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Bacillus subtilis S44 is a promising plant growth-promoting rhizobacterium
and a potent biocontrol agent isolated from cotton rhizosphere. The ituD
gene was cloned and identified from S44. A suicide vector containing ituD
gene from B. subtilis S44 was recombined into the B. subtilis
S44 chromosome to disrupt the ituD gene. Recombination was demonstrated
by PCR, antifungal activity and HPLC confirmed the loss of the ituD gene.
The growth rate of the recombinant is severely depressed compared with wild
type and tetracycline had no effect on the growth rate the mutant strains. Antifungal
activity in cell-free extracts of the recombinant has almost no antifungal activity
compared with the wild strain. HPLC analysis show that the wild strian produce
iturin A at an amount of 89.4 μg mL-1 while the ituD
mutant only 3.41 μg mL-1. In pot and plot tests, the control
effects of S44 treatment were 80.30 and 72.97%, respectively. The mutant strains
S1 and S2 exhibit no control effect of cotton Rhizoctoniosis. These results
suggest that the ituD gene was important for iturin A synthesis and
biocontrol activity of S44.
