Utilization of N-Acyl Homoserine Lactone-Secreting Bacteria in Algal Environment to Increase Biomass Accumulation of Chlorella

In the symbiotic system, bacteria can regulate the growth and metabolism of microalgae using quorum-sensing signal molecules. In this study, the response of Chlorella to N-acyl homoserine lactones (AHLs) secreted by bacteria isolated from Chlorella culture was investigated from the levels of biomass accumulation, intracellular biomacromolecule content, and antioxidant system. The results demonstrated that Agrobacterium (A-1), Brevundimonas (A-5), and Agrobacterium (A-7) with AHL activity of 26-35 Miller units isolated from Chlorella culture system, respectively, promoted the specific growth rate of microalgae by 39%, 31%, and 50% through the secretion of AHLs. Meanwhile, bacterial AHL secreting caused the increase of polysaccharides by 28-56% and proteins by 24-33% in microalgae cells. The response of antioxidant system of microalgae exposed to bacterial AHLs could be activated rapidly, with superoxide dismutase (SOD) activity increased by 1.7-2 times and malondialdehyde (MDA) content decreased by 50-61%. Moreover, compared with the direct application of exogenous AHLs, AHLs secreted by bacteria had higher efficiency of increasing microalgae biomass. This study would provide reference for further revealing the effect of bacterial quorum sensing on microalgae cultivation.