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

Abstract

Aeromonas salmonicida is a well-known cold-water pathogenic bacterium. Previously, we reported the first isolation of pathogenic A. salmonicida from diseased Epinephelus coioides, 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 A. salmonicida SRW-OG1 at 18, 28, and 37 °C was analyzed. The transcriptome of A. salmonicida SRW-OG1 at different temperatures showed a clear separation boundary, which might provide valuable information for the temperature adaptation and virulence regulation of A. salmonicida SRW-OG1. Interestingly, aerA and hlyA, 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 Aeromonas strains, the induction of aerA and hlyA was associated with the mesophilic virulence. Further study proved that the extracellular products (ECPs) purchased from A. salmonicida SRW-OG1 cultured at 28 and 37 °C showed elevated hemolytic activity and virulence than those at 18 °C. Moreover, the silence of aerA and hlyA led to significantly decreased hemolysis and virulence. Taken together, our results revealed that the mesophilic virulence of A. salmonicida SRW-OG1 might be due to the enhanced expression of aerA and hlyA induced by elevated temperatures.

Comparative genomic analysis provides insights into taxonomy and temperature adaption of Aeromonas salmonicida

“…T2SS functions as a transport mechanism to translocate proteins (such as aerolysin, proteases, DNases and amylases) from the periplasm to the extracellular environment in Aeromonas (Li et al, 2011; Seshadri et al, 2006), and the ExeAB homologue GspAB complex has been demonstrated to be functional in the assembly of the T2SS secretin multimer in A. salmonicida (Strozen et al, 2011). The haemolytic genes aerA and hlyA have been found to be significantly up‐regulated in mesophilic A. salmonicida SRW‐OG1 grown at 28 and 37°C compared to 18°C (Chen et al, 2022), and the haemolytic activity of A. salmonicida is enhanced by elevated incubation temperature or limited iron (Chen et al, 2022; Kroniger et al, 2022). It can be thought that these common virulence factors constitute the basic virulence of A. salmonicida .…”

“…. In particular, it is worth noting that, more and more studies in China on infection (Lian et al, 2020;Meng et al, 2020;Wang et al, 2020), pathogenicity (Chen et al, 2022;Meng et al, 2017;Yi et al, 2022) and interaction with hosts of A. salmonicida (Huang, Qi, Zuo, Alias, & Xu, 2020;Long et al, 2015;Xia et al, 2022;Xue et al, 2021) have been reported in recent years, implying the popularity and importance of this bacterium in China.…”

Virulence regulation of Zn2+ uptake system znuABC on mesophilic Aeromonas salmonicida SRW-OG1

“…According to our recently published study, the A. salmonicida SRW-OG1 contains the aerolysin and hemolysin ( 5 ). In the present study, the hemolysis activity of A. salmonicida SRW-OG1 wild-type, znuA -RNAi, znuB -RNAi and znuC -RNAi strains were compared.…”

“…The isolation of C947 strains from patients with acute gastroenteritis and the isolation of AJ83 strains from patients with post-traumatic cellulitis of the foot ( 12 ). Based on pathogen-host interaction factor analysis by Qi et al ( 13 ) against A. salmonicida SRW-OG1, C947, and AJ83 strains and transcriptome data analysis by Chen et al ( 5 ) on A. salmonicida SRW-OG1 at different temperatures, A. salmonicida SRW-OG1 has a great potential to infect mammals and humans. Notably, the remarkably high expression of znuA, znuB , and znuC genes at 18 and 37°C also indicated that they might be related to the pathogenesis under different temperatures.…”

“…Aeromonas salmonicida is a facultative anaerobic Gram-negative bacterium, widely existing in aquatic environments and soils ( 1 ), which can cause furunculosis in a variety of marine and freshwater fish, especially salmon ( Salmonidae ) and carp ( Cyprinidae ), as well as rainbow trout ( Onco-rhynchus mykiss ), turbot ( Scophthalmus maximus L . ), carp ( Cyprinus carpio ), goldfish ( Carassius auratus ) and so on ( 2 – 5 ). Since A. salmonicida has been proven unable to grow above 25°C, and most of them are isolated from cold water teleost fish ( 6 – 8 ), researchers believe that A. salmonicida cannot infect mammals and humans for quite a long time ( 9 , 10 ).…”