Integration of purple non-sulfur bacteria into the starch-hydrolyzing consortium

Purple non-sulfur bacteria Rhodobacter sphaeroides N7 was integrated into the heterotrophic starch-hydrolyzing consortium containing Clostridium butyricum as the main component. The resulting light-dependent consortium with Bchl ∼9 μg/ml was maintained during 12 months of regular transfers. The protein content in this consortium was four-fold higher compared to the heterotrophic consortium, suggesting that purple bacteria became its important component. Under illumination, the starch hydrolysis by the light-dependent consortium (as opposed to heterotrophic consortium) resulted in the absence of VFAs, hydrogen production being quite similar and residual hexose higher. Fermentation of glucose (unlike to starch) by the light-dependent consortium or Rb. sphaeroides alone resulted in ∼3 fold increase of hydrogen production compared to the heterotrophic consortium. Apparently, hydrolysis of starch to hexose was the bottleneck in H₂ photoproduction by the light-dependent consortium. Availability of residual hexose after photofermentation of starch/glucose by the light-dependent consortium or Rb. sphaeroides is discussed.