Screening and Characterization of Potential PGPR/Bacillus sp. Strains Isolated From Various Rhizospheres

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


Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots, promote plant growth and confers protection against various phytopathogens. PGPR have been identified within various bacterial groups. However, many commercially developed PGPR belong to endospore-forming species Bacillus or Paenibacillus, which confer stability for formulation and storage. In order to develop new Bacillus sp. for both i) biocontrol of phytopathogens and ii) growth-promotion, we aimed to isolate and characterize endospore-forming bacterial isolates that could be potentially useful as inoculants in various agricultural crops. One hundred rhizosphere soil samples were resuspended in PBS buffer and heated at 70C for 30 minutes. Aliquots were plated on Cereus Selective Agar and selected colonies were streak-purified on R2A agar plates. In the first step, isolates that showed antagonist activity against phytopathogenic fungi Fusarium oxysporumRhizoctonia solani and Botrytis cinereawere selected and tested for production of phytohormones (auxins, indole acetic acid-IAA), phosphate solubilization , and their ability to fix atmospheric nitrogen. Among the antifungal strains, a total of 34 isolates were positive for at least one of the above characteristics. IAA positive isolates showed root-growth stimulation when tested in vitro with Arabidopsis thaliana seeds. Preliminary data from sequencing results (16S gene) and basic biochemical tests showed that most of the isolated strains corresponded to the Bacillus subtilis-amyloliquefaciens group (non-pathogen), which is in conformity with bio-security issues. Based on sequencing of the nifH gene, diazotrophic isolates were found to belonged exclusively to Paenibacillus species. This study pointed out several Bacillus sp.strains showing PGPR attributes and analysis of supplementary PGPR characteristics may lead to the selection of new performant and useful inoculants to be used in various food crops, potentially reducing the use of chemical fertilizers.

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American Society for Microbiology General Meeting
    • ASM 113th (2013)