Long-term H 2 photoproduction from starch by co-culture of Clostridium butyricum and Rhodobacter sphaeroides in a repeated batch process.

OBJECTIVES: To prove the possibility of efficient starch photofermentation in co-culture of heterotrophic and phototrophic bacteria over prolonged period.

RESULTS: Repeated batch photofermentation of starch was demonstrated in co-culture Clostridium butyricum and Rhodobacter sphaeroides under microaerobic conditions. It continued 15 months without addition of new inoculum or pH regulation when using 4-5 g starch l-1 and 0.04 g yeast extract l-1 . The complete degradation of starch without volatile fatty acids accumulation was shown in this co-culture. The average H2 yield of 5.2 mol/mol glucose was much higher than that in Clostridium monoculture. The species composition of co-culture was studied by q-PCR assay. The concentration of Clostridium cells in prolonged co-culture was lower than in monoculture and even in a single batch co-culture. This means that Clostridia growth was significantly limited whereas starch hydrolysis still took place.

CONCLUSION: The prolonged repeated batch photofermentation of starch by co-culture C. butyricum and R. sphaeroides provided efficient H2 production without accumulation of organic acids under conditions of Clostridia limitation.