Characteristics and antimicrobial activity of Bacillus subtilis strains isolated from soil

Antagonistic Bacillus strains were isolated from soil and analyzed for the purpose of determining whether they could be used as natural biological agents. Primary in vitro screening for antagonism of the isolates was performed against five phytopathogenic mould fungi. Strains TS 01 and ZR 02 exhibited the most pronounced inhibitory effects. They were identified as Bacillus subtilis on the basis of their morphological, cultural and physiology-biochemical properties as well as their hierarchical cluster analysis conducted by means of computer program SPSS. The antimicrobial activity of the strains from cultural medium and sterile filtrate were determined in vitro against a great number of predominantly phytopathogenic fungi and bacteria. TS 01 and ZR 02 strains exhibited very broad and at the same time degree varying antibiotic spectra of activities against both Gram-positive and Gram-negative microorganisms. Many of them were tested against sensitivity to the antimicrobial action of B. subtilis for the very first time. B. subtilis TS 01 and ZR 02 showed highest antifungal activity (sterile zone in diameter over 37 mm) against Alternaria solani, Botrytis cinerea, Monilia linhartiana 869, Phytophthora cryptogea 759/1 and Rhizoctonia sp. The most sensitive bacterial species were found to be Pseudomonas syringae pv. tomato Ro and Xanthomonas campestris with sterile zones 48.0 and 50.0 mm in diameter, respectively. The latter draws a conclusion that the isolated and identified Bacillus subtilis strains are promising natural biocontrol agents and should be further studied and tested for control of numerous plant diseases.