Environmental manipulation of growth and energy carrier release from freshwater and marine Chlamydomonas species

Abstract

While many microbial species produce glycerol as an internal osmoregulant, only some species release glycerol into the external medium. The present study compared the synergistic effects of light intensity and salinity on rates of glycerol release and growth in two marine species of Chlamydomonas (C. euryale and C. hedleyi) versus a freshwater species (C. reinhardtii). High light intensity stimulated both glycerol release and algal growth in all species, presumably by stimulating photosynthesis and thereby the production of the energy carrier glycerol. The freshwater species exhibited a lower salinity threshold than the marine species for both glycerol release and growth retardation. These findings suggest (i) that there is competition between the production and release of glycerol into the medium versus the internal use of the products of photosynthesis for algal growth and (ii) that the freshwater species has a greater propensity for glycerol leakage into the external medium under saline conditions than the marine species. Furthermore, conditions that stimulated glycerol release increased the maximal rate of photosynthesis, suggesting that synthesis (from the direct products of photosynthesis) and removal of glycerol from the cell may alleviate feedback inhibition on photosynthetic capacity. The stimulation of glycerol synthesis and release by Chlamydomonas species via environmental manipulation offers an attractive option for continuous algal energy carrier production as a feedstock for biofuel generation under conditions eliminating energy carrier consumption by algal growth, while circumventing feedback inhibition of photosynthesis as well as the need for algal harvest and regrowth employed for extraction of lipid or carbohydrate feedstocks.