1.E.58. The Erwinia Phage Phi-Ea1h Holin (EPPE-Hol) Family
A 3.3-kb fragment of genomic DNA from bacteriophage Phi-Ea1h encoding an amylovoran-directed depolymerase/lyase was sequenced, and three open reading frames (ORFs) were identified. The first ORF encoded a lysozyme; the second encoded a holin that may form a pore supporting cell lysis by the lysozyme, and the third encoded a protein of 657 amino acids which when deleteted abolished extracellular polysaccharide (EPS)-degrading activity (Kim and Geider 2000). A putative promoter and a ribosome binding sequence were located in front of the gene. The enzyme degraded the EPS-capsules of Erwina amylovora. In virulence assays, no symptoms were detected for a low inoculum of an E. amylovora strain when pear slices were soaked in a solution of depolymerase in contrast to control slices without addition of the enzyme. Furthermore, gfp- or lux-labeled E. amylovora cells were not propagated when their amylovoran capsules were removed by the depolymerase. The enzyme could be useful for biological control of fire blight. Since no signal sequence was observed at the N-terminus of the enzyme, it is possible that the holin faciliates the export of the enzyme as well as the lysozyme (Kim and Geider 2000).