Role and Regulation of the Flp / Tad Pilus in the Virulence of Pectobacterium atrosepticum SCRI 1043 and Pectobacterium wasabiae SCC 3193

In this study, we characterized a putative Flp/Tad pilus-encoding gene cluster, and we examined its regulation at the transcriptional level and its role in the virulence of potato pathogenic enterobacteria of the genus Pectobacterium. The Flp/ Tad pilus-encoding gene clusters in Pectobacterium atrosepticum, Pectobacterium wasabiae and Pectobacterium aroidearum were compared to previously characterized flp/tad gene clusters, including that of the well-studied Flp/Tad pilus model organism Aggregatibacter actinomycetemcomitans, in which this pilus is a major virulence determinant. Comparative analyses revealed substantial protein sequence similarity and open reading frame synteny between the previously characterized flp/tad gene clusters and the cluster in Pectobacterium, suggesting that the predicted flp/tad gene cluster in Pectobacterium encodes a Flp/Tad pilus-like structure. We detected genes for a novel two-component system adjacent to the flp/tad gene cluster in Pectobacterium, and mutant analysis demonstrated that this system has a positive effect on the transcription of selected Flp/Tad pilus biogenesis genes, suggesting that this response regulator regulate the flp/tad gene cluster. Mutagenesis of either the predicted regulator gene or selected Flp/Tad pilus biogenesis genes had a significant impact on the maceration ability of the bacterial strains in potato tubers, indicating that the Flp/Tad pilus-encoding gene cluster represents a novel virulence determinant in Pectobacterium. Soft-rot enterobacteria in the genera Pectobacterium and Dickeya are of great agricultural importance, and an investigation of the virulence of these pathogens could facilitate improvements in agricultural practices, thus benefiting farmers, the potato industry and consumers. Citation: Nykyri J, Mattinen L, Niemi O, Adhikari S, Kõiv V, et al. (2013) Role and Regulation of the Flp/Tad Pilus in the Virulence of Pectobacterium atrosepticum SCRI1043 and Pectobacterium wasabiae SCC3193. PLoS ONE 8(9): e73718. doi:10.1371/journal.pone. 0073718 Editor: Ching-Hong Yang, University of Wisconsin-Milwaukee, United States of America Received May 17, 2013; Accepted July 22, 2013; Published September 9, 2013 Copyright: 2013 Nykyri et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The authors gratefully acknowledge the support of Academy of Finland grant no. 128566, University of Helsinki, The Finnish Doctoral Program in Plant Science, The Viikki Doctoral Programme in Molecular Biosciences, The Niemi Foundation (Koisjärvi, Finland), The Finnish Cultural Foundation, The Olvi Foundation (Iisalmi, Finland), The Future Fund (University of Helsinki) and Department of Agricultural Sciences, the Estonian Science Foundation Grant SF0180088s08. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: minna.pirhonen@helsinki.fi