Abstract:

To explore the mechanisms of pine wilt disease, in vitro toxin production of a bacterium strain, GcM5-1A (Pseudomonas fluorescens) isolated and identified from Busaphelenchus xylophelus, was examined. Toxicity of the cell free filtrate of the liquid medium after culturing the bacterium was assayed by the fluorescence microscopic bioassay. Results of the bioassay showed that toxicity of the cell free filtrate of the liquid medium was increased with culturing days. Toxicity of the cell free filtrate reached a relatively stable phase from the 4^th day during a 7-day experiment. Therefore, 4 days can be the duration of the culturing time, when the toxins of the strain are going to be isolated and identified. The cell free filtrate of the liquid medium after 4 days' culturing was dialysed with DM-36 dialysed into two parts, the interior part of the dialayser and the exterior part. Bioassay results indicated that toxicity was existed in both the interior and the exterior parts, because there was significant differences between the interior, the exterior parts and the control respectively in the toxicity of their cell free filtrates by t_test. The result demonstrated that a single compound did not cause toxicity of GcM5-1 strain, rather than multi-components, in which there were both macro-molecules, like proteins, peptides, enzymes, and small organic molecules.

Key words: toxin, Pseudomonas fluorescens, Busaphelenchus xylophelus, dialaysis, fluorescence microscopic bioassay