Revised phylogeny and novel horizontally acquired virulence determinants of the model soft rot phytopathogen Pectobacterium wasabiae SCC3193

PLoS Pathog. 2012;8(11):e1003013. doi: 10.1371/journal.ppat.1003013. Epub 2012 Nov 1.

Abstract

Soft rot disease is economically one of the most devastating bacterial diseases affecting plants worldwide. In this study, we present novel insights into the phylogeny and virulence of the soft rot model Pectobacterium sp. SCC3193, which was isolated from a diseased potato stem in Finland in the early 1980s. Genomic approaches, including proteome and genome comparisons of all sequenced soft rot bacteria, revealed that SCC3193, previously included in the species Pectobacterium carotovorum, can now be more accurately classified as Pectobacterium wasabiae. Together with the recently revised phylogeny of a few P. carotovorum strains and an increasing number of studies on P. wasabiae, our work indicates that P. wasabiae has been unnoticed but present in potato fields worldwide. A combination of genomic approaches and in planta experiments identified features that separate SCC3193 and other P. wasabiae strains from the rest of soft rot bacteria, such as the absence of a type III secretion system that contributes to virulence of other soft rot species. Experimentally established virulence determinants include the putative transcriptional regulator SirB, two partially redundant type VI secretion systems and two horizontally acquired clusters (Vic1 and Vic2), which contain predicted virulence genes. Genome comparison also revealed other interesting traits that may be related to life in planta or other specific environmental conditions. These traits include a predicted benzoic acid/salicylic acid carboxyl methyltransferase of eukaryotic origin. The novelties found in this work indicate that soft rot bacteria have a reservoir of unknown traits that may be utilized in the poorly understood latent stage in planta. The genomic approaches and the comparison of the model strain SCC3193 to other sequenced Pectobacterium strains, including the type strain of P. wasabiae, provides a solid basis for further investigation of the virulence, distribution and phylogeny of soft rot bacteria and, potentially, other bacteria as well.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Gene Transfer, Horizontal*
  • Multigene Family*
  • Pectobacterium / genetics*
  • Pectobacterium / pathogenicity*
  • Phylogeny*
  • Plant Diseases / genetics*
  • Plant Diseases / microbiology
  • Plant Roots / microbiology
  • Solanum tuberosum / microbiology
  • Virulence Factors / genetics*
  • Virulence Factors / metabolism

Substances

  • Virulence Factors

Grants and funding

We gratefully acknowledge the support of Academy of Finland (Center of Excellence program 2006–2011 grants no. 213509, 129628, and grants no. 136470, 120821 and 128566), University of Helsinki, Biocentrum Helsinki, Biocenter Finland, Biocenter Finland bioinformatics infrastructure network, The Finnish Doctoral Program in Plant Science, Viikki Doctoral Programme in Molecular Biosciences and Finnish Doctoral Programme in Computational Sciences, Niemi Foundation and Olvi Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.