Abstract: The aim of this study was to evaluate the regulation of quorum sensing on biofilm formation and swimming motility of Hafnia alvei H4 isolated from spoiled instant sea cucumber. Both the luxR and luxI genes were knocked out to construct the mutant strain ΔluxRI. Crystal violet staining method was used to measure the biofilm formation of H. alvei H4, and the structure of the biofilm was observed by scanning electron microscopy (SEM). In addition, the spread plate assay was used to detect swimming motility. The relative expression levels of biofilm- and motility-related genes (flgA, flgE, fliA, flhD and flhC) were measured by real-time PCR method. Results showed that growth of H. alvei H4 was not affected by depletion of the luxRI genes. However, AHLs production was found deficient in the ΔluxRI strain. In addition, biofilm formation of ΔluxRI was significantly inhibited (P < 0.05), and fewer cells were observed compared with the wild-type strain by SEM on the medium, and fewer reticular structures were formed by exopolysaccharides (EPS) from ΔluxRI. Furthermore, swimming motility of ΔluxRI was found to be obviously decreased. The relative expression levels of the flgA, flgE, fliA, flhD and flhC genes were significantly (P < 0.05) reduced. Therefore, a conclusion can be drawn that biofilm formation and swimming motility of H. alvei H4 is regulated by quorum sensing.

Key words: Hafnia alvei; quorum sensing; biofilm formation; swimming motility