Genome Sequence of the Versatile Fish Pathogen Edwardsiella tarda Provides Insights into its Adaptation to Broad Host Ranges and Intracellular Niches

Abstract

Background Edwardsiella tarda is the etiologic agent of edwardsiellosis, a devastating fish disease prevailing in worldwide aquaculture industries. Here we describe the complete genome of E. tarda, EIB202, a highly virulent and multi-drug resistant isolate in China.Methodology/Principal Findings E. tarda EIB202 possesses a single chromosome of 3,760,463 base pairs containing 3,486 predicted protein coding sequences, 8 ribosomal rRNA operons, and 95 tRNA genes, and a 43,703 bp conjugative plasmid harboring multi-drug resistant determinants and encoding type IV A secretion system components. We identified a full spectrum of genetic properties related to its genome plasticity such as repeated sequences, insertion sequences, phage-like proteins, integrases, recombinases and genomic islands. In addition, analysis also indicated that a substantial proportion of the E. tarda genome might be devoted to the growth and survival under diverse conditions including intracellular niches, with a large number of aerobic or anaerobic respiration-associated proteins, signal transduction proteins as well as proteins involved in various stress adaptations. A pool of genes for secretion systems, pili formation, nonfimbrial adhesions, invasions and hemagglutinins, chondroitinases, hemolysins, iron scavenging systems as well as the incomplete flagellar biogenesis might feature its surface structures and pathogenesis in a fish body.Conclusion/SignificanceGenomic analysis of the bacterium offered insights into the phylogeny, metabolism, drug-resistance, stress adaptation, and virulence characteristics of this versatile pathogen, which constitutes an important first step in understanding the pathogenesis of E. tarda to facilitate construction of a practical effective vaccine used for combating fish edwardsiellosis.

Comparative proteomic study of Edwardsiella tarda strains with different degrees of virulence

“…In this work, the proteins belonging to this cycle were not detected in the E. tarda strains analysed. These results are in agreement with complete genome studies where it was not possible to detect genes related to this cycle [41] suggesting that the mechanism used by E. tarda to start the colonization can be similar to the one used by B. suis.…”

Transcriptomic dissection of the horizontally acquired response regulator EsrB reveals its global regulatory roles in the physiological adaptation and activation of T3SS and the cognate effector repertoire inEdwardsiella piscicidaduring infection toward turbot

“…Interestingly, this consensus sequence is highly conserved in the previously established SsrB binding motifs of Salmonella enterica and Sodalis glossinidus 33 ; both of these species belong to a neighboring genus of Edwardsiella bacteria. 5 The 18-bp consensus motif also contains 7-4-7 architecture with ATCGGGT palindrome repeats and is similarly localized to the promoter region of T3SS genes, i.e., esrC, esaM, escC, and esaR, as well as the effector gene (ETAE_1586) (Fig. 4G and H).…”

“…5,6 In the T3SS gene cluster, the concomitant 2-component system (TCS) EsrA-EsrB is essential for the bacterium's pathogenesis. 6,31 To better decipher the regulatory roles and the regulatory mechanisms of the response regulator EsrB, we performed RNA-seq analysis with EIB202 and DesrB RNA isolated from LB (n D 3) and DMEM cultures (n D 3) and compared their differential gene expression.…”

“…3 Elucidating the genes controlled by TCS will facilitate the understanding of the mechanisms underlying TCS scouting of environmental/host cues and switching gene expression and ultimately lead to the development of antibacterial therapies. 4 Edwardsiella piscicida (formerly included in E. tarda), 5,6,7,8 a member of the Enterobacteriaceae, colonizes a broad range of hosts including fish and mammals and causes fatal hemorrhagic septicemia and gastro-and extra-intestinal infections. 9,10,11,12 As a leading pathogen that threats fresh and seawater aquaculture farms, E. piscicida causes huge economic losses to the world aquaculture industry, especially for farmed flatfish (turbot and flounder).…”

“…5 Systematic mutation of the single RR gene reveals that EsrA-EsrB is the most essential TCS in E. piscicida pathogenesis. 31 Like their counterparts SsrA, SsrB and SPI-2 in Salmonella, 32,33,34 EsrA and EsrB and the associated T3SS locus may be horizontally acquired and may have evolved to coordinate the expression of virulence and adaptation to host microenvironments by the reprogramming of ancestral genes unlinked to the T3SS locus.…”