Antimicrobial activity of Streptomyces spp. isolated from bean rhizospheric soil against Xanthomonas sp.

Species of the genus Streptomyces are a promising strategy for bacterial disease management in agriculture crops. The present study aimed to isolate and identify Streptomyces-like actinobacteria from rhizospheric soil using physical pretreatments and to evaluate their antimicrobial activity against Xanthomonas sp. A rhizospheric soil from a bean plantation was pretreated using dry heat or microwave radiation for isolating actinobacteria. Antimicrobial activity was evaluated using the double agar layer method; 73 isolates exhibiting Streptomyces colony characteristics were obtained from the soil after dry heat pre-treatment series (50 BVBZ) and microwaves (23 BVBZMW); 34 BVBZ (68%) isolates inhibited Xanthomonas sp. growth with 11.2-35.8mm halos in diameter. Fifteen (15) of 23 BVBZMW isolates (65%) recorded inhibition zones ranging from 15.7 to 73.6mm in diameter. The 16S rRNA gene sequence analysis confirmed three isolates with greater antimicrobial activity belonging to the genus Streptomyces. Streptomyces sp. BVBZ 35, BVBZ 47, and BVBZMW 18 shared greater 16S rRNA gene sequence identity with S. monomycini NRRL B-2409^T (100%), S. nogalater JCM 4799^T (99.38%) and S. leeuwenhoekii C34^T (99.45%), respectively. Streptomyces sp. BVBZMW 18, which exhibited the highest antimicrobial activity, could only be cultured after microwave irradiation of the soil. Streptomyces species isolated from rhizospheric soil using physical pretreatments are a potentially novel antimicrobial source for Xanthomonas disease control.