Hydrogen production by a mixed photoheterotrophic culture: Correlation between gene expression analysis and physiological behavior

Photoheterotrophic bacteria use mechanisms such as H2 production, carbon dioxide fixation, and the polyhydroxybutyrate (PHB) synthesis to maintain redox balance. Therefore, these aspects must be studied from a metabolic and genomic perspective to optimize the H2 production. In this study, six genes (nifH, hupS, hoxA, nuoF, phbC and depA) in a photoheterotrophic mixed culture, whose predominant population was Rhodopseudomonas palustris, were studied. The transcriptional activity of the genes was determined by quantitative-PCR under two different conditions: H2 production and PHB accumulation. Differences in the genes expression level were found compared to those reported in pure strains. The high expression of the nuoF gene during H2 production, suggest that this is a key enzyme to regulate the reducing power, and it was correlated with a high H2 yield (3.4 mol H2/mol acetate). This last aspect is also explained by the low expression of the uptake hydrogenase gene, hupS.