Biohydrogen production from engineered microalgae Chlamydomonas reinhardtii

Abstract

The green microalgae Chlamydomonas reinhardtti is well-known specie in the terms of <TEX>$H_2$</TEX> production by photo fermentation and has been studying for a long time. Although the <TEX>$H_2$</TEX> production yield is promising; there are some bottlenecks to enhance the yield and efficiency to focus on a well-designed, sustainable production and also scaling up for further studies. D1 protein of photosystem II (PSII) plays an important role in photosystem damage repair and related to <TEX>$H_2$</TEX> production. Because Chlamydomonas is the model algae and the genetic basis is well-studied; metabolic engineering tools are intended to use for enhanced production. Mutations are focused on D1 protein which aims long-lasting hydrogen production by blocking the PSII repair system thus <TEX>$O_2$</TEX> sensitive hydrogenases catalysis hydrogen production for a longer period of time under anaerobic and sulfur deprived conditions. Chlamydomonas CC124 as control strain and D1 mutant strains(D240, D239-40 and D240-41)are cultured photomixotrophically at <TEX>$80{\mu}mol\;photons\;m^{-2}s^{-1}$</TEX>, by two sides. Cells are grown in TAP medium as aerobic stage for culture growth; in logarithmic phase cells are transferred from aerobic to an anaerobic and sulfur deprived TAP- S medium and 12 mg/L initial chlorophyll content for <TEX>$H_2$</TEX> production which is monitored by the water columns and later detected by Gas Chromatography. Total produced hydrogen was <TEX>$82{\pm}10$</TEX>, <TEX>$180{\pm}20$</TEX>, <TEX>$196{\pm}20$</TEX>, <TEX>$290{\pm}30mL$</TEX> for CC124, D240, D239-40, D240-41, respectively. <TEX>$H_2$</TEX> production rates for mutant strains was <TEX>$1.3{\pm}0.5mL/L.h$</TEX> meanwhile CC124 showed 2-3 fold lower rate as <TEX>$0.57{\pm}0.2mL/L.h$</TEX>. Hydrogen production period was <TEX>$5{\pm}2days$</TEX> for CC124 and mutants showed a longer production time for <TEX>$9{\pm}2days$</TEX>. It is seen from the results that <TEX>$H_2$</TEX> productions for mutant strains have a significant effect in terms of productivity, yield and production time.