Identification of a nonpathogenic Erwinia amylovora guaB mutant

Abstract

A nonpathogenic Erwinia amylovora transposon mutant that has an insertion in the guaB gene was isolated. The mutation results in a nutritional requirement for guanine or xanthine, and loss of ability to produce ooze on immature pear fruit and to cause symptoms in the apple seedling assay. The mutant expressed other known virulence determinants including extracellular polysaccharide and had an intact hrp/dsp cluster. In addition it was able to grow in host tissue, although the population size in planta was maintained at a considerably lower level than that seen with the parent strain. The inability of the Erwinia amylovora guaB mutant to cause disease indicates that levels of guanine in plant tissue are likely to be insufficient to maintain optimal growth via the purine salvage pathway. This, in turn, appears to compromise the ability of the mutant to develop a sufficiently large population size in planta to overcome host defence mechanisms and cause disease symptoms. This indicates that a functional de novo guanine synthetic pathway is important for Erwinia amylovora to grow on plant tissue and cause disease.

Luteoforol, a flavan 4-ol, is induced in pome fruits by prohexadione-calciumand shows phytoalexin-like properties against Erwinia amylovoraand other plant pathogens

“…For the inhibition test on solid medium, plates with M9 minimal medium (Sambrook et al, 1989) were prepared and overlaid with a thin layer (2-3 mm) of minimal medium containing 10 7 cfu ml )1 of the different bacteria. Minimal medium M9 was chosen to mimic the lack of nutrients in the plant apoplast (Eastgate et al, 1997). Sterile disks of filter paper (5 mm diam.…”

Erwinia amylovora pyrC mutant causes fire blight despite pyrimidine auxotrophy

“…amylovora cannot obtain sufficient guanine from the host during infection (Eastgate et al . ). However, our understanding of Erw.…”

“…amylovora guanine auxotroph mutant was nonpathogenic on apple seedlings and immature pear fruits, indicating Erw. amylovora cannot obtain sufficient guanine from the host during infection (Eastgate et al 1997). However, our understanding of Erw.…”

Erwinia amylovora: the molecular basis of fireblight disease

“…, 1994). Levels of other metabolic precursors may also be low enough to compromise bacterial growth, for example an E. amylovora guanine biosynthetic mutant has been shown to be nonpathogenic (Eastgate et al. , 1997).…”

“…In addition, galactose is proposed to be limiting in plant tissue, necessitating the conversion of UDP-glucose to UDP-galactose for amylovoran biosynthesis (Metzger et al , 1994). Levels of other metabolic precursors may also be low enough to compromise bacterial growth, for example an E. amylovora MOLECULAR PLANT PATHOLOGY (2000) 1 (6), 325-329 © 2000 BLACKWELL SCIENCE LTD guanine biosynthetic mutant has been shown to be nonpathogenic (Eastgate et al , 1997).…”