Photoproduction of hydrogen by sulfur-deprived C. reinhardtii mutants with impaired Photosystem II photochemical activity

Abstract

Photoproduction of H2 was examined in a series of sulfur-deprived Chlamydomonas reinhardtii D1-R323 mutants with progressively impaired PSII photochemical activity. In the R323H, R323D, and R323E D1 mutants, replacement of arginine affects photosystem II (PSII) function, as demonstrated by progressive decreases in O2-evolving activity and loss of PSII photochemical activity. Significant changes in PSII activity were found when the arginine residue was replaced by negatively charged amino acid residues (R323D and R323E). However, the R323H (positively charged or neutral, depending on the ambient pH) mutant had minimal changes in PSII activity. The R323H, R323D, and R323E mutants and the pseudo-wild-type (pWt) with restored PSII function were used to study the effects of sulfur deprivation on H2-production activity. All of these mutants exhibited significant changes in the normal parameters associated with the H2-photoproduction process, such as a shorter aerobic phase, lower accumulation of starch, a prolonged anaerobic phase observed before the onset of H2-production, a shorter duration of H2-production, lower H2 yields compared to the pWt control, and slightly higher production of dark fermentation products such as acetate and formate. The more compromised the PSII photochemical activity, the more dramatic was the effect of sulfur deprivation on the H2-production process, which depends both on the presence of residual PSII activity and the amount of stored starch.

Increased photosystem II stability promotes H2production in sulfur-deprivedChlamydomonas reinhardtii

“…This observation is important because it is opens up a way to improve the H 2 production in green algae, which is based on enhanced respiratory reactions, similar to Stm6 and some other mutant systems (23,27,39). The search for existing mutations or engineering of new ones, which can create earlier and extended anaerobic conditions, will potentially overcome two major problems.…”

Implementation of photobiological H2 production: the O2 sensitivity of hydrogenases

“…Sulfate permease mutants had a phenotype similar to that of sulfur-deprived wild-type algae and produced H 2 at similar levels (Chen et al 2005). A different approach focused on the feasibility of using D1 mutants with reported lower O 2 evolution capability as H 2 -producers in closed photobioreactors (Makarova et al 2007). Unfortunately, the specific mutants used in this study were unable to over-accumulate starch, a sine-qua-non for efficient H 2 photoproduction during anaerobiosis.…”

Relevance of nutrient media composition for hydrogen production in Chlamydomonas

“…This has been used to propose that the low residual PSII activity is the predominant H 2 production pathway during S deprivation. It has been estimated that about 90-60 % of H 2 production is PSII-dependent Fouchard et al 2005;Hemschemeier et al 2008;Antal et al 2009Antal et al , 2011, and that the PSII centers that remain active during the anaerobiosis phase (Makarova et al 2007;Antal et al 2011;Volgusheva et al 2013) contribute to sustain the H 2 production observed during S deficiency.…”