Evidences of oxidative stress during hydrogen photoproduction in sulfur-deprived cultures of Chlamydomonas reinhardtii

Biological hydrogen production is being evaluated for use as fuel, since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific energy content. The microalga Chlamydomonas reinhardtii when grown under sulfur-deprived conditions, switches themetabolismtoward the production of hydrogen.A better understandings of physiological and biochemical changes occurringduring eachphases of the process, represents a prerequisite to enhance the hydrogen output. The aimof this workwas to studywhether the activation of enzymes of the antioxidant defense system, such as catalase (CAT), ascorbate peroxidase (APOX) and guaiacol peroxidase (GPOX), takes place during the entire process of hydrogen production by C. reinhardtii CC 124. Kinase activities present in the crude protein extract and themitotic specific ones associated with CKS1 protein were assayed to determine howthe conditions leading tohydrogenproductionaffectedthe activities ofmitotic andgrowth associated kinases.We present evidences that oxidative stress enzymes are active during the entire hydrogen production process, besides their activities are higher in the anoxic phase. Stress condition during hydrogen photoproduction provoked at least partial cell cycle arrest leading to block of mitosis and cell division. These findings are in line with the known downregulation or block of cell cycle related processes in stressed or starved cells.