Optimizing photoheterotrophic H2 production by Rhodobacter capsulatus upon interposon mutagenesis in the hupL gene

In Rhodobacter capsulatus, the hupL gene encoding the large subunit of the uptake-hydrogenase (Hup) enzyme complex was mutated by insertion of an interposon. The mutant neither synthesized an active hydrogenase nor grew photoautotrophically. Under conditions of nitrogen (N) limitation, photoheterotrophic cultures of the wild type and the mutant evolved H2 by activity of the nitrogenase enzyme complex. When grown with glutamate as an N source and either D,L-malate or L-lactate as carbon sources, the efficiency of H2 production by the HupL mutant was higher than 90%, whereas wild-type cultures exhibited efficiencies of 54% (with D,L-malate) and 64% (with L-lactate), respectively. With NH4+ as the N source, efficiencies of H2 production were 70% (mutant) and 52% (wild type).