Isolation and Characterization of Rhizosphere Bacillus thuringiensis Isolates Showing Antifungal Activity

P. Auger, J-M. Juteau, M. Sirois

Author address: 

Univ. Quebec Trois-Rivieres, Trois-Rivieres, QC, CANADA.


Non GMO microorganisms offer an attractive alternative to currently used pest control practice, as chemical pesticides are raising concerns about human health and environmental quality. For example, B. thuringiensis (Bt) have been used extensively as an insecticide, but few reports exist concerning other Bt properties. To broader the use and exploit its different roles in agriculture, we aimed at the isolation of natural Bt strains that display activities against important phytopathogenic fungi. To recover Bt strains from rhizosphere soil samples, 1g of soil was suspended in PBS-buffer and the sample was incubated at 65 °C for 20 minutes. Aliquots were spread on Cereus Selective Agar and incubated at 30°C for 3 days to select for "œcereus group" isolates. Potential isolates were streak-purified on Brilliance Bacillus cereus agar to complete the screening. Distinctive Bt isolates were examined microscopically for the presence of crystal inclusions. The antifungal activity (growth inhibition zone) of all identified Bt isolates was tested on Sabouraud-dextrose agar plates against growth of Botrytis cinerea, Fusarium oxysporum, and Pythium sp. Results were compared with various control strains (positive: B. subtilis GB03 and QST173 and negative: B. subtilis 168). More than 50 putative Bt isolates were screened for in vitro antifungal activity. Most of the Bt isolates did not produce inhibition zone for any of the different fungi. Some Bt isolates (14) showed antifungal activity for 1 of the group while 2 particular Bt isolates showed strong activity (large inhibition zone) against the 3 fungi tested. These data confirmed the existence of different biocontrol modes of action within some Bt strains. We found natural Bt strains isolated from various rhizosphere soil exhibiting significative antifungal activity. Specific insecticidal activity characterization of the most interesting isolates is currently underway. In addition of their well-known insecticide action, some Bt strains could be exploited for additional properties such as their antifungal action and act as polyvalent biocontrol agent, which would be an innovative approach.

abstract No: 


Full conference title: 

110th General Meeting American Society for Microbiology
    • ASM 110th (2010)