfate-reducing enrichment culture was studied by substrate utilization tests and identification of metabolites by gas chromatography-mass spectrometry. In substrate utilization tests, the culture was able to oxidize naphthalene, 2-methylnaphthalene, 1- and 2-naphthoic acids, phenylacetic acid, benzoic acid, cyclohexanecarboxylic acid, and cyclohex-1-ene-carboxylic acid with sulfate as the electron acceptor. Neither hydroxylated 1- or 2-naphthoic acid derivatives and 1- or 2-naphthol nor the monoaromatic compounds ortho-phthalic acid, 2-carboxy-1-phenylacetic acid, and salicylic acid were utilized by the culture within 100 days. 2-Naphthoic acid accumulated in all naphthalene-grown cultures. Reduced 2-naphthoic acid derivatives could be identified by comparison of mass spectra and coelution with commercial reference compounds such as 1,2,3,4-tetrahydro-2-naphthoic acid and chemically synthesized decahydro-2-naphthoic acid. 5,6,7,8-Tetrahydro-2-naphthoic acid and octahydro-2-naphthoic acid were tentatively identified by their mass spectra. The metabolites identified suggest a stepwise reduction of the aromatic ring system before ring cleavage. In degradation experiments with [1-¹³C]naphthalene or deuterated D₈-naphthalene, all metabolites mentioned derived from the introduced labeled naphthalene. When a [¹³C]bicarbonate-buffered growth medium was used in conjunction with unlabeled naphthalene, ¹³C incorporation into the carboxylic group of 2-naphthoic acid was shown, indicating that activation of naphthalene by carboxylation was the initial degradation step. No ring fission products were identified.     

Anaerobic Degradation of Benzene, Toluene, Ethylbenzene, and Xylene Compounds by Dechloromonas Strain RCB

Dechloromonas strain RCB has been shown to be capable of anaerobic degradation of benzene coupled to nitrate reduction. As a continuation of these studies, the metabolic versatility and hydrocarbon biodegradative capability of this organism were investigated. The results of these revealed that in addition to nitrate, strain RCB could alternatively degrade benzene both aerobically and anaerobically with perchlorate or chlorate [(per)chlorate] as a suitable electron acceptor. Furthermore, with nitrate as the electron acceptor, strain RCB could also utilize toluene, ethylbenzene, and all three isomers of xylene (ortho-, meta-, and para-) as electron donors. While toluene and ethylbenzene were completely mineralized to CO₂, strain RCB did not completely mineralize para-xylene but rather transformed it to some as-yet-unidentified metabolite. Interestingly, with nitrate as the electron acceptor, strain RCB degraded benzene and toluene concurrently when the hydrocarbons were added as a mixture and almost 92 μM total hydrocarbons were oxidized within 15 days. The results of these studies emphasize the unique metabolic versatility of this organism, highlighting its potential applicability to bioremediative technologies.     

Anaerobic degradation of alkylated benzenes in denitrifying laboratory aquifer columns

Toluene and m-xylene were rapidly mineralized in an anaerobic laboratory aquifer column operated under continuous-flow conditions with nitrate as an electron acceptor. The oxidation of toluene and m-xylene was coupled with the reduction of nitrate, and mineralization was confirmed by trapping 14CO2 evolved from 14C-ring-labeled substrates. Substrate degradation also took place when nitrous oxide replaced nitrate as an electron acceptor, but decomposition was inhibited in the presence of molecular oxygen or after the substitution of nitrate by nitrite. The m-xylene-adapted microorganisms in the aquifer column degraded toluene, benzaldehyde, benzoate, m-toluylaldehyde, m-toluate, m-cresol, p-cresol, and p-hydroxybenzoate but were unable to metabolize benzene, naphthalene, methylcyclohexane, and 1,3-dimethylcyclohexane. Isotope-dilution experiments suggested benzoate as an intermediate formed during anaerobic toluene metabolism. The finding that the highly water-soluble nitrous oxide served as electron acceptor for the anaerobic mineralization of some aromatic hydrocarbons may offer attractive options for the in situ restoration of polluted aquifers.     

