Antimicrobial activity of isolate HL-12 against Clavibacter michiganensis subsp. michiganensis in the presence of cadmium

An actinomycete, strain HL-12, that was isolated from a farmland on the Huajiachi campus of Zhejiang University was capable of inhibiting the growth of Clavibacter michiganensis subsp. michiganensis (Cmm) and was identified as a member of Streptomyces. Its antimicrobial activity against Cmm was measured using the agar plate sensitivity method in pure culture and evaluated by the inhibition ratio of Cmm in soil. The inhibitory activity of strain HL-12 against Cmm following exposure to low concentrations of Cd was greater than the inhibitory activity following exposure to high concentrations of Cd both in liquid culture and in soil. A stronger inhibition was also seen following a 24 h preculture in the presence of Cd in liquid culture. The growth of Cmm in soil was stimulated at low concentrations of Cd (<5.0 mg Cd kg⁻¹ dry soil) but inhibited when cultured in high concentrations of Cd (5.0 and 10.0 mg Cd kg⁻¹ dry soil). A higher inhibition ratio of strain HL-12 against Cmm, which was over 40% after soil incubation for 2 weeks, was observed following exposure to low concentrations of Cd (<5.0 mg Cd kg⁻¹ dry soil).