Phylogeny and Virulence of Naturally Occurring Type III Secretion System-Deficient Pectobacterium Strains

Abstract

Pectobacterium species are enterobacterial plant-pathogenic bacteria that cause soft rot disease in diverse plant species. Previous epidemiological studies of Pectobacterium species have suffered from an inability to identify most isolates to the species or subspecies level. We used three previously described DNA-based methods, 16S-23S intergenic transcribed spacer PCR-restriction fragment length polymorphism analysis, multilocus sequence analysis (MLSA), and pulsed-field gel electrophoresis, to examine isolates from diseased stems and tubers and found that MLSA provided the most reliable classification of isolates. We found that strains belonging to at least two Pectobacterium clades were present in each field examined, although representatives of only three of five Pectobacterium clades were isolated. Hypersensitive response and DNA hybridization assays revealed that strains of both Pectobacterium carotovorum and Pectobacterium wasabiae lack a type III secretion system (T3SS). Two of the T3SS-deficient strains assayed lack genes adjacent to the T3SS gene cluster, suggesting that multiple deletions occurred in Pectobacterium strains in this locus, and all strains appear to have only six rRNA operons instead of the seven operons typically found in Pectobacterium strains. The virulence of most of the T3SS-deficient strains was similar to that of T3SS-encoding strains in stems and tubers.The genus Pectobacterium (formerly Erwinia) contains both narrow-and broad-host-range bacterial plant pathogens that cause soft rot, stem rot, wilt, and blackleg in species belonging to over 35% of plant orders (20). Four Pectobacterium species have been described: Pectobacterium atrosepticum, Pectobacterium betavasculorum, Pectobacterium carotovorum, and Pectobacterium wasabiae (9). The recently described organism P. carotovorum subsp. brasiliensis is genetically distinct from previously described Pectobacterium taxa; approximately 82% of its genes are shared with P. atrosepticum, and 84% of its genes are shared with P. carotovorum subsp. carotovorum, while 13% of its genes are found in neither P. atrosepticum nor P. carotovorum subsp. carotovorum (7,10,20). To date, only P. carotovorum subsp. carotovorum and P. atrosepticum have been reported to occur in the same field (14, 21). P. carotovorum subsp. carotovorum is found worldwide, and P. atrosepticum is found in cool climates; while P. carotovorum subsp. brasiliensis has been found only in Brazil, Israel, and the United States, it is likely to have a wider distribution (20). Compared to the ecology and genetics of P. carotovorum subsp. carotovorum and P. atrosepticum, little is known about the ecology and genetics of P. betavasculorum, P. wasabiae, or P. carotovorum subsp. brasiliensis.Pectobacterium strains isolated from potato are diverse based on serology, genome structure, and fatty acid composition (5, 35). Previous epidemiological studies of pectolytic Enterobacteriaceae were complicated by the diversity of this group and the lack of tools capable of placing all isolates ...

Pectobacterium carotovorum subsp. carotovorum - the causal agent of broccoli soft rot in Serbia

“…Previously, P. c. ssp. carotovorum strains had been shown to vary in their ability to cause HR in tobacco and the presence of type III secretion system (Yap et al, 2004;Kim et al, 2009;Baghaee-Ravari et al, 2011;Nabhan et al, 2012).…”

The Role of Secretion Systems and Small Molecules in Soft-Rot Enterobacteriaceae Pathogenicity

“…Similarly, an orchid-infecting species, Pectobacterium cypripedii, previously included within Pectobacterium, was recently transferred to the related genus Pantoea (13). Both Dickeya and Pectobacterium encompass diverse taxa (76,96), and multiple SRE taxa may be present in a field or even an individual plant (76,147,162), which adds complexity to understanding how soft-rot disease progresses under natural conditions.…”

“…Strains from both Pectobacterium and Dickeya lacking a T3SS have been isolated, suggesting that the T3SS is not required for survival (76,126). Pectobacterium strains naturally lacking a T3SS are not virulent on leaves, although they can macerate potato stems and tubers.…”

Characterization of Pectobacterium carotovorum subsp. odoriferum causing soft rot of stored vegetables

“…The identification of P. c. subsp. odoriferum has also been based on the recA gene (Waleron et al 2002a), the rpoS gene (Waleron et al 2002b), amplified fragment length polymorphism (AFLP) (Nabhan et al 2012a), and multilocus sequence analysis (MLSA) (Ma et al 2007;Kim et al 2009;Nabhan et al 2012b).…”