Improvement of hydrogen yield of lba-transgenic Chlamydomonas reinhardtii caused by increasing respiration and impairing photosynthesis

• Expression of lba in Chlamydomonas reinhardtii chloroplasts improved its H2 yield.
• Photosynthetic capacities of the transgenic alga decreased significantly.
• Respiration rates of the transgenic alga increased obviously.
• Starch contents of the transgenic alga were also improved.

The transgenic alga lba of Chlamydomonas reinhardtii yielded H2 with 50%–180% higher than the control strain. Further experiments showed that photosynthetic rates and photosynthetic reaction center II's photochemical capacities of the transgenic algae obviously decreased 33.4%–85.9% and 30.0%–51.7%, respectively, compared with those of the control. On the contrary, respiration rates of the transgenic algae significantly increased, with 40.0%–200.0% higher than those of the control. Furthermore, starch contents of the transgenic algae were also improved significantly by 79.1%–592.8% compared with the control. Therefore, the reason of H2 yield improvement of the transgenic alga lba is not only due to its decrease of photosynthetic capacity and increase of the respiration rate, but also due to the metabolic changes related to starch metabolism, photosynthesis and respiration which is possibly caused by hetero-expression of lba gene in chloroplasts of C. reinhardtii, indicating the potential of utilization of lba gene to improve hydrogen yield of micro-green algae.