Abstract:This study aimed to investigate the regularity of N-acyl homoserine lactone (AHL) secretion by spoilage bacteria Hafnia alvei H4 isolated from ready-to-eat sea cucumber, and the influence of environmental factors on AHL secretion. AHL content secreted by H4 were determined using Chromobacterium violaceum CV026, and AHL activity was detected by Agrobacterium tumefaciens KYC55 in a β-galactosidase assay. The results showed that the content and activities of AHLs secreted by H4 were density-dependent. AHL activity initially increased, and then decreased with time under appropriate culture conditions, reaching a maximum in the late logarithmic phase (OD600??1.6; pH??5.71). Testing for the influence of environmental factors on AHL secretion revealed that an increased concentration of sodium chloride promoted the secretion of AHLs by H4 within a certain concentration range. Secretion of AHLs was reduced under weakly acidic and alkaline environments, and AHL content was the highest when the environmental pH was 7.0. The optimum temperature for AHL secretion by H4 was found to be 30°C, and the ability of H4 to secrete AHLs was reduced at low temperatures. The ability of H4 to secrete AHLs was significantly different upon usage of different carbon or nitrogen sources; activities were the highest when fructose was used as the carbon source and ammonium sulfate as the nitrogen source. In conclusion, the quorum sensing system of Hafnia alvei H4 was density-dependent, influenced by environmental factors, and showed regular changes.
