Phosphate content affecting the heterotroph population and phosphate distribution in photosynthetic biomass

The description is adapted from the manuscript we will submit for peer-reviewed journal publication.During the culturing of microalgae, heterotrophic bacteria can compete for nutrients, compromise the quality of the harvested biomass, or cause culture crashes. We systematically investigated the effects of depleting inorganic phosphate (Pi) on the growth of the cyanobacterium Synechocystis sp. PCC 6803, its community of heterotrophic bacteria, and the biomass’s chemical composition. On the one hand, depleting Pi had minimal impact on the production of total biomass, extracellular polymeric substances (ESP), soluble microbial products (SMP), and most types of intracellular organic polymers. On the other hand, depleting Pi led to markedly less lipid content, less heterotrophic biomass, and a shift in the heterotrophic community from Burkholderiales to Sphingobacteriales and Saprospirales. The causes of the large impacts were that Synechocystis was much better at scavenging a very low Pi concentration and could adapt by lowering its phosphorus content. This work lays a foundation for controlling the accumulation of heterotrophs and reducing their deleterious effects in microalgae culturing.