High genomic variability in the plant pathogenic bacterium Pectobacterium parmentieri deciphered from de novo assembled complete genomes

Abstract Background Pectobacterium parmentieri is a newly established species within the plant pathogenic family Pectobacteriaceae. Bacteria belonging to this species are causative agents of diseases in economically important crops (e.g. potato) in a wide range of different environmental conditions, encountered in Europe, North America, Africa, and New Zealand. Severe disease symptoms result from the activity of P. parmentieri virulence factors, such as plant cell wall degrading enzymes. Interestingly, we observe significant phenotypic differences among P. parmentieri isolates regarding virulence factors production and the abilities to macerate plants. To establish the possible genomic basis of these differences, we sequenced 12 genomes of P. parmentieri strains (10 isolated in Poland, 2 in Belgium) with the combined use of Illumina and PacBio approaches. De novo genome assembly was performed with the use of SPAdes software, while annotation was conducted by NCBI Prokaryotic Genome Annotation Pipeline. Results The pan-genome study was performed on 15 genomes (12 de novo assembled and three reference strains: P. parmentieri CFBP 8475T, P. parmentieri SCC3193, P. parmentieri WPP163). The pan-genome includes 3706 core genes, a high number of accessory (1468) genes, and numerous unique (1847) genes. We identified the presence of well-known genes encoding virulence factors in the core genome fraction, but some of them were located in the dispensable genome. A significant fraction of horizontally transferred genes, virulence-related gene duplications, as well as different CRISPR arrays were found, which can explain the observed phenotypic differences. Finally, we found also, for the first time, the presence of a plasmid in one of the tested P. parmentieri strains isolated in Poland. Conclusions We can hypothesize that a large number of the genes in the dispensable genome and significant genomic variation among P. parmentieri strains could be the basis of the potential wide host range and widespread diffusion of P. parmentieri. The obtained data on the structure and gene content of P. parmentieri strains enabled us to speculate on the importance of high genomic plasticity for P. parmentieri adaptation to different environments

Isolation, detection and characterization of Pectobacterium and Dickeya species

This chapter outlines isolation, detection and characterization methods for soft rot Pectobacteriaceae (SRP) and finishes with recommendations for diagnostics of SRP and perspectives for improved detection using metagenomic and pan-genomic approaches. For dilution plating and isolation of SRP, crystal violet pectate is still the medium of preference, although it is poorly selective. To improve the diagnostic sensitivity of detection methods, enrichment methods are used in which selective growth of the pathogen is enhanced by incubation in a pectate broth under low oxygen conditions. For molecular characterization, various finger printing techniques are described, but today analysis based on phylogenetic markers are preferred, in particular multi-locus sequence typing of housekeeping genes and comparative genetics using whole-genome sequences. For phenotypic characterization, methods are used based on serological, biochemical and physiological features. Currently the most precise phenotyping method is protein mass fingerprinting using a MALDI-TOF Mass Spectrometry. For detection of the pathogen, DNA-based amplification methods are generally used, including conventional PCR, real time (TaqMan) PCR assays and LAMP assays. They can detect the pathogen at a low density and allow recognition of the pathogens at different taxonomic levels. An inventory has been included of recently developed primer and probe combinations

Diseases Caused by Pectobacterium and Dickeya Species Around the World

202

Pectobacterium and Dickeya: Environment to Disease Development

The soft rot Pectobacteriaceae (SRP) infect a wide range of plants worldwide and cause economic damage to crops and ornamentals but can also colonize other plants as part of their natural life cycle. They are found in a variety of environmental niches, including water, soil and insects, where they may spread to susceptible plants and cause disease. In this chapter, we look in detail at the plants colonized and infected by these pathogens and at the diseases and symptoms they cause. We also focus on where in the environment these organisms are found and their ability to survive and thrive there. Finally, we present evidence that SRP may assist the colonization of human enteric pathogens on plants, potentially implicating them in aspects of human/animal as well as plant health