title: Sustained hydrogen photoproduction by Chlamydomonas reinhardtii: Effects of culture parameters.
abstract: The green alga, Chlamydomonas reinhardtii, is capable of sustained H(2) photoproduction when grown under sulfur-deprived conditions. This phenomenon is a result of the partial deactivation of photosynthetic O(2)-evolution activity in response to sulfur deprivation. At these reduced rates of water-oxidation, oxidative respiration under continuous illumination can establish an anaerobic environment in the culture. After 10-15 hours of anaerobiosis, sulfur-deprived algal cells induce a reversible hydrogenase and start to evolve H(2) gas in the light. Using a computer-monitored photobioreactor system, we investigated the behavior of sulfur-deprived algae and found that: (1) the cultures transition through five consecutive phases: an aerobic phase, an O(2)-consumption phase, an anaerobic phase, a H(2)-production phase and a termination phase; (2) synchronization of cell division during pre-growth with 14:10 h light:dark cycles leads to earlier establishment of anaerobiosis in the cultures and to earlier onset of the H(2)-production phase; (3) re-addition of small quantities of sulfate (12.5-50 microM MgSO(4), final concentration) to either synchronized or unsynchronized cell suspensions results in an initial increase in culture density, a higher initial specific rate of H(2) production, an increase in the length of the H(2)-production phase, and an increase in the total amount of H(2) produced; and (4) increases in the culture optical density in the presence of 50 microM sulfate result in a decrease in the initial specific rates of H(2) production and in an earlier start of the H(2)-production phase with unsynchronized cells. We suggest that the effects of sulfur re-addition on H(2) production, up to an optimal concentration, are due to an increase in the residual water-oxidation activity of the algal cells. We also demonstrate that, in principle, cells synchronized by growth under light:dark cycles can be used in an outdoor H(2)-production system without loss of efficiency compared to cultures that up until now have been pre-grown under continuous light conditions.
authors: Basic Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA.
authors: Sergey
authors: S
authors: Kosourov
authors: Anatoly
authors: A
authors: Tsygankov
authors: Michael
authors: M
authors: Seibert
authors: Maria L
authors: ML
authors: Ghirardi
mesh_terms: D000332:Aerobiosis / Q000502:physiology; D000693:Anaerobiosis / Q000502:physiology; D000818:Animals; D019149:Bioreactors; D002452:Cell Count; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D003470:Culture Media; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000378:metabolism*; D008278:Magnesium Sulfate / Q000378:metabolism* / Q000494:pharmacology; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D010788:Photosynthesis; D012680:Sensitivity and Specificity; D013696:Temperature
chemical_list: D003470:Culture Media; D008278:Magnesium Sulfate; D006859:Hydrogen; D006864:Hydrogenase