Different organic carbon sources affect microalgal growth and extracellular polymeric substances synthesis to trigger biomass flocculation process

The addition of organic carbon sources into the culture medium represents an effective strategy for microalgae cultivation. However, its influence on the subsequent flocculation process remains poorly understood. In this study, four representative organic carbon sources were supplemented to microalgal cultures with the aim of evaluating their potential to enhance biomass accumulation, optimize fatty acid composition and improve phototolerance. The results demonstrated that the addition of ethanol, sodium acetate, glucose and fructose to the cultures resulted in extracellular protein contents of 90.9, 125.7, 67.5 and 46.0 mg/g, respectively, compared to 36.8 mg/g observed in the control culture with pure BG-11 medium. The addition of organic carbon sources led to alterations in protein content and the composition ratio of charged groups within the extracellular polymeric substances of microalgae, which in turn influenced the flocculation process. This study provides valuable insights into the selection of appropriate organic carbon sources for promoting microalgal growth and clarifies the flocculation mechanisms under various carbon utilization strategies.