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 H ₂ 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 H ₂ photoproduction in mass culture at high light intensity.