Sulfate reduction and possible aerobic metabolism of the sulfate-reducing bacterium Desulfovibrio oxyclinae in a chemostat coculture with Marinobacter sp. strain MB under exposure to increasing oxygen concentrations

A chemostat coculture of the sulfate-reducing bacterium Desulfovibrio oxyclinae together with a facultative aerobe heterotroph tentatively identified as Marinobacter sp. strain MB was grown under anaerobic conditions and then exposed to a stepwise-increasing oxygen influx (0 to 20% O2 in the incoming gas phase). The coculture consumed oxygen efficiently, and no residual oxygen was detected with an oxygen supply of up to 5%. Sulfate reduction persisted at all levels of oxygen input, even at the maximal level, when residual oxygen in the growth vessel was 87 μM. The portion of D. oxyclinae cells in the coculture decreased gradually from 92% under anaerobic conditions to 27% under aeration. Both absolute cell numbers and viable cell counts of the organism were the same as or even higher than those observed in the absence of oxygen input. The patterns of consumption of electron donors and acceptors suggest that aerobic incomplete oxidation of lactate to acetate is performed by D. oxyclinae under high oxygen input. Both organisms were isolated from the same oxic zone of a cyanobacterial mat where they have to adapt to daily shifts from oxic to anoxic conditions. This type of syntrophic association may occur in natural habitats, enabling sulfate-reducing bacteria to cope with periodic exposure to oxygen

Molecular identification of bacteria from a coculture by denaturing gradient gel electrophoresis of 16S ribosomal DNA fragments as a tool for isolation in pure cultures

Molecular information about the bacterial composition of a coculture capable of sulfate reduction after exposure to oxic and microoxic conditions was used to identify and subsequently to isolate the components of the mixture in pure culture. PCR amplification of 16S ribosomal DNA fragments from the coculture, analyzed by denaturing gradient gel electrophoresis, resulted in two distinct 16S ribosomal DNA bands, indicating two different bacterial components. Sequencing showed that the bands were derived from a Desulfovibrio strain and an Arcobacter strain. Since the phylogenetic positions of bacteria are often consistent with their physiological properties and culture requirements, molecular identification of the two components of this coculture allowed the design of specific culture conditions to separate and isolate both strains in pure culture. This approach facilitates the combined molecular and physiological analysis of mixed cultures and microbial communities

Biodesalination: A Case Study for Applications of Photosynthetic Bacteria in Water Treatment

Shortage of freshwater is a serious problem in many regions worldwide, and is expected to become even more urgent over the next decades as a result of increased demand for food production and adverse effects of climate change. Vast water resources in the oceans can only be tapped into if sustainable, energy-efficient technologies for desalination are developed. Energization of desalination by sunlight through photosynthetic organisms offers a potential opportunity to exploit biological processes for this purpose. Cyanobacterial cultures in particular can generate a large biomass in brackish and seawater, thereby forming a low-salt reservoir within the saline water. The latter could be used as an ion exchanger through manipulation of transport proteins in the cell membrane. In this article, we use the example of biodesalination as a vehicle to review the availability of tools and methods for the exploitation of cyanobacteria in water biotechnology. Issues discussed relate to strain selection, environmental factors, genetic manipulation, ion transport, cell-water separation, process design, safety, and public acceptance

Molecular identification of bacteria from a coculture by denaturing gradient gel electrophoresis of 16S ribosomal DNA fragments as a tool for isolation in pure cultures.

Molecular information about the bacterial composition of a coculture capable of sulfate reduction after exposure to oxic and microoxic conditions was used to identify and subsequently to isolate the components of the mixture in pure culture. PCR amplification of 16S ribosomal DNA fragments from the coculture, analyzed by denaturing gradient gel electrophoresis, resulted in two distinct 16S ribosomal DNA bands, indicating two different bacterial components. Sequencing showed that the bands were derived from a Desulfovibrio strain and an Arcobacter strain. Since the phylogenetic positions of bacteria are often consistent with their physiological properties and culture requirements, molecular identification of the two components of this coculture allowed the design of specific culture conditions to separate and isolate both strains in pure culture. This approach facilitates the combined molecular and physiological analysis of mixed cultures and microbial communities

A sulfate-reducing bacterium from the oxic layer of a microbial mat from Solar Lake (Sinai), Desulfovibrio oxyclinae sp. nov.

In an investigation on the oxygen tolerance of sulfate-reducing bacteria, a strain was isolated from a 10(7)-fold dilution of the upper 3-mm layer of a hypersaline cyanobacterial mat (transferred from Solar Lake, Sinai). The isolate, designated P1B, appeared to be well-adapted to the varying concentrations of oxygen and sulfide that occur in this environment. In the presence of oxygen strain P1B respired aerobically with the highest rates [260 nmol O-2 min(-1) (mg protein)(-1)] found so far among marine sulfate-reducing bacteria. Besides H-2 and lactate, even sulfide or sulfite could be oxidized with oxygen. The sulfur compounds were completely oxidized to sulfate. Under anoxic conditions, it grew with sulfate, sulfite, or thiosulfate as the electron acceptor using H-2, lactate, pyruvate, ethanol, propanol, or butanol as the electron donor. Furthermore, in the absence of electron donors the isolate grew by disproportionation of sulfite or thiosulfate to sulfate and sulfide. The highest respiration rates with oxygen were obtained with H-2 at low oxygen concentrations. Aerobic growth of homogeneous suspensions was not obtained. Additions of 1% oxygen to the gas phase of a continuous culture resulted in the formation of cell clumps wherein the cells remained viable for at least 200 h. It is concluded that strain P1B is oxygen-tolerant but does not carry out sulfate reduction in the presence of oxygen under the conditions tested. Analysis of the 16S rDNA sequence indicated that strain P1B belongs to the genus Desulfovibrio, with Desulfovibrio halophilus as its closest relative. Based on physiological properties strain P1B could not be assigned to this species. Therefore, a new species, Desulfovibrio oxyclinae, is proposed