ABSTRACT
A spontaneous streptomycin-resistant mutant, Bacillus subtilis NB22-1, which was obtained from NB22, was used. The growth rate and iturin productivity of NB22-l were similar to those of the parental strain NB22. Soil samples were prepared in triplicate for each experiment. In each cfu determination for total cell number and spore number, at least three different dilutions were spread in duplicate onto the selective plates, and an average value was calculated. A rapid death rate and extinction of vegetative cells of the transformants was observed in soil. This was due to the poorer survival of the transformants in soil or less active sporulation or a higher susceptibility to starvation than the host cells. Many bacteria have been found to suppress plant diseases caused by soilborne pathogens, with most of their disease-suppressing ability being attributed to the production of antimicrobial metabolites. Genes coding for the biosynthesis and regulation of some of these metabolites have been cloned.
