Acyl-homoserine lactones regulate the photosynthesis of Chlorella sorokiniana to promote biomass and lipid

In the phycosphere, quorum sensing molecules (QSMs) might mediate an intricate interaction between microalgae and specified bacteria, yet little research had been reported in this area. In this study, the impacts of QSMs excreted by microalgae growth-promotion bacteria (MGPB) on Chlorellla sorokiniana were analyzed from phenotype and genes expression. In the control, the biomass and lipid content of C. sorokiniana were 93.06 mg/L and 37.58% after 15 days of cultivation. By adding 50 nmol L-1 of N-Octanoyl-DL-homoserine lactone (C8-HSL) and N-Tetradecanoyl-DL-homoserine lactone (C14-HSL) to the microalgae cultivation medium respectively, the biomass was raised by 7.42% and 13.86%, and the lipid contents were raised by 11.31% and 21.87%. The C8HSL and C14-HSL could also enhance the photosynthesis of C. sorokiniana. After treated by 50 nmol L-1 of C8HSL and C14-HSL, the maximum photosynthetic rates (Pm) were 17.80% and 28.81% higher than the control (the Pm was 2.36 mu mol O2 mg- 1 Chla min- 1), and the light compensation points (Ic) were 1.88- and 1.67-fold increases compared to the control (the Ic was 27.23 mu mol m- 2 s- 1). Furthermore, a total of 753 genes showed significant difference in expression, and the analysis of gene related to photosystem, chlorophyll synthesis and electron transport chains verified that acyl-homoserine lactones mediated the expression of photosynthesisrelated genes. This study revealed the signaling communication mechanism between microalgae and bacteria, thereby guiding the regulation depending on QSMs.