Five lysogenic strains in
Pseudomonas mori, the pathogen of bacterial blight of mulberry, were detected by plating and other methods. Each temperate phage isolated from these lysogenic strains was named as φ5, φ6, φ7b, φ7c and φM5, and their properties were investigated.
Both φ7b and φ7c showed a broader host range and were spontaneously produced to attain higher concentrations (10
6 to 10
7/ml) as compared to others from each parent bacterial strain after shaking culture for 24 hours at 28C. Plating efficiency was markedly influenced by the bacterial strain used as indicator.
All the phage isolates formed plaques at the temperature range of 5 to 28C. Three isolates, φ7b, φ7c and φ5, formed small round and turbid plaques of about 0.5mm in diameter at 20C of optimum growth temperature, while others formed medium-sized round and comparatively clear plaques of 1 to 2mm in diameter.
Both φ7b and φ7c were extreamely heat stable, showing thermal inactivation point of 95C for 10min., and sensitive to chloroform, while other isolates were inactivated at about 50C and resistant to chloroform.
From the foregoing properties, these phage isolates were classified into three groups, A, B and C, respectively including φ6 and φM5, φ5, andφ7b and φ7c.
Each lysogenic strain did not lose its lysogeny even by 15 times repeated single colony isolation or passing mulberry leaves. The lysogeny was also independent from colony type mutation from smooth to rough. Several mutants appeared to be defective lysogenic strain were obtained during the course of this experiment.
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