Selection and fluorescence based screening of algal strains for temperature tolerance and increased productivity for industrial scale cultivation

Abstract

Microalgae are emerging as a viable source of sustainable energy and bioproducts due to their rapid growth and capacity to produce valuable products. Their ability to grow in diverse, non-arable environments while minimizing resource use makes them a promising alternative to traditional crops for biofuel, feedstock, and other value-added products. Industrial-scale outdoor cultivation of microalgae subjects cells to dynamic environmental conditions such as fluctuating temperatures that can influence growth and biomass accumulation. This makes selecting a strain that can maintain high productivity crucial for industrial-scale cultivation. The first aim of this thesis was to compare the growth and biomass accumulation of ten strains that were known for their high productivities in temperatures ranging from 18°C to 30°C. Of the ten selected strains, Scenedesmus rubescens NREL 46B-D3 and Monoraphidium minutum 26B-AM were determined to have the best overall growth performance in both temperatures and the highest biomass accumulation when grown at 30°C. S. rubescens and M. minutum exhibited an 88.5% and 22.6% higher average total organic carbon accumulation compared to the next highest performing strain tested. The second aim of this thesis was to utilize gamma irradiation mutagenesis to generate mutants with improved biomass accumulation. Optimal LD90% dosages of 300 Gy and 75 Gy were determined for S. rubescens and M. minutum respectively. 3135 and 3356 putative mutants were characterized for S. rubescens and M. minutum, respectively. A fluorescence-based screening approach was used to screen for putative mutants with altered photophysiology traits correlated with photosynthetic efficiency. A total of 37 S. rubescens putative mutants and 14 putative M. minutum mutants demonstrated repeated photophysiological alterations and were selected for growth comparisons between their wild type counterparts. Only one putative M. minutum mutant, MRM J-325, demonstrated improvements in specific growth rate compared to wild type. This assumed mutant will be scaled up for biomass accumulation experiments at large scale.