title: Effect of algal extract on H2 production by a photosynthetic bacterium Rhodobium marinum A-501: analysis of stimulating effect using a kinetic model.
abstract: We have established a system for hydrogen (H2) production from algal starch via lactic acid using a mixed culture of a lactic acid bacterium, Lactobacillus amylovorus, and a photosynthetic bacterium, Rhodobium marinum A-501. We found that the H2 production from lactate was stimulated in the presence of algal extract, which was obtained from algal biomass homogenate used as a substrate in the system by removing settleable solids including starch. To analyze the stimulating effect of algal extract on H2 production, we developed a kinetic model for H2 production by R. marinum A-501. The model revealed that approximately 20% of lactate was consumed for cell mass production, and the remaining portion was a source of reducing power to drive hydrogen production or other cellular processes. In the presence of algal extract, the model indicated that the conversion efficiency from lactate to the reducing power increased from 0.56 to 0.80 and nitrogenase activity increased up to twofold, resulting in the increase in yield of hydrogen from lactate from 29% to 48%. These results suggest that algal extract can attenuate the limitation process in lactate catabolism by which the supplementation of reducing power to drive H2 production was suppressed.
authors.affiliation: Environmental Bioengineering Laboratory, Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka 565-0871, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Kawaguchi
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Nagase
authors.forename: Kyoko
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Shiho
authors.initials: S
authors.lastname: Kimata
authors.forename: Mikio
authors.initials: M
authors.lastname: Doi
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Hirata
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Miyamoto