Isolation and evaluation of copper- and bactericide-resistant mutants of putative biocontrol agents of soft rot of Chinese cabbage [Brassica chinensis]
1999
Kyeremeh, A.G. (Tohoku Univ., Sendai (Japan). Inst. of Genetic Ecology) | Kikumoto, T. | Chuang, D.Y. | Gunji, Y. | Takahara, Y.
A modified Bacto potato-dextrose agar (PDA) was prepared by incorporating bromothymolblue (BTB), crystal violet and lactose into PDA. This medium was used as a selective and diagnostic medium for isolating copper- and bactericide-resistant mutants of putative biocontrol agents of the soft-rot bacterium, Erwinia carotovora subsp. carotovora. Putative mutants resistant to between 3.75-6.26 mM (600-1000 mug/ml) copper sulfate were isolated through three sequential isolations on this medium. The copper resistance of this bacterium increased gradually following each isolation. However, these mutants were found to be susceptible to copper-based bactericides like copper (II) hydroxide, dithianon-copper chloride basic and organic copper. Moreover, a decrease in the copper resistance of the mutants, especially those of strain 2T-2 was observed after a period of storage but no change in their bacteriocin activity was observed. Using these mutants as parents, spontaneous mutants resistant to 250- and 500-times dilution of organic copper and copper sulfate basic on PDA, respectively, were isolated. One of these mutants designated as 2TQ-rif-4 survived in 600- and 1200-times diluted solutions of organic copper for at least 3 and 6 hr, respectively. As much as 10(6) cfu/ml of this mutant survived in the solution of organic copper for 24 hr at a dilution rate of 1800-times
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