To Be or Not to Be Mesophilic, That Is the Question for Aeromonas salmonicida

Abstract

The bacterium Aeromonas salmonicida has long been known to be one of the most feared pathogens in fish farming. However, the more we discover about this bacterial species, the more we question whether it is really exclusively an aquatic pathogen. In recent years, it has become obvious that this bacterial species includes a myriad of strains with various lifestyle and ecological niches, including the well-known strict psychrophiles, the first bacteria known of the species, and the newly described mesophilic strains. The mesophiles are able to grow at low temperatures, but even better at temperatures of approximately 37 °C, which strict psychrophiles cannot do. In this perspective article, we address some aspects surrounding this dual lifestyle in A. salmonicida, including the impact of mobile genetic elements, and how future research around this bacterial species may focus on the psychrophilic/mesophilic dichotomy, which makes A. salmonicida an increasingly interesting and relevant model for the study of speciation.

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

“…The ANI heatmap and core‐genome phylogenetic tree both revealed that the 25 A. salmonicida strains clustered into three independent groups. As proposed in the previous studies, A. salmonicida can be classified into ‘typical’ and ‘atypical’ based on whether the strain belongs to subspecies salmonicida or not (Dallaire‐Dufresne et al, 2014; Garcia et al, 2000; Wiklund & Dalsgaard, 1998), or into ‘mesophilic’ and ‘psychrophilic’ based on whether the strain can grow at 37°C or not (Vincent & Charette, 2022). Obviously, neither of these two classification rules is suitable for the three independent A. salmonicida groups in this study.…”

“…Apart from vapA , genes ( xpsE , xpsD and gspF ) encode type II secretion system‐related proteins, and genes ( rfbC , btuD3 , sacA , gnu and tagO ) encode some enzymes such as epimerases and transferases were also found in the gene cluster. It is supposed that the psychrophilic strains appear to evolve from mesophilic strains with some abilities lost or acquired to strict psychrophilic restrained lifestyle, and genes could be acquired by bacteria, resulting in the loss of the mesophilic phenotype and a gain in virulence (Vincent & Charette, 2022). Therefore, a speculation is that proteins encoded by the two unique gene clusters may play important roles in adaption of the psychrophilic strains to their specific hosts, namely cold water fish and further experiments are needed to verify it.…”

“…Although A. salmonicida has been thoroughly studied in its pathogenesis, treatments and interaction with hosts, the differences and pathogenic mechanisms of the psychrophilic and mesophilic groups are still unknown for limited information on The ANI heatmap and core-genome phylogenetic tree both revealed that the 25 A. salmonicida strains clustered into three independent groups. As proposed in the previous studies, A. salmonicida can be classified into 'typical' and 'atypical' based on whether the strain belongs to subspecies salmonicida or not (Dallaire-Dufresne et al, 2014;Garcia et al, 2000;Wiklund & Dalsgaard, 1998), or into 'mesophilic' and 'psychrophilic' based on whether the strain can grow at 37°C or not (Vincent & Charette, 2022). Obviously, neither of these two classification rules is suitable for the three independent…”

An Outbreak of Aeromonas salmonicida in Juvenile Siberian Sturgeons (Acipenser baerii)

“…Lesions of furunculosis and septicaemia caused by A. salmonicida have been described in a great variety of fish, causing high mortality outbreaks [13][14][15][16]. Moreover, its zoonotic potential is highlighted by the reports of human infections caused by mesophilic strains [17][18][19][20].…”

Aeromonas salmonicida: Genomics, Taxonomy, Diversity, Pathogenesis, Treatments and Beyond

“…Since then, thanks to the use of omics methods, the species A. salmonicida has revealed part of its greatly underestimated diversity. A perspective article on this subject opens this Special Issue, entitled Aeromonas salmonicida : Genomics, Taxonomy, Diversity, Pathogenesis, Treatments and Beyond [ 2 ]. The introductory article describes the new dichotomy found within the species A. salmonicida ; on one side are the four classically described psychrophilic subspecies ( salmonicida , smithia , achromogenes , and masoucida ), and on the other are an increasing number of mesophilic strains that are capable of growing at temperatures of 37 °C and even higher, but also at lower temperatures like psychrophilic strains.…”