Acceleration of starch degradation by suppression of H-2 evolution in Chlamydomonas sp MGA161

Starch degradation was not increased under dark-anaerobiosis compared with that under dark-aerobic or light-anaerobic conditions in a green alga, Chlamydomonas sp. MGA161, though was increased in a control, C. reinhardtii. Orthophosphate (Pi) stimulated starch degradation and increased ethanol and glycerol excretion while decreasing H-2 and acetic acid formation in strain MGA161. Phosphofructokinase was little increased in cells treated with Pi. Incubation with Pi inhibited hydrogenase activity in intact cells, and was accompanied by stimulation of starch degradation. Addition of H-2 to the fermentative gas phase resulted in uptake of the H-2 and the disappearance of H-2 evolution, which in turn raised the rate of starch degradation while increasing the excretion of ethanol and glycerol and decreasing the release of acetic acid. It is suggested that the starch degradation is increased not in a state that the ATP neogenesis through proton motive force does not function in dark-anaerobiosis but in a state that the reducing equivalence is increased by H-2 uptake and repression of the release.