Genetics of biosynthesis and structure of the capsular exopolysaccharide from the Asian pear pathogen Erwinia pyrifoliae The GenBank accession number for the sequence reported in this paper is AJ300463.

Abstract

Erwinia pyrifoliae is a novel bacterial pathogen, which causes Asian pear blight and is related to Erwinia amylovora, the causative agent of fire blight. E. pyrifoliae produces exopolysaccharide (EPS) related to amylovoran in its sugar composition and sugar linkages. This was shown by degradation of the EPS with a viral depolymerase, and by methylation analysis and ESI/MS. The structure of the repeating units was confirmed by 1 H-NMR spectra. The EPS of E. pyrifoliae carried side chains, which were mainly terminated by acetyl and pyruvyl residues as found previously for amylovoran. On the other hand, a second side chain with glucose found for up to 65 % of the repeating units of amylovoran was completely absent. The nucleotide sequences of five genes of the cps cluster of E. pyrifoliae encoding proteins for EPS synthesis were characterized and displayed a high homology with the corresponding ams genes. Similar functions of the gene products are assumed. As for ams mutants of E. amylovora, a cpsB mutant of E. pyrifoliae did not synthesize EPS and did not produce ooze on slices of immature pears or symptoms on pear seedlings. The cps mutant was complemented for EPS synthesis and virulence on pear slices with a gene cluster of E. amylovora that included amsB.

Genomics and current genetic understanding of Erwinia amylovora and the fire blight antagonist Pantoea vagans

“…4) resulting potentially in the production of amylovoran. Amylovoran biosynthesis is a specific virulence factor in E. amylovora and E. pyrifoliae reflected in the fact that deletion or mutagenesis of specific genes renders the pathogens avirulent (Bellemann and Geider 1992;Kim et al 2002). The exopolysaccharide gene clusters, producing CPS of the two non-amylovoran producing species and also of Pantoea spp., might represent the ancestral state.…”

Molecular Characterization of Natural Erwinia pyrifoliae Strains Deficient in Hypersensitive Response

“…The properties of the 13 isolated defective E. pyrifoliae strains showed a correlation of virulence on pears and HR on tobacco (Table 1). An EPS-deficient mutant of E. pyrifoliae had previously been complemented with ams genes of E. amylovora (12). In a similar approach, we attempted to complement the HR-deficient strain Ep2/97 with hrp genes of E. amylovora.…”

“…The pathogenicity of E. amylovora depends on both the synthesis of the acidic exopolysaccharide (EPS) amylovoran (2,17) and a functional type III secretion system, involved in induction of a hypersensitive response (HR) (1,5,9,17). The pear pathogen E. pyrifoliae shares substantial homologies to ams genes and also requires capsular EPS for pathogenicity (12).…”

Erwinia spp. from pome fruit trees: similarities and differences among pathogenic and non-pathogenic species

“…Pyrifolan is an EPS (Geider 2000) that has the same sugar composition in the repeating units as amylovoran and presents identical linkages (except the lack of a second side chain of glucose), but some authors think that the high degree of similarity of the chemical structures of both EPSs may not justify the name of pyrifolan by analogy to amylovoran (Kim et al 2002).…”