VIEW ARTICLE

Molecular Plant Pathology

Association of Bacteriophage Particles with Toxin Production by Clavibacter toxicus, the Causal Agent of Annual Ryegrass Toxicity. Kathy M. Ophel, Dept. of Crop Protection, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia 5064, Present address: Cooperative Research Centre for Soil and Land Management, CSIRO Division of Soils, Glen Osmond, South Australia 5064; Alan F. Bird(2), and Allen Kerr(3). (2)CSIRO Division of Soils, Glen Osmond, South Australia 5064; (3)Dept. of Crop Protection, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia 5064. Phytopathology 83:676-681. Accepted for publication 17 February 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-676.

The association between Clavibacter toxicus, the causal agent of annual ryegrass toxicity in Australia, and a bacteriophage specific to the bacterium was examined. Wild-type C. toxicus strains (designated type 1) did not produce corynetoxin, the toxin responsible for annual ryegrass toxicity. When bacteria were infected with the bacteriophage, two types of colonies resulted. One type (type 2) produced toxin and the other (type 3) did not. Antiserum was raised to purified bacteriophage particles. Type 2 bacteria reacted positively to the antiserum in enzyme-linked immunosorbent assay (ELISA) but type 1 and 3 colonies did not. Culture of toxin-producing (type 2) bacteria with antiphage antiserum restored normal colony morphology and eliminated activity in the corynetoxin bioassay. DNA hybridization revealed that bacteriophage DNA was not present in type 1 strains but was present in type 2 and 3 strains. Bacteriophage DNA was not integrated into bacterial DNA and was present in high copy number. Toxin-producing strains had an unusual morphology, and when examined by electron microscopy, the bacterial capsule and cell membrane appeared disrupted. Intact phage particles were visible in transmission electron micrographs of the infected bacteria. Evidence indicated that bacteriophage in toxin-producing bacteria (type 2 colonies) was in a phage-carrier state with C. toxicus, and bacteriophage presence was correlated with production of corynetoxin.