Generation and characterization of reduced PSII antenna size mutants of Chlorella sorokiniana for improved biomass

Biofuel production from algal biomass is a fundamental component in developing sustainable energy sources that can replace fossil fuels. However, cost effectiveness needs to be taken into account as there is substantial difference between the higher cost of biofuel production and relatively low cost of fossil fuels. Studies on Chlorella species have focussed on improving algal biomass production capacity. One of the critical problems is inefficient use of light caused by its unequal distribution. The current study describes the development of photosynthetic Chlorella sorokiniana mutants by EMS mutagenesis. Mutagenesis and visual phenotypic selection procedures were applied and three C. sorokiniana chlorophyll mutants (CSCM) have been identified. The selected CSCM8, CSCM10 and CSCM21 mutant strains show diverse phenotypes with 33-47% reduced chlorophyll content. Further characterization reveal that these selected mutants had 23-44% reduced antenna size, improved effective quantum yield of PSII [Y(II)], reduced regulated (light-activated) energy dissipation Y(NPQ), and reduced non-photochemical quenching (NPQ). Moreover, the characterised mutants in the laboratory have shown 19-34% and 13-29% increased biomass productivity under low light and high light conditions (50 and 250 mu mol photons m(-2) s(-1)), respectively. This study indicates that genetic modification of C. sorokiniana with smaller antenna size can improve biomass content; further, these mutants can be used for strain improvement having higher lipid content.