Quorum sensing inhibitory activity and fermentation condition optimization of crude extract of the marine bacterial strain Vibrio sp. LA-05

Abstract:

[Background] The metabolites of marine microorganisms are considered ideal sources for discovering natural active substances, which inevitably include novel quorum sensing inhibitors (QSIs). Response surface method uses multivariate quadratic regression model to fit the relationship between each factor and response value and evaluate the effects of factors and their interaction, which can effectively screen out the best conditions of the factors affecting the microbial fermentation for metabolite production. [Objective] The quorum sensing inhibitory activity of the crude extract of the marine bacterial strain Vibrio sp. LA-05 was investigated with Chromobacterium violaceum ATCC 12472^T as the indicator strain. To improve the production of active substances in the crude extract, we employed response surface method to optimize the fermentation conditions of the strain on the basis of single factor experiments. [Methods] After preliminarily screening by the agar plate diffusion method, the growth curves and violacein production of C. violaceum ATCC 12472^T were employed to evaluate the quorum sensing inhibitory activity of the crude extract. On the basis of single factor experiments, fermentation conditions were optimized by Box-Behnken design and response surface method with violacein inhibition rate as a response value to improve the production of active substances in the crude extract. [Results] Within the concentration range that did not affect the growth of C. violaceum ATCC 12472^T, the crude extract inhibited the production of violacein to various degrees. The fermentation conditions were optimized as fermentation with the inoculum amount of 2.37% at 19.28 ℃ and 154.21 r/min for 37.59 h, the extract obtained under which had the expected inhibition rate of 53.38%. The verification experiment showed that the inhibition rate of violacein was 52.85%±0.64%, close to the model predicted value. This result indicated that the regression model had a good fitting degree with the experimental results, being reliable and feasible. [Conclusion] The crude extract of the marine bacterial strain Vibrio sp. LA-05 possesses quorum sensing inhibitory activity. The fermentation conditions of this strain are optimized by response surface method, which will lay a foundation for the research and development of novel QSIs.