effect of sulfur re-addition on H₂ photoproduction by sulfur-deprived green algae

• Published in: Photosynthesis research Vol. 85; no. 3; pp. 295 - 305
• Main Authors: Kosourov, S, Makarova, V, Fedorov, A.S, Tsygankov, A, Seibert, M, Ghirardi, M.L
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Nature B.V 01.09.2005
• Subjects: Algae; algae and seaweeds; Chlamydomonas reinhardtii; chlorophyll; D1 protein; electron transport chain; Enzymes; Fluorescence; hydrogen; Photosynthesis; photosystem II; plastoquinone; Sulfur
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-005-5105-0

Sulfur deprivation of algal cultures selectively and partially inactivates photosystem II (PSII)-catalyzed O^sub 2^ evolution, induces anaerobiosis and hydrogenase expression, and results in sustained H^sub 2^ photoproduction for several days. We show that re-addition of limiting amounts of sulfate (1-10 μM final concentration) to the cultures during the H^sub 2^-production phase temporarily reactivates PSII photochemical and O^sub 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^sub 2^ sensors. However, concomitant H^sub 2^ photoproduction is inhibited, possibly due to excessive intra-cellular levels of photosynthetically-evolved O^sub 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.[PUBLICATION ABSTRACT]