Bacillus cereus LS2 from Apostichopus japonicus antagonizes Vibrio splendidus growth

Abstract In this study, a bacterium identified as Bacillus cereus LS2 was isolated from healthy sea cucumbers and possessed strong antagonistic activity toward Vibrio splendidus, an important pathogen to Apostichopus japonicus. The antagonistic activity of strain LS2 to the growth of V. splendidus was 86.83% ± 1.47%. The antagonistic substance, with molecular weight less than 3 kDa, was sensitive to trypsin but stable at high temperatures. The antagonistic substances could be precipitated by acid and dissolved in anhydrous methanol. Further, the in-situ hydrolysis and ninhydrin staining assay showed that the antagonistic substance was a peptide. On the basis of these characteristics, the antagonistic substance was postulated to be a kind of lipopeptide. The analysis of differentially expressed proteins revealed that the expression of dihydrolipoamide dehydrogenase 1 (DLDH1) in V. splendidus could be upregulated in the presence of the LS2 supernatant. Furthermore, the overexpression of DLDH1 reduced the growth of V. splendidus by 12.5% compared with that of the wild-type strain. Our findings suggest that LS2 could be used as a potential bacterial antagonist to control V. splendidus infections by upregulating the DLDH1 expression in V. splendidus.