Anaerobic degradation of alkylated benzenes in denitrifying laboratory aquifer columns.

Toluene and m-xylene were rapidly mineralized in an anaerobic laboratory aquifer column operated under continuous-flow conditions with nitrate as an electron acceptor. The oxidation of toluene and m-xylene was coupled with the reduction of nitrate, and mineralization was confirmed by trapping 14CO2 evolved from 14C-ring-labeled substrates. Substrate degradation also took place when nitrous oxide replaced nitrate as an electron acceptor, but decomposition was inhibited in the presence of molecular oxygen or after the substitution of nitrate by nitrite. The m-xylene-adapted microorganisms in the aquifer column degraded toluene, benzaldehyde, benzoate, m-toluylaldehyde, m-toluate, m-cresol, p-cresol, and p-hydroxybenzoate but were unable to metabolize benzene, naphthalene, methylcyclohexane, and 1,3-dimethylcyclohexane. Isotope-dilution experiments suggested benzoate as an intermediate formed during anaerobic toluene metabolism. The finding that the highly water-soluble nitrous oxide served as electron acceptor for the anaerobic mineralization of some aromatic hydrocarbons may offer attractive options for the in situ restoration of polluted aquifers.     

Effect of Reduced Sulfur Species on Chemolithoautotrophic Pyrite Oxidation with Nitrate

We compared the response at neutral pH of some denitrifiers to different electron donors such as reduced sulfur (pyrite, S(0), and marcasite) and reduced Fe. Chemolithoautotrophic oxidation of pyrite with nitrate as electron acceptor was not possible when the pyrite was in a pure crystalline form, whereas oxidation of synthesized FeS₂ of low crystallinity and of S(0) with nitrate as electron acceptor was possible. Neither nitrite nor sulfate was formed when Fe(II)-oxidizing strain Acidovorax sp. BoFeN1 was tested. Microbial reduction of nitrate appears to be induced via S oxidation but not via Fe oxidation.     

Control of microbial souring by nitrate,nitrite or glutaraldehyde injection in a sandstone column

Microbial souring (production of hydrogen sulfide by sulfate-reducing bacteria, SRB) in crushed Berea sandstone columns with oil field-produced water consortia incubated at 60°C was inhibited by the addition of nitrate (NO₃) or nitrite (NO ₂ ^– ). Added nitrate (as nitrogen) at a concentration of 0.71 mM resulted in the production of 0.57–0.71 mM nitrite by the native microbial population present during souring and suppressed sulfate reduction to below detection limits. Nitrate added at 0.36 mM did not inhibit active souring but was enough to maintain inhibition if the column had been previously treated with 0.71 mM or greater. Continuous addition of 0.71–0.86 mM nitrite also completely inhibited souring in the column. Pulses of nitrite were more effective than the same amount of nitrite added continuously. Nitrite was more effective at inhibiting souring than was glutaraldehyde, and SRB recovery was delayed longer with nitrite than with glutaraldehyde. It was hypothesized that glutaraldehyde killed SRB while nitrite provided a long-term inhibition without cell death. Removal of nitrate after as long as 3 months of continuous addition allowed SRB in a biofilm to return to their previous level of activity. Inhibition was achieved with much lower levels of nitrate and nitrite, and at higher temperatures, than noted by other researchers.     

Novel Processes for Anaerobic Sulfate Production from Elemental Sulfur by Sulfate-Reducing Bacteria

