Use of Levulinic Acid byRhodopseudomonassp. No. 7 for Phototrophic Growth and Enhanced Hydrogen Evolution

A purple nonsulfur bacterium, Rhodopseudomonas sp. No.7, grew well in a salt medium containing levulinic acid (LA) as a source of carbon and an electron donor. When strain No.7 was incubated in a medium containing glutamate as a nitrogen source, it continued to evolve hydrogen from 20 mM LA for about 200 h with a yield of hydrogen of more than 75%. The consumption of LA by resting cells was strongly dependent on light. The level of 5-aminolevulinic acid dehydratase (EC 4.2.1.24) in cells grown in the LA-medium increased about 2 to 5 times over that of cells grown in LA-free media. However, about 50% inhibition of the enzyme activity in cell-free extracts prepared from these cells was observed in the presence of 5 mM LA regardless of growth conditions. Rhodopseudomonas palustris and Rhodopseudomonas acidophila could use LA for growth like strain No.7, but Rhodopseudomonas blastica, Rhodospirillum rubrum, Rhodobacter sphaeroides, Rubrivivax gelatinosus, and Rhodocyclus tenuis could not.