Effects of surfactants on fermentation of Streptomyces galilaeus AF1

Objective  To study the effects of surfactants on fermentation of Streptomyces galilaeus AF1 strain.

Method  The single factor experiments were performed to optimize the surfactant type and the initial concentration and determine the best adding time. The Box-Behnken test design and response surface analysis were used to determine the most appropriate concentrations of surfactants. Flow cytometer instrument was used to measure the cell fluorescence intensity and investigate the effects of surfactant on cell membranes of AF1.

Result  The optimum concentrations of added surfactants were 8.95 g·L^–1 Tween-80, 2.09 g·L^–1 Triton X-100 and 3.89 g·L^–1 sorbitol. The best adding time was five days after inoculation. The membrane permeability test results showed that the cell fluorescence intensity of AF1 of the test group was significantly higher than that of the control group.

Conclusion  The response surface model explained 94.89% of the variation in the dependent variables and therefore had practical significance. Membrane permeability of the AF1 strain significantly increased after adding the optimal surfactants complex, which led to increased efflux of intracellular active substance and biosythesis of antibacterial substance.