Antibiosis by Bacillus amyloliquefaciens ribonuclease barnase expressed in Escherichia coli against symbiotic and endophytic nitrogen-fixing bacteria

A modified antibiosis assay was used to evaluate growth inhibition of symbiotic and endophytic bacteria by E. coli strains producing Bacillus amyloliquefaciens ribonuclease, barnase. Inhibition zones were only observed when the assays were performed in minimal medium agar. However, bacterial growth inhibition was not detected when using rich medium or susceptible strains expressing the ribonuclease inhibitor protein, barstar. Our results suggest that barnase may act as a broad range bacteriocin. The ecological significance of these results is discussed.