Dissimilatory Sulfate- and Sulfur-Reducing Prokaryotes

Summary

Life at high salt concentrations is energetically expensive. The upper salt concentration limit at which different dissimilatory processes occur in nature appears to be determined to a large extent by bioenergetic constraints. The main factors that determine whether a certain type of microorganism can make a living at high salt are the amount of energy generated during its dissimilatory metabolism and the mode of osmotic adaptation used. I here review new data, both from field observations and from the characterization of cultures of new types of prokaryotes growing at high salt concentrations, to evaluate to what extent the theories formulated 12 years ago are still valid, need to be refined, or should be refuted on the basis of the novel information collected. Most data agree well with the earlier theories. Some new observations, however, are not easily explained: the properties of Natranaerobius and other haloalkaliphilic thermophilic fermentative anaerobes, growth of the sulfate-reducing Desulfosalsimonas propionicica with complete oxidation of propionate and Desulfovermiculus halophilus with complete oxidation of butyrate, growth of lactate-oxidizing sulfate reducers related to Desulfonatronovibrio at 346 g l−1 salts at pH 9.8, and occurrence of methane oxidation in the anaerobic layers of Big Soda Lake and Mono Lake.

Thermodynamic limits to microbial life at high salt concentrations.

summary
N2 fixation is an extremely O2-sensitive process. N2-fixing bacteria (diazotrophys) have therefore evolved a variety of strategies by which they maintain an active nitrogenase in the presence of atmospheric O2 and, in some cases, of O2 generated photosynthetically. In this review, the effects of O2 on nitrogenase activity and synthesis are described, as are the mechanisms by which diazotrophs limit O2damage to nitrogenase. These mechanisms are classified as behavioural strategies, physical barriers or physiological and biochemical strategies. Individual diazotrophs frequently empoly a combination of these. In addition, the particular problems faced by the O2-evolving cyanobacteria are discussed.

Reconciling the incompatible: N2 fixation And O2

Our understanding of the phylogenetic diversity, metabolic capabilities, ecological roles, and community dynamics of oil reservoir microbial communities is far from complete. The lack of appreciation of the microbiology of oil reservoirs can lead to detrimental consequences such as souring or plugging. In contrast, knowledge of the microbiology of oil reservoirs can be used to enhance productivity and recovery efficiency. It is clear that (1) nitrate and/or nitrite addition controls H2S production, (2) oxygen injection stimulates hydrocarbon metabolism and helps mobilize crude oil, (3) injection of fermentative bacteria and carbohydrates generates large amounts of acids, gases, and solvents that increases oil recovery particularly in carbonate formations, and (4) nutrient injection stimulates microbial growth preferentially in high permeability zones and improves volumetric sweep efficiency and oil recovery. Biosurfactants significantly lower the interfacial tension between oil and water and large amounts of biosurfactant can be made in situ. However, it is still uncertain whether in situ biosurfactant production can be induced on the scale needed for economic oil recovery. Commercial microbial paraffin control technologies slow the rate of decline in oil production and extend the operational life of marginal oil fields. Microbial technologies are often applied in marginal fields where the risk of implementation is low. However, more quantitative assessments of the efficacy of microbial oil recovery will be needed before microbial oil recovery gains widespread acceptance.

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Microbial processes in oil fields: culprits, problems, and opportunities.

Souring in oilfield systems is most commonly due to the action of sulfate-reducing prokaryotes, a diverse group of anaerobic microorganisms that respire sulfate and produce sulfide (the key souring agent) while oxidizing diverse electron donors. Such biological sulfide production is a detrimental, widespread phenomenon in the petroleum industry, occurring within oil reservoirs or in topside processing facilities, under low- and high-temperature conditions, and in onshore or offshore operations. Sulfate reducers can exist either indigenously in deep subsurface reservoirs or can be “inoculated” into a reservoir system during oilfield development (e.g., via drilling operations) or during the oil production phase. In the latter, souring most commonly occurs during water flooding, a secondary recovery strategy wherein water is injected to re-pressurize the reservoir and sweep the oil towards production wells to extend the production life of an oilfield. The water source and type of production operation can provide multiple components such as sulfate, labile carbon sources, and sulfate-reducing communities that influence whether oilfield souring occurs. Souring can be controlled by biocides, which can non-specifically suppress microbial populations, and by the addition of nitrate (and/or nitrite) that directly impacts the sulfate-reducing population by numerous competitive or inhibitory mechanisms. In this review, we report on the diversity of sulfate reducers associated with oil reservoirs, approaches for determining their presence and effects, the factors that control souring, and the approaches (along with the current understanding of their underlying mechanisms) that may be used to successfully mitigate souring in low-temperature and high-temperature oilfield operations.

Biological souring and mitigation in oil reservoirs.

