Storage of solar energy as hydrogen provides aplatform towards decarbonizing our economy.One emerging strategy for the production of solar fuels is to use photocatalytic biohybrid systems that combine the high catalytic activity of non-photosynthetic microorganisms with the high light-harvesting efficiency of metal semiconductor nanoparticles.However,few such systems have been tested for H 2 production. We investigated light-driven H 2 production by three novel organisms,D esulfovibrio desulfuricans,C itrobacter freundii, and Shewanella oneidensis,s elf-photosensitized with cadmium sulfide nanoparticles,a nd compared their performance to Escherichia coli. All biohybrid systems produced H 2 from light, with D. desulfuricans-CdS demonstrating the best activity overall and outperforming the other microbial systems even in the absence of am ediator.W itht his system, H 2 was continuously produced for more than 10 days with as pecific rate of 36 mmol g dcw À1 h À1 .High apparent quantum yields of 23 %and 4% were obtained, with and without methyl viologen, respectively,exceeding values previously reported.
The genome of the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough encodes three formate dehydrogenases (FDHs), two of which are soluble periplasmic enzymes (FdhAB and FdhABC 3 ) and one that is periplasmic but membrane-associated (FdhM). FdhAB and FdhABC 3 were recently shown to be the main enzymes present during growth with lactate, formate or hydrogen. To address the role of these two enzymes, DfdhAB and DfdhABC 3 , mutants were generated and studied. Different phenotypes were observed in the presence of either molybdenum or tungsten, since both enzymes were important for growth on formate in the presence of Mo, whereas in the presence of W only FdhAB played a role. Both DfdhAB and DfdhABC 3 mutants displayed defects in growth with lactate and sulfate providing the first direct evidence for the involvement of formate cycling under these conditions. In support of this mechanism, incubation of concentrated cell suspensions of the mutant strains with lactate and limiting sulfate also gave elevated formate concentrations, as compared to the wild-type strain. In contrast, both mutants grew similarly to the wild-type with H 2 and sulfate. In the absence of sulfate, the wild-type D. vulgaris cells produced formate when supplied with H 2 and CO 2 , which resulted from CO 2 reduction by the periplasmic FDHs. The conversion of H 2 and CO 2 to formate allows the reversible storage of reducing power in a much more soluble molecule. Furthermore, we propose this may be an expression of the ability of some sulfate-reducing bacteria to grow by hydrogen oxidation, in syntrophy with organisms that consume formate, but are less efficient in H 2 utilization.
Biological treatment with dissimilatory sulphate-reducing bacteria has been considered the most promising alternative for decontamination of sulphate rich effluents. These wastewaters are usually deficient in electron donors and require their external addition to achieve complete sulphate reduction. The aim of the present study was to investigate the possibility of using food industry wastes (a waste from the wine industry and cheese whey) as carbon sources for dissimilatory sulphate-reducing bacteria. The results show that these wastes can be efficiently used by these bacteria provided that calcite tailing is present as a neutralizing and buffer material. A 95 and 50 % sulphate reduction was achieved within 20 days of experiment by a consortium of dissimilatory sulphate-reducing bacteria grown on media containing waste from the wine industry or cheese whey respectively. Identification of the dissimilatory sulphate-reducing bacteria community using the dsr gene revealed the presence of the species Desulfovibrio fructosovorans, Desulfovibrio aminophilus and Desulfovibrio desulfuricans. The findings of the present study emphasise the potential of using wastes from the wine industry as carbon source for dissimilatory sulphate-reducing bacteria, combined with calcite tailing, in the development of cost effective and environmentally friendly bioremediation processes.
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