Improved biomass production of a microalga through adaptative laboratory evolution to a high light environment

Microalgae produce a wide range of biomolecules with commercial applications and thus maximizing algal productivity in these systems is of central importance. Although, photosynthesis requires light, microalgae have limited productivity when their photosystem is exposed to excessive light irradiance and become photoinhibited. Here, we perform adaptative laboratory evolution to improve the light harvesting efficiency of Chlamydomonas reinhardtii under high irradiance. In doing so, we also test whether manipulating the genetic variation of the lineages under selection, through UV mutagenesis, or creating mixed strains with a single, or five generations of recombination prior to selection, increases the evolutionary response. Our results indicate that selection under high light increases total pigment production and the ratios of carotenoids to chlorophyll-a and chlorophyll-a to chlorophyll-b. These changes likely increase photoprotection and make the photosystem more efficient by reducing the size of light-harvesting antennae. Measurements of the maximum potential quantum efficiency of Photosystem II suggest that high light intensity selected lines were more stressed under normal light conditions indicative of a trade-off between light environments. Contrary to expectations, we found that different strains responded equally to selection, irrespective of whether they were single or mixed strains or pre-treated with UV radiation. Our study provides further evidence of the utility of adaptative laboratory evolution as a tool for enhancing biomass production and high-light resistance in C. reinhardtii and suggests that significant evolutionary responses can be achieved without the need for mixing or inducing mutations through UV radiation.