Methanol-induced stimulation of growth, intracellular amino acids, and protein content in Chlamydomonas reinhardtii

Methanol in low concentrations can stimulate the mixotrophic growth of some microscopic algae. The aim of the present work was to investigate the effect of methanol on the growth, photosynthesis, and respiration rate as well as free amino acid and soluble protein content in the cells of unicellular green alga Chlamydomonas reinhardtii. It was shown that 30-100 mM methanol induced an increase in C. reinhardtii biomass production compared to controls without the solvent. The packed cell volume was increased maximally by 35 % after growing for 6 days in the presence of 50 mM methanol. The effect was light-dependent, although the rate of photosynthesis changed insignificantly while the rate of respiration increased. The intracellular content of reduced nicotinamide coenzyme NAD(P)H also increased after methanol addition in the light. The intracellular content of free amino acids increased by 31% as a result of 50 mMmethanol addition, and their composition changed: glutamic acid, glutamine, alanine, serine, and tyrosine increased and methionine content decreased. The content of soluble protein also increased by 30 %, eliminating the possibility of proteolysis. Thus, methanol has a positive effect on nitrogen assimilation as indicated by the increase in the content of soluble proteins and free amino acids. This effect may be connected with methanol-induced stimulation of respiration and the lightdependent increase in NAD(P) H content. The results suggest that methanol not only is a carbon source for C. reinhardtii cells but also can take part in energy metabolism.