AUTHOR=Yi Xin , Chen Yunong , Cai Hongyan , Wang Jiajia , Zhang Youyu , Zhu ZhiQin , Lin Mao , Qin Yingxue , Jiang XingLong , Xu Xiaojin 

TITLE=The temperature-dependent expression of type II secretion system controls extracellular product secretion and virulence in mesophilic Aeromonas salmonida SRW-OG1

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.945000

DOI=10.3389/fcimb.2022.945000

ISSN=2235-2988

ABSTRACT=<p><italic>Aeromonas salmonicida</italic> is a typical cold water bacterial pathogen that causes furunculosis in many freshwater and marine fish species worldwide. In our previous study, the pathogenic <italic>A. salmonicida</italic> (SRW-OG1) was isolated from a warm water fish, <italic>Epinephelus coioides</italic> was genomics and transcriptomics analyzed. Type II secretion system was found in the genome of <italic>A. salmonicida</italic> SRW-OG1, while the expressions of <italic>tatA, tatB</italic>, and <italic>tatC</italic> were significantly affected by temperature stress. Also, sequence alignment analysis, homology analysis and protein secondary structure function analysis showed that <italic>tatA</italic>, <italic>tatB</italic>, and <italic>tatC</italic> were highly conservative, indicating their biological significance. In this study, by constructing the mutants of <italic>tatA, tatB</italic>, and <italic>tatC</italic>, we investigated the mechanisms underlying temperature-dependent virulence regulation in mesophilic <italic>A. salmonida</italic> SRW-OG1. According to our results, <italic>tatA</italic>, <italic>tatB</italic>, and <italic>tatC</italic> mutants presented a distinct reduction in adhesion, hemolysis, biofilm formation and motility. Compared to wild-type strain, inhibition of the expression of <italic>tatA</italic>, <italic>tatB</italic>, and <italic>tatC</italic> resulted in a decrease in biofilm formation by about 23.66%, 19.63% and 40.13%, and a decrease in adhesion ability by approximately 77.69%, 80.41% and 62.14% compared with that of the wild-type strain. Furthermore, <italic>tatA</italic>, <italic>tatB</italic>, and <italic>tatC</italic> mutants also showed evidently reduced extracellular enzymatic activities, including amylase, protease, lipase, hemolysis and lecithinase. The genes affecting amylase, protease, lipase, hemolysis, and lecithinase of <italic>A. salmonicida</italic> SRW-OG1 were identified as <italic>cyoE</italic>, <italic>ahhh1</italic>, <italic>lipA</italic>, <italic>lipB</italic>, <italic>pulA</italic>, <italic>HED66_RS01350, HED66_RS19960</italic>, <italic>aspA</italic>, <italic>fabD</italic>, and <italic>gpsA</italic>, which were notably affected by temperature stress and mutant of <italic>tatA, tatB</italic>, and <italic>tatC</italic>. All above, <italic>tatA, tatB</italic> and <italic>tatC</italic> regulate the virulence of <italic>A. salmonicida</italic> SRW-OG1 by affecting biofilm formation, adhesion, and enzymatic activity of extracellular products, and are simultaneously engaged in temperature-dependent pathogenicity.</p>