Chemical mutation of Stichococcus sp. for the selection of strains with lower chlorophyll content and higher biomass production

Microalgae are photosynthetic microorganisms that can grow under a large spectrum of conditions and may produce a number of valuable products. However, increased chlorophyll concentration constitutes a limiting factor, especially in large-scale photobioreactors, causing a “shadow effect” which negatively influences biomass productivity. The main scope of the present study was to select a low chlorophyll content strain of Stichococcus sp., in order to increase light penetration into the culture of photobioreactors. Selection was through random mutation using ethyl methanesulfonate (EMS). Two promising mutants (EMS1 & EMS2) were isolated and cultivated for three generations on solid medium (petri dishes). The selected strains were then cultivated in open beaker glassware with 200 mL of F/2 medium, diluted in natural seawater, under sterile conditions. EMS1, the best performing mutant strain, exhibited lower chlorophyll (43%), higher biomass (12%), lipids (45%), and carbohydrates (28%) production, compared to the wild type. EMS1 strain proved to contain the least chlorophyll (6.29 ± 0.52 mg g ^− 1 ), yet the highest biomass (2.47 ± 0.10 g L ^− 1 ), lipids (21% of dry biomass), and carbohydrates content (44% of dry biomass) compared to the wild type strain. Protein content did not differ significantly among the strains. The mutant strain EMS1 of Stichococcus sp. has high potential for further investigation to produce biomass and various valuable bio-chemicals.