Evolution of virulence in a novel family of transmissible mega‐plasmids

Abstract

Some Serratia entomophila isolates have been successfully exploited in biopesticides due to their ability to cause amber disease in larvae of the Aotearoa (New Zealand) endemic pasture pest, Costelytra giveni. Anti-feeding prophage and ABC toxin complex virulence determinants are encoded by a 153-kb single-copy conjugative plasmid (pADAP; amber disease-associated plasmid). Despite growing understanding of the S. entomophila pADAP model plasmid, little is known about the wider plasmid family. Here, we sequence and analyse mega-plasmids from 50 Serratia isolates that induce variable disease phenotypes in the C. giveni insect host. Megaplasmids are highly conserved within S. entomophila, but show considerable divergence in Serratia proteamaculans with other variants in S. liquefaciens and S. marcescens, likely reflecting niche adaption. In this study to reconstruct ancestral relationships for a complex mega-plasmid system, strong coevolution between Serratia species and their plasmids were found. We identify 12 distinct megaplasmid genotypes, all sharing a conserved gene backbone, but encoding highly variable accessory regions including virulence factors, secondary metabolite biosynthesis, Nitrogen fixation genes and toxin-antitoxin systems. We show that the variable pathogenicity of Serratia isolates is largely caused by presence/absence of virulence clusters on the megaplasmids, but notably, is augmented by external chromosomally encoded factors.

Genome sequence of the entomopathogenic Serratia entomophila isolate 626 and characterisation of the species specific itaconate degradation pathway

“…Annotation and overview of the Serratia entomophila 626 genome The S. entomophila 626 genome sequence comprises one complete chromosomal contig and a single plasmid contig, the latter previously annotated by Sitter et al (15). The S. entomophila isolate 626 chromosome comprised of 5,046,461 bp, of a comparable size to S. grimesii (5,072,299 bp) but smaller than S. proteamaculans (5,593,263 bp, Table 1).…”

“…To date, only single isolations of S. entomophila from outside New Zealand, in France, Mexico, and India, have been reported (10)(11)(12). Restriction enzyme pro le assessment of the chromosomes and plasmids of C. giveni active strains revealed isolates of S. entomophila appeared to be genetically conserved while those of S. proteamaculans were more varied (13)(14)(15). Unique to S. entomophila is its ability to utilize itaconate, which can be used to differentiate S. entomophila from other Serratia species (11,16).…”

Genome sequence of the entomopathogenic Serratia entomophila isolate 626 and characterisation of the species specific itaconate degradation pathway

“…The S. entomophila 626 genome sequence comprises one complete chromosomal contig and a single plasmid contig, the latter previously annotated by Sitter et al [15]. The S. entomophila isolate 626 chromosome comprised of 5,046,461 bp, of a comparable size to S. grimesii (5,072,299 bp) but smaller than S. proteamaculans (5,593,263 bp, Table 1).…”

“…To date, only single isolations of S. entomophila from outside New Zealand, in France, Mexico, and India, have been reported [10][11][12]. Restriction enzyme profile assessment of the chromosomes and plasmids of C. giveni active strains revealed isolates of S. entomophila appeared to be genetically conserved while those of S. proteamaculans were more varied [13][14][15].…”

In silico characterization of IncX3 plasmids carrying blaOXA-181 in Enterobacterales

“…Conjugative plasmids are important vehicles for the dissemination of antibiotic resistant genes (ARGs) ( Smillie et al., 2010 ; Ravi et al., 2018 ). These plasmids typically have the conserved backbone regions and the variable accessory regions ( Brown et al., 2013 ; Sitter et al., 2021 ). The former contains genes encoding plasmid-related traits, such as replication control and conjugation functions, while the latter have accessory genes, such as genes encoding antibiotic resistance, which are usually located on the transposons or integrons ( Norman et al., 2009 ; Norberg et al., 2011 ).…”