Enhancement of carotenoids by mutation and stress induced carotenogenic genes in Haematococcus pluvialis mutants

Growing culture of green alga Haematococcus was exposed to mutagens such as UV, ethyl methane sulphonate (EMS) and 1-methyl 3-nitro 1-nitrosoguanidine (NTG), and further screened over herbicide - glufosinate. The survival rate of cells decreased with increasing concentration of mutagens and herbicides. The mutants exhibited 23–59% increase in total carotenoid and astaxanthin contents. The NTG treated glufosinate resistant mutant showed increased (2.2% to 3.8% w/w) astaxanthin content. The transcript levels of phytoene synthase, phytoene desaturase, lycopene cyclase, β-carotene ketolase and β-carotene hydroxylase enzymes in the mutant cultures were found to be 13-18, 14-17, 3, 3-22 and 6-20 fold higher respectively compared to wild type. The mutant obtained by UV irradiation showed highest lycopene cyclase activity (458 nmole β-carotene formed/mg protein/h) followed by NTG mutant (315 nmole β-carotene formed/mg protein/h) when compared to that of parent strain (105 nmole β-carotene formed/mg protein/h). Expression analysis of carotenoid biosynthetic genes in the mutants exhibited increase in transcript levels compared to wild type.