A truncated antenna mutant of Chlamydomonas reinhardtii can produce more hydrogen than the parental strain

Photoproduction of H2 gas was examined in the Chlamydomonas reinhardtii tla1 strain, CC-4169, containing a truncated light-harvesting antenna, along with its parental CC-425 strain. Although enhanced photosynthetic performance of truncated antenna algae has been demonstrated previously (Polle et al. Planta 2003; 217:49–59), improved H2 photoproduction has yet to be reported. Preliminary experiments showed that sulfur-deprived, suspension cultures of the tla1 mutant could not establish anaerobiosis in a photobioreactor, and thus, could not photoproduce H2 gas under conditions typical for the sulfur-deprived wild-type cells (Kosourov et al. Biotech Bioeng 2002; 78:731–40). However, they did produce H2 gas when deprived of sulfur and phosphorus after immobilization within thin (∼300 μm) alginate films. These films were monitored for long-term H2 photoproduction activity under light intensities ranging from 19 to 350 μE m−2 s−1 PAR. Both the tla1 mutant and the CC-425 parental strain produced H2 gas for over 250 h under all light conditions tested. Relative to the parental strain, the CC-4169 mutant had lower maximum specific rates of H2 production at low and medium light intensities (19 and 184 μE m−2 s−1), but it exhibited a 4-times higher maximum specific rate at 285 μE m−2 s−1 and an 8.5-times higher rate at 350 μE m−2 s−1 when immobilized at approximately the same cell density as the parental strain. As a result, the CC-4169 strain accumulated almost 4-times more H2 than CC-425 at 285 μE m−2 s−1 and over 6-times more at 350 μE m−2 s−1 during 250-h experiments. These results are the first demonstration that truncating light-harvesting antennae in algal cells can increase the efficiency of H2 photoproduction in mass culture at high light intensity.