Sulfate reducers and related organisms which had previously been found to reduce Fe(III) with H₂ or organic electron donors oxidized S⁰ to sulfate when Mn(IV) was provided as an electron acceptor. Organisms catalyzing this reaction in washed cell suspensions included Desulfovibrio desulfuricans, Desulfomicrobium baculatum, Desulfobacterium autotrophicum, Desulfuromonas acetoxidans, and Geobacter metallireducens. These organisms produced little or no sulfate from S⁰ with Fe(III) as a potential electron acceptor or in the absence of an electron acceptor. In detailed studies with Desulfovibrio desulfuricans, the stoichiometry of sulfate and Mn(II) production was consistent with the reaction S⁰ + 3 MnO₂ + 4H⁺→SO₄^2- + 3Mn(II) + 2H₂O. None of the organisms evaluated could be grown with S⁰ as the sole electron donor and Mn(IV) as the electron acceptor. In contrast to the other sulfate reducers evaluated, Desulfobulbus propionicus produced sulfate from S⁰ in the absence of an electron acceptor and Fe(III) oxide stimulated sulfate production. Sulfide also accumulated in the absence of Mn(IV) or Fe(III). The stoichiometry of sulfate and sulfide production indicated that Desulfobulbus propionicus disproportionates S⁰ as follows: 4S⁰ + 4H₂O→SO₄^2- + 3HS^- + 5 H⁺. Growth of Desulfobulbus propionicus with S⁰ as the electron donor and Fe(III) as a sulfide sink and/or electron acceptor was very slow. The S⁰ oxidation coupled to Mn(IV) reduction described here provides a potential explanation for the Mn(IV)-dependent sulfate production that previous studies have observed in anoxic marine sediments. Desulfobulbus propionicus is the first example of a pure culture known to disproportionate S⁰.     

Kinetic coefficients for simultaneous reduction of sulfate and uranium by Desulfovibrio desulfuricans

 Previously it was demonstrated that bacteria are capable of transforming soluble uranyl ion, U(VI), to insoluble uraninite, U(IV); however, the rate for this transformation has not been determined. We report the kinetic coefficients for Desulfovibrio desulfuricans DSM 1924 grown in a continuous-flow chemostat where pyruvate was the electron donor and sulfate was the electron acceptor. The medium was supplemented with 1 mM uranyl nitrate, and the chemostat flow rate ranged from 1.12 ml/h to 4.75 ml/h with incubation at 28°C. The maximum rate of pyruvate utilization (k) was determined to be 4.7 days^-1, while the half-velocity constant (K _s) was 127 mg/l. The yield coefficient (Y) of cells per mole of pyruvate oxidized was calculated to be 0.021 g, while the endogenous decay coefficient (k _d) was determined to be 0.072 days^-1. More than 90% of U(VI) was transformed to U(VI) in the chemostat under the conditions employed. Received: 7 September 1995/Received last revision: 10 January 1996/Accepted: 5 February 1996     

Characterization of microbial souring in Berea‐sand porous medium with a North Sea oil field inoculum

Microbial souring (H₂S production) in porous medium was investigated in an anaerobic upflow porous medium reactor at 60°C using produced waters obtained from the North Sea Ninian oilfield as the inoculum. Multiple carbon sources commonly found in oil field waters (formate, acetate, propionate, iso‐ and n‐butyrates) with inorganic sulfate as the electron acceptor were used as the substrates. Stoichiometry and the rate of souring in the reactor column were calculated. A large proportion of H₂S was trapped in the column as FeS and possibly as a gas phase. Concentration gradients for the substrates (organic acids and sulfate) and H₂S were generated along the column. At steady state, the highest volumetric substrate consumption and H₂S production were found at the front part (inlet) of the reactor column. The average volumetric sulfate reduction rate after H₂S production had stabilized was calculated to be 203 ± 51 mg sulfate‐S.l^‐1.d^‐1. Comparison of the results with the authors’ previous work on the Alaska Kuparuk oilfield waters indicates that the two different microbial inocula (produced waters) exhibited the same experimental trends (rates and location) for souring in the experimental reactor system. This indicates that abiotic factors, as well as microbial parameters, may play an important role for microbial souring in the system.     

