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

Photoproduction of H(2) 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 etal. Planta 2003; 217:49-59), improved H(2) 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 H(2) gas under conditions typical for the sulfur-deprived wild-type cells (Kosourov et al. Biotech Bioeng 2002; 78:731-40). However, they did produce H(2) gas when deprived of sulfur and phosphorus after immobilization within thin (similar to 300 mu m) alginate films. These films were monitored for long-term H(2) photoproduction activity under light intensities ranging from 19 to 350 mu E m(-2) s(-1) PAR. Both the tla1 mutant and the CC-425 parental strain produced H(2) 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 H(2) production at low and medium light intensities (19 and 184 mu E m(-2) s(-1)), but it exhibited a 4-times higher maximum specific rate at 285 mu E m(-2) s(-1) and an 8.5-times higher rate at 350 mu E 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 H(2) than CC-425 at 285 mu E M(-2) s(-1) and over 6-times more at 350 mu E 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. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved

Sustained hydrogen photoproduction by phosphorus-deprived Chlamydomonas reinhardtii cultures

This study demonstrates that, besides sulfur deprivation, sustained H-2 photoproduction in Chlamydomonas reinhardtii cultures can be generated by incubating algae under phosphorus-deprived (-P) conditions. However, phosphorus deficiency in algal cells could not be obtained by resuspension of algae in -P medium, evidently due to a significant reserve of phosphorus in cells. In this study, phosphorus deficiency was accomplished by inoculating the washed algae into the -P medium at low initial cell densities (below 2 mg Chl l(-1)). After the initial growth period, where cells utilize intracellular phosphorus, algae established anaerobic environment followed by the period of H-2 photoproduction. The maximum H-2 output (similar to 70 ml l(-1)) was obtained in cultures with the initial Chl content similar to 1 mg l(-1). Cultures with Chl above 2 mg l(-1) did not produce H-2 gas. The physiological response of algal cultures to phosphorus deprivation demonstrated significant similarities with the response of algae to sulfur depletion. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Hydrogen production by sulfur-deprived Chlamydomonas reinhardtii under photoautotrophic conditions

Thus far, all experiments leading to H-2 production by sulfur-deprived cultures of microalga have been done with photoheterotrophic cultures in the presence of acetate, which increases the cost of the H-2 produced. This study demonstrates that sustained H-2 photoproduction by a sulfur-deprived green alga, Chlamydomonas reinhardtii, is possible under strictly photoautotrophic conditions in the absence of acetate or any other organic substrate in the medium. To accomplish this, we used cultures pre-grown with 2% CO2 under low light conditions (25 mu E m(-2) s(-1)) and also supplemented with CO2 during S-deprivation, along with a special light regime. Maximum H-2 production (56.4 +/- 16.7 ml l(-1) culture, equal to 56.4 x 10(-3) m(3) m(-3) culture) was observed with photoautotrophic cultures: (a) supplied with carbon dioxide for the first 24 h of sulfur deprivation, (b) exposed during the O-2-producing stage to high light (110 - 120 mu E m(-2) s(-1)), and (c) then exposed to low light (20 - 25 mu E m(-2) s(-1)) during the O-2-consumption and H-2-production stages. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved

Prolongation of H2 photoproduction by immobilized, sulfur-limited Chlamydomonas reinhardtii cultures

Two approaches to prolong the duration of hydrogen production by immobilized, sulfur-limited Chlamydomonas reinhardtii cells are examined. The results demonstrate that continuous H(2) photoproduction can occur for at least 90 days under constant flow of TAP medium containing micromolar sulfate concentrations. Furthermore, it is also possible to prolong the duration of H(2) production by cycling immobilized cells between minus and plus sulfate conditions. (C) 2008 Elsevier B.V. All rights reserved

Maximizing the hydrogen photoproduction yields in Chlamydomonas reinhardtii cultures: The effect of the H-2 partial pressure

Photoproduction of H-2 gas has been examined in sulfur/phosphorus-deprived Chalmydomonas reinhardtii cultures, placed in photobioreactors (PhBRs) with different gas phase to liquid phase ratios (V-g.p/V-l.p). The results demonstrate that an increase in the ratio stimulates H-2 photoproduction activity in both algal suspension cultures and in algae entrapped in thin alginate films. In suspension cultures, a 4x increase (from similar to 0.5 to similar to 2) in V-g.p/V-l.p in a 2x increase (from 10.8 to 23.1 mmol l(-1) or 264-565 ml l(-1)) in the total yield of H-2 gas. Remarkably, 565 ml of H-2 gas per liter of the suspension culture is the highest yield ever reported for a wild-type strain in a time period of less than 190 h. In immobilized algae, where diffusion of H-2 from the medium to the PhBR gas phase is not affected by mixing, the maximum rate and yield of H-2 photoproduction occur in PhBRs with V-g.p/V-l.p above 7 or in a PhBR with smaller headspace, if the H-2 is effectively removed from the medium by continuous flushing of the headspace with argon. These experiments in combination with studies of the direct inhibitory effect of high H-2 concentrations in the PhBR headspace on H-2 photoproduction activity in algal cultures clearly show that H-2 photoproduction in algae depends significantly on the partial pressure of H-2 (not O-2 as previously thought) in the PhBR gas phase. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved