A Rhodopseudomonas palustris nifA* mutant produces H2 from NH4+-containing vegetable wastes

Research on photobiological H2 production processes is pointing towards the use of low cost substrates as sources of reduced carbon for H2 generation.Those substrates (either wastewaters or effluents derived from other fermentation processes) are often rich not only in carbon, but also in fixed nitrogen. NH4+ is an inhibitor of nitrogenase-mediated H2 production in purple non sulfur bacteria.A Rhodopseudomonas palustris   mutant strain (NifA*), which constitutively expresses nitrogenase genes, was utilized in order to test the use of NH4+ containing fermentation products for photobiological production of H2. The strain was grown on both synthetic and waste-derived NH4+ containing media.The nifA* mutant produced H2 in the presence of high concentrations of NH4+, both in a synthetic medium and in a real vegetable waste-derived medium resulting in higher H2 levels than the wild-type strain. Thus, this study demonstrates that the NifA* strain is well suited to overcome the effects of inhibitory naturally occurring NH4+ as it converts agricultural waste into biofuel.

► Rp. palustris nif  A* mutant is insensitive to NH4+ in a range between 2.5 and 10 mM. ► The waste derived medium is suitable for H2 production by both the strains tested. ► The nifA* mutation made cells produce H2 on a waste derived medium without dilution. ► Dilution of the medium sped up the process and increased photosynthetic efficiency.