Rapid Microbial Mineralization of Toluene and 1,3-Dimethylbenzene in the Absence of Molecular Oxygen

Up to 0.4 mM 1,3-dimethylbenzene (m-xylene) was rapidly mineralized in a laboratory aquifer column operated in the absence of molecular oxygen with nitrate as an electron acceptor. Under continuous flow conditions, the degradation rate constant (pseudo-first order) was >0.45 h⁻¹. Based on a carbon mass balance with [ring-¹⁴C]m-xylene and a calculation of the electron balance, m-xylene was shown to be quantitatively (80%) oxidized to CO₂ with a concomitant reduction of nitrate. The mineralization of m-xylene in the column also took place after reducing the redox potential, E′, of the inflowing medium with sulfide to <−0.11 V. Microorganisms adapted to growth on m-xylene were also able to degrade toluene under denitrifying conditions. These results suggest that aromatic hydrocarbons present in anoxic environments such as lake sediments, sludge digestors, and groundwater infiltration zones from landfills and polluted rivers are not necessarily persistent but may be mineralized in the absence of molecular oxygen.     

<Emphasis Type="Italic">Thermosulfurimonas marina</Emphasis> sp. nov., an Autotrophic Sulfur-Disproportionating and Nitrate-Reducing Bacterium Isolated from a Shallow-Sea Hydrothermal Vent

A thermophilic, anaerobic, chemolithoautotrophic bacterium (strain SU872^T) was isolated from a shallow-sea hydrothermal vent at Kunashir Island. The cells were motile, gram-negative, oval or rodshaped 0.5?0.6 μm thick and 1.5?2.0 μm long, occurring singly or in pairs. Strain SU872^T grew at 50 to 79°C (optimum at 74°C), pH from 5.0 to 8.0 (optimum at 6.7?7.0), and NaCl concentration of 1.5–4.5%. Strain SU872^T was able to grow by disproportionation of elemental sulfur, thiosulfate, or sulfite, with CO₂/HCO₃^? as the sole carbon source. Growth was enhanced in the presence of ferrihydrite (poorly crystalline Fe(III) oxide) as as a sulfide-scavenging agent. Sulfate was not used as an electron acceptor. Growth also occurred with elemental sulfur, thiosulfate, or sulfite (but not sulfide) as electron donors and nitrate as an electron acceptor, with production of sulfate and ammonium. Analysis of the 16S rRNA gene sequence revealed 97.8% similarity between strain SU872^T and the type strain Thermosulfurimonas dismutans S95^T (phylum Thermodesulfobacteria). According to the results of DNA–DNA hybridization, the similarity of genomic DNA of the strains SU872^T and T. dismutans S95^T was 48%. Based on its phenotypic characteristics and the results of phylogenetic analysis, it is proposed to assign the isolate to a new species of the genus Thermosulfurimonas,—Thermosulfurimonas marina sp. nov., with the type strain SU872^T (=DSM 104922^T, =VKM B-3177^T, =UNIQEM SU872^T).     

Desulfovibrio mexicanus sp. nov., a Sulfate-reducing Bacterium Isolated from an Upflow Anaerobic Sludge Blanket (UASB) Reactor Treating Cheese Wastewaters

A mesophilic sulfate-reducing bacterium, designated strain Lup1^T(T=type strain) was isolated from a Mexican UASB digester treating cheese factory wastewater. The non-motile, Gram-negative, curved and non-spore-forming cells (1.7–2.5×0.5 μm) existed singly or in chains. Optimum growth occurred at 37°C and pH 7.2 in a medium containing lactate and thiosulfate. Strain Lup1^Tused pyruvate, formate, Casamino acids, serine, cysteine, H₂and ethanol as electron donors in the presence of thiosulfate as an electron acceptor and fermented pyruvate, Casamino acids, cysteine, and serine. Sulfate, elemental sulfur, and sulfite also served as electron acceptors but not nitrate or fumarate. Thiosulfate was disproportionated to sulfate and sulfide. The G+C content of the DNA was 66 mol%. Phylogenetic analysis based on 16S rDNA revealed that strain Strain Lup1^Twas a member of the genus Desulfovibrio withDesulfovibrio aminophilus being the closest relative (similarity value of 91%). As strain Lup1^Tis physiologically and phylogenetically different from other Desulfovibrio species, it is designated Desulfovibrio mexicanus sp. nov. (=DSM 13116).     

