Antibiotics produced by Micromonospora carbonacea against Xanthomonas oryzae pv. oryzicola

Abstract:

[Background] Xanthomonas oryzae pv. oryzicola is a pathogen to cause rice bacterial leaf streak. Micromonospora carbonacea JXNU-1 with broad-spectrum antibacterial activities was isolated from soil previously, and its fermentation products (designated as “antibiotic JX”) show strong antibacterial activity against plant pathogenic bacteria. [Objective] The antibacterial activity of antibiotic JX against Xanthomonas oryzae pv. oryzicola and its mechanism were studied. [Methods] The size of the inhibition zone was measured with cylinder plate method, and the determination of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was performed by serial tube double dilution. Additionally, the mechanism was elaborated through the investigations of cell morphology, electrical conductivity of bacterial suspension, macromolecule leakage, biosynthesis level of protein and nucleic acid and bacterial membrane potential. [Results] The average diameter of inhibition zones was 18.84±0.28 mm. The MIC and MBC was 1.39 μg/mL and 2.78 μg/mL, respectively. Complete sterilization was achieved within 12 hours, indicating a fast sterilization of antibiotic JX. In the presence of antibiotic JX, an obvious change was observed for the cell morphology of Xanthomonas oryzae pv. oryzicola. Moreover, the conductivity and macromolecule leakage of bacterial suspension as well as bacterial membrane potential increased with antibiotic concentration, but the protein content decreased. The down-regulated ef-p expression was detected by real-time fluorescence quantitative PCR. [Conclusion] The antibiotic JX exhibits a strong antibacterial ability against Xanthomonas oryzae pv. oryzicola by means of disturbing the integrity of bacterial membranes and inhibiting biosynthesis of proteins.