Ecological engineering helps maximize function in algal oil production.

Algal biofuels have the potential to curb emissions of greenhouse gases from fossil fuels, but current growing methods fail to produce fuels that meet the multiple standards necessary for economical industrial use. For example, algae grown as monocultures for biofuel production have not simultaneously and economically achieved high yields of the high-quality, lipid-rich biomass desired for the industrial-scale production of bio-oil. Decades of study in the field of ecology have demonstrated that simultaneous increases in multiple functions, such as the quantity and quality of biomass, can occur in natural ecosystems by increasing biological diversity. Here we show that species consortia of algae can improve the production of bio-oil, which benefits from both high biomass yield and high quality of biomass rich in fatty acids. We explain the underlying causes of increased quantity and quality of algal biomass among species consortia by showing that, relative to monocultures, species consortia can differentially regulate lipid metabolism genes while growing to higher levels of biomass, in part due to greater utilization of nutrient resources. We identify multiple genes involved in lipid biosynthesis that are frequently upregulated in bicultures, and further show that these elevated levels of gene expression are highly predictive of the elevated levels in biculture relative to monoculture of multiple quality metrics of algal biomass. These results show that interactions between species can alter the expression of lipid metabolism genes, and further demonstrate that our understanding of diversity-function relationships from natural ecosystems can be harnessed to improve production of bio-oil. Importance section: Algal biofuels are one of the more promising forms of renewable energy. In our study, we investigate whether ecological interactions between species of microalgae regulate two important factors in cultivation - the biomass of the crop produced and quality of the biomass that is produced. We find that species interactions often improved production yields, especially the fatty acid content of the algal biomass, and that differentially expressed genes involved in fatty acid metabolism are predictive of improved quality metrics of bio-oil. Other studies have found that diversity often improves productivity and stability in agricultural and natural ecosystems. Our results provide further evidence that growing multi-species crops of microalgae may improve the production of high-quality biomass for bio-oil.