The new mesophilic, chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium strain 11-6, could grow at a NaCl concentration in the medium of 30–230 g/l, with an optimum at 80–100 g/l. Cells were vibrios motile at the early stages of growth. Lactate, pyruvate, malate, fumarate, succinate, propionate, butyrate, crotonate, ethanol, alanine, formate, and H2/CO2 were used in sulfate reduction. Butyrate was degraded completely, without acetate accumulation. In butyrate-grown cells, a high activity of CO dehydrogenase was detected. Additional growth factors were not required. Autotrophic growth occurred, in the presence of sulfate, on H2/CO2 or formate without other electron donors. Fermentation of pyruvate and fumarate was possible in the absence of sulfate. Apart from sulfate, sulfite, thiosulfate, and elemental sulfur were able to serve as electron acceptors. The optimal growth temperature was 37°C; the optimum pH was 7.2. Desulfoviridin was not detected. Menaquinone MK-7 was present. The DNA G+C content was 55.2 mol %. Phylogenetically, the bacterium represented a separate branch within the cluster formed by representatives of the family Desulfohalobiaceae in the class Deltaproteobacteria. The bacterium was assigned to a new genus and species, Desulfovermiculus halophilus gen. nov., sp. nov. The type strain is 11-6T (= VKM B-2364), isolated from the highly mineralized formation water of an oil field.

[The new facultatively chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium Desulfovermiculus halophilus gen. nov., sp. nov., isolated from an oil field].

This study focused on the physiological, chemotaxonomic, and genotypic characteristics of two thermophilic spore-forming sulfate-reducing bacterial strains, 435T and 781, of which the former has previously been assigned to the subspecies “Desulfotomaculum nigrificans subsp. salinus”. Both strains reduced sulfate with the resulting production of H2S on media supplemented with H2 + CO2, formate, lactate, pyruvate, malate, fumarate, succinate, methanol, ethanol, propanol, butanol, butyrate, valerate, or palmitate. Lactate oxidation resulted in acetate accumulation; butyrate was oxidized completely, with acetate as an intermediate product. Growth on acetate was slow and weak. Sulfate, sulfite, thiosulfate, and elemental sulfur, but not nitrate, served as electron acceptors for growth with lactate. The bacteria performed dismutation of thiosulfate to sulfate and hydrogen sulfide. In the absence of sulfate, pyruvate but not lactate was fermented. Cytochromes of b and c types were present. The temperature and pH optima for both strains were 60–6°C and pH 7.0. Bacteria grew at 0 to 4.5–6.0% NaCl in the medium, with the optimum being at 0.5–1.0%. Phylogenetic analysis based on a comparison of incomplete 16S rRNA sequences revealed that both strains belonged to the C cluster of the genus Desulfotomaculum, exhibiting 95.5–98.3% homology with the previously described species. The level of DNA–DNA hybridization of strains 435T and 781 with each other was 97%, while that with closely related species D. kuznetsovii 17T was 51–52%. Based on the phenotypic and genotypic properties of strains 435T and 781, it is suggested that they be assigned to a new species: Desulfotomaculum salinum sp. nov., comb. nov. (type strain 435T = VKM B 1492T).

[Description of Desulfotomaculum nigrificans subsp. salinus as a new species, Desulfotomaculum salinum sp. nov].

In 1978, we described two strains (435 and 781) of thermophilic spore-forming sulfate-reducing bacteria (SRB), which on the basis of a limited number of properties were assigned to the species Desulfotomaculum nigrificans [1]. At that time, Dt. nigrificans was the only known thermophilic representative of the genus that was known to oxidize some organic substrates (not fatty acids) to acetate and ëé 2 and to grow under lithoheterotrophic conditions at the expense of ç 2 /ëé 2 and acetate [2], i.e., to realize incomplete oxidation of organic compounds, belonging thus to the first metabolic type.

Newly discovered properties of spore-forming sulfate-reducing bacteria, Desulfotomaculum strains 435 and 781

Peptic ulcer and helicobacteriosis 39

The article continues the study of the pseudepigraphic Commandment of John Chrysostom on Church Law, known in Serbian Trebniks of the 14th–15th centuries, as well as in Bulgarian and Moldavian manuscripts of the 15th–16th centuries. For the fi rst time, the characteristics of four East Slavic editions of the Commandment are given. Three of them date from the beginning of the 15th century. and are part of stable collections: collections of the “Arkhangelsk” type, the Myasnikov edition of the Kormchaja, the Kiril-Belozerosky edition of the Nomocanon of John the Faster and refl ect the process of creating new types of canonical collections. Only in the collections of the “Arkhangelsk” type is the Commandment in its entirety, including the chapter on the Bogomils. The text of the Commandment was subjected to the greatest revision in the “Barsov” edition, which is found in the composition of the “nomocanons” addressed to priests. These collections do not have a stable composition, although they contain many matching blocks. A study of the “Barsov” edition shows that the text is found not only in the tradition of monasteries, but also among collections addressed to priests.

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E. V. Belyakova

Papers

[The new facultatively chemolithoautotrophic, moderately halophilic, sulfate-reducing bacterium Desulfovermiculus halophilus gen. nov., sp. nov., isolated from an oil field].

[Description of Desulfotomaculum nigrificans subsp. salinus as a new species, Desulfotomaculum salinum sp. nov].

Newly discovered properties of spore-forming sulfate-reducing bacteria, Desulfotomaculum strains 435 and 781

Peptic ulcer and helicobacteriosis 39

The Commandment of John Chrysostom on Church Law in East Slavic Tradition (on the issue of new texts in the monastic libraries)