Improvement of light to biomass conversion by de-regulation of light-harvesting protein translation in Chlamydomonas reinhardtii

The efficient use of microalgae to convert sun light energy into biomass is limited by losses during high light illumination of dense cell cultures in closed bioreactors. Uneven light distribution can be overcome by using cell cultures with smaller antenna sizes packed to high cell density cultures, thus allowing good light penetration into the inner sections of the reactor. We engineered a new small PSII antenna size Chlamydomonas reinhardtii strain with improved photon conversion efficiency and increased growth rates under high light conditions. We achieved this goal by transformation of a permanently active variant NAB1* of the LHC translation repressor NAB1 to reduce antenna size via translation repression. NAB1* expression was demonstrated in Stm6Glc4T7 (T7), leading to a reduction of LHC antenna size by 10–17%. T7 showed a ∼50% increase of photosynthetic efficiency (ΦPSII) at saturating light intensity compared to the parental strain. T7 converted light to biomass with much higher efficiencies with a ∼50% improved mid log growth phase. Moreover, T7 cultures reached higher densities when grown in large-scale bioreactors. Thus, the phenotype of strain T7 may have important implications for biotechnological applications in which photosynthetic microalgae are used for large-scale culturing as an alternative plant biomass source.