Enhanced Hemolytic Activity of Mesophilic SRW-OG1 Is Brought about by Elevated Temperatures.

is a well-known cold-water pathogenic bacterium. Previously, we reported the first isolation of pathogenic from diseased , a kind of warm-water fish, and it was proved to be a putative mesophilic strain with potent pathogenicity to humans. In order to investigate the mechanisms underlying mesophilic growth ability and virulence, the transcriptome of SRW-OG1 at 18, 28, and 37 °C was analyzed. The transcriptome of SRW-OG1 at different temperatures showed a clear separation boundary, which might provide valuable information for the temperature adaptation and virulence regulation of SRW-OG1. Interestingly, and , the hemolytic genes encoding aerolysin and hemolysin, were found to be significantly up-regulated at 28 and 37 °C. Since aerolysin and hemolysin are the most well-known and -characterized virulence factors of pathogenic strains, the induction of and was associated with the mesophilic virulence. Further study proved that the extracellular products (ECPs) purchased from SRW-OG1 cultured at 28 and 37 °C showed elevated hemolytic activity and virulence than those at 18 °C. Moreover, the silence of and led to significantly decreased hemolysis and virulence. Taken together, our results revealed that the mesophilic virulence of SRW-OG1 might be due to the enhanced expression of and induced by elevated temperatures.