Evaluating Marinichlorella kaistiae KAS603 cell size variation, growth and TAG accumulation resulting from rapid adaptation to highly diverse trophic and salinity cultivation regimes

Abstract

The ability of a microalgal species to adapt to changes in cultivation environment is likely to be beneficial for a successful biofuel/bioproduct production system, because the species could maintain high yields under diverse seasonal or cultivation conditions. Examining factors that enable culturing flexibility in a single species could provide clearer insights than when comparing different species because it will reduce interspecies variability. Marinichlorella kaistiae KAS603 is an excellent model to evaluate mechanisms involved in adaptation to different cultivation regimes. We have studied cell growth, size, triacylglycerol (TAG) accumulation and life cycle stages in this multiple fission dividing strain under a wide variety of conditions, ranging from autotrophic growth in freshwater to mixotrophic growth in fresh and seawater, and to autotrophic growth under saline and hypersaline conditions. Such conditions influence the division mode of the strain, which is linked to biomass and TAG yield. Based on lab and pilot plant experiments, we have discovered that the fastest TAG accumulation takes place under mixotrophy in freshwater, highest yield (culture density plus TAG) condition occurs under mixotrophy in sea water, and the best outdoor culture condition to achieve growth with fewer invasive species is hypersaline natural seawater. In addition to characterizing growth and TAG accumulation characteristics under a wide variety of cultivation conditions, this work sets the stage for investigation into the mechanisms that enable diverse cultivation adaptations, and contribute to the development of this environmentally flexible microalga as a production feedstock.