Different types of H2 photoproduction by starch-utilizing co-cultures of Clostridium butyricum and Rhodobacter sphaeroides

• Co-culture Clostridium and Rhodobacter displays different H2 photoproduction types.
• H2 photoproduction types in co-culture differs in yields and temporal parameters.
• Dependence of H2 photoproduction by co-culture on numerous factors is demonstrated.
• Ways to increase H2 photoproduction by co-culture depend on the process type.

Co-culture of Clostridium butyricum and Rhodobacter sphaeroides displayed different types of H2 photoproduction from starch: quick low-yield (2.6 mol/mol glucose), prolonged high-yield (6.1 mol/mol glucose) and delayed low-yield (4.2 mol/mol glucose). It depended primarily on the ratio of two species and, besides, some other factors. The first type H2 photoproduction was similar to that in Clostridium, observed at high clostridia/purple bacteria ratio and promoted by low light intensity, temperature above and below optimum, reduced conditions, low initial pH or buffer concentration, high concentration of yeast extract (320 mg/L). The second type, high yield H2 production, was favored by low clostridia/purple bacteria ratio, high light intensity, and high concentration of yeast extract (320 mg/L). The third type, delayed H2 photoproduction, was observed at the lowest clostridia/purple bacteria ratio and was promoted by low concentration of yeast extract (25 mg/L). Thus, a well-known crucial effect of a species ratio on H2 photoproduction was in turn controlled by other factors, especially yeast extract concentration.