Lebetimonas natsushimae sp. nov., a novel strictly anaerobic,moderately thermophilic chemoautotroph isolated from a deep-sea hydrothermal vent polychaete nest in the Mid-Okinawa Trough

A moderately thermophilic, strictly anaerobic, chemoautotrophic bacterium, designated strain HS1857^T, was isolated from a deep-sea hydrothermal vent at the Noho site in the Mid-Okinawa Trough. Strain HS1857^T grew between 35 and 63 °C (optimum 55 °C), in the presence of 10–55 g l^?1 NaCl (optimum 25 g l^?1), and pH 5.5–7.1 (optimum 6.4). Growth occurred with molecular hydrogen as the electron donor and elemental sulfur, nitrate, or selenate as the electron acceptors. Formate could serve as an alternative electron donor with nitrate as an electron acceptor. During growth with nitrate as the electron acceptor, strain HS1857^T produced ammonium and formed a biofilm. CO₂ was utilized as the sole carbon source. The G + C content of the genomic DNA was 33.2 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain HS1857^T is a member of the order Nautiliales, showing a sequence similarity of 95.0% with Lebetimonas acidiphila Pd55^T. The fatty acid composition was similar to that of L. acidiphila, which was dominated by C_18:0 (47.0%) and C_18:1 (23.7%). Based on the genomic, chemotaxonomic, phenotypic characteristics, the name Lebetimonas natsushimae sp. nov., is proposed. The type strain is HS1857^T (= NBRC 112478^T = DSM 104102^T).     

Growth yields of Desulfotomaculum orientis with hydrogen in chemostat culture

Desulfotomaculum orientis (strain Singapore 1) was grown autotrophically with H₂+CO₂ and sulfate, thiosulfate or sulfite as electron acceptor in sulfide- and pH-controlled continuous culture. Under sulfate-limiting conditions real growth yields of up to 9.7 g cell dry mass per mol sulfate were obtained. Electron acceptor limitation resulted in the excretion of up to 14.5 mmol acetate per liter, formed by reduction of CO₂ with H₂. Acetate production was not coupled to an increase of growth yields: under hydrogen-limiting conditions only 1.6 mmol acetate per liter was produced, and even higher growth yields of up to 12,4 g cell dry mass per mol sulfate were obtained. With thiosulfate or sulfite as electron acceptor growth yields increased up to 17.9 g cell dry mass per mol electron acceptor. Growth yields were not simply correlated with the growth rate, and did not allow the determination of maintenance coefficients and the extrapolation to maximal yields at infinite growth rate (Y ^max). The maximal growth rates (_max) with sulfate and thiosulfate were 0.090 and 0.109 h^-1, respectively, if cells were grown continuously in sulfidostat culture under nonlimiting conditions.The net energy yield of sulfate reduction and the energy requirement for the activation of sulfate by Desulfotomaculum orientis are discussed.     

Relative influence of temperature and electron donor and electron acceptor concentrations on bacterial sulfate reduction in saltmarsh sediment

The relative importance of three environmental variables known to influence the rate of bacterial sulfate reduction was examined using sediment from a saltmarsh pan. The variables investigated were temperature, electron donor concentration, and electron acceptor concentration. Their relative influence on the rate of bacterial sulfate reduction was examined with multiple replicate sediment samples in which the variables were experimentally adjusted. Sulfate reduction rates were measured with³⁵SO ₄ ^2– .The relative importance of each variable to sulfate reduction rate was assessed with multiple regression analysis by calculating the standardized partial regression coefficients, and the results were compared with the ranges of the three variables encountered in the natural sediment. Temperature proved to have the greatest influence, followed by electron donor and electron acceptor concentrations, in that order. The sulfate concentration was shown to have little influence on sulfate reduction rate at seawater concentrations of sulfate, but its effect increased if sulfate concentrations were diminished compared to those of seawater.