N-3-Oxo-octanoyl-homoserine lactone as a promotor to improve the microbial flocculant production by an exopolysaccharide bioflocculant-producing bacterium Agrobacterium tumefaciens F2

Abstract

This study showed that Agrobacterium tumefaciens F2 could produce N-3-oxo-octanoyl-homoserine lactone (3-oxo-C8HSL), one of the N-acyl-homoserine lactone (AHL) class of microbial quorum-sensing signaling molecules. After the addition of exogenous 3-oxo-C8HSL, the exopolysaccharide concentration of microbial flocculants improved by 1.4 times. Fermentation conditions for adding 3-oxo-C8HSL were further optimized by response surface methodology. The optimal fermentation conditions were 0.22 μM 3-oxo-C8HSL at 30.36 °C and an initial pH of 8.11. The corresponding exopolysaccharide concentration reached 556.49 mg L⁻¹, and the flocculating rate was 91.54%. The microbial flocculant production increased by 1.55 times and the flocculation efficiency increased by 10.96% under these fermentation conditions. Results demonstrated that the microbial flocculant production was regulated by AHL-mediated quorum sensing mechanisms in A. tumefaciens F2.