The effect of sulfur re-addition on H(2) photoproduction by sulfur-deprived green algae.
Sulfur deprivation of algal cultures selectively and partially inactivates photosystem II (PSII)-catalyzed O(2) evolution, induces anaerobiosis and hydrogenase expression, and results in sustained H(2) photoproduction for several days. We show that re-addition of limiting amounts of sulfate (1-10 microM final concentration) to the cultures during the H(2)-production phase temporarily reactivates PSII photochemical and O(2)-evolution activity and re-establishes higher rates of electron transport through the photosynthetic electron transport chain. The reactivation of PSII occurs by de novo D1 protein synthesis, but does not result in the re-establishment of aerobic conditions in the reactor, detectable by dissolved-O(2) sensors. However, concomitant H(2) photoproduction is inhibited, possibly due to excessive intra-cellular levels of photosynthetically-evolved O(2). The partial recovery of electron transport rates correlates with the re-oxidation of the plastoquinone (PQ) pool, as observed by pulse-amplitude modulated (PAM) and fluorescence-induction measurements. These results show that the presence of a more oxidized PQ pool releases some of the down-regulation of electron transport caused by the anaerobic conditions.
Kosourov
Sergey
S
National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, USA.
Makarova
Valeriya
V
Fedorov
Alexander S
AS
Tsygankov
Anatoly
A
Seibert
Michael
M
Ghirardi
Maria L
ML
D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism*; D004579:Electron Transport / Q000187:drug effects; D005453:Fluorescence; D006859:Hydrogen / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology; D010971:Plastoquinone / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism / Q000494:pharmacology*; D013455:Sulfur / Q000172:deficiency* / Q000378:metabolism; D013997:Time Factors
D013431:Sulfates; D013455:Sulfur; D006859:Hydrogen; D010971:Plastoquinone; D010100:Oxygen