Erwinia amylovora secretes DspE, a pathogenicity factor and functional AvrE homolog, through the Hrp (type III secretion) pathway

Abstract

Erwinia amylovora was shown to secrete DspE, a pathogenicity factor of 198 kDa and a functional homolog of AvrE of Pseudomonas syringae pv. tomato. DspE was identified among the supernatant proteins isolated from cultures grown in an hrp gene-inducing minimal medium by immunodetection with a DspE-specific antiserum. Secretion required an intact Hrp pathway.

FIG. 1

Immunodetection of DspE in a Western blot of culture supernatant and cell fractions. Cultures of the Erwinia amylovora Hrp pathway mutant strain Ea273-K178 (lanes 1), the wild-type strain Ea273 (lanes 2), and a partial dspE deletion mutant strain, Ea273dspEΔ1521 (lanes 3), were grown under hrp gene-inducing conditions. Molecular weight markers (BenchMark prestained protein ladder; Life Technologies, Gaithersburg, Md.) are indicated. Migration of proteins from the culture supernatant was slightly retarded due to the presence of the extracellular polysaccharide of Erwinia amylovora.