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Microbiology 148 (2002), 4015-4024
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Microbiology (2002), 148, 4015-4024.
© 2002 Society for General Microbiology

Research Paper

Genetics of biosynthesis and structure of the capsular exopolysaccharide from the Asian pear pathogen Erwinia pyrifoliae

Won-Sik Kim1, Martin Schollmeyer1, Manfred Nimtz2, Victor Wray2 and Klaus Geider1

Max-Planck-Institut für Zellbiologie, Rosenhof, 68526 Ladenburg, Germany1
GBF, Gesellschaft für Biotechnologische Forschung mbH, Mascheroder Weg 1, 38124 Braunschweig, Germany2

Author for correspondence: Klaus Geider. Tel: +49 6203 106 117. Fax: +49 6203 106 122. e-mail: kgeider{at}zellbio.mpg.de

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 1H-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.

Keywords: Asian pear blight, fire blight, amylovoran, sugar linkage, cps genes

Abbreviations: CPC, cetylpyridinium chloride; EPS, exopolysaccharide; HR, hypersensitive reaction

The GenBank accession number for the sequence reported in this paper is AJ300463.






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