炭样小单孢菌产抗生素对水稻细菌性条斑病菌的抗菌作用及其机理

Antibiotics produced by Micromonospora carbonacea against Xanthomonas oryzae pv. oryzicola

【背景】水稻细菌性条斑病菌为水稻细菌性条斑病的病原菌,土壤中分离到的一株具有广谱抗菌活性的炭样小单孢菌JXNU-1,其发酵产物(即抗生素JX)对植物病原菌具有较强的抑菌活性。【目的】研究抗生素JX对水稻细菌性条斑病菌的抗菌作用及其机理。【方法】采用杯碟法测定抑菌圈大小,二倍稀释法测定最低抑菌浓度、最低杀菌浓度,并且从菌体形态观察、电导率变化、培养液大分子漏出、蛋白质合成、核酸合成和膜电位变化6个方面探究其作用机理。【结果】抗生素JX对水稻细菌性条斑病菌的抑菌圈直径达18.84±0.28mm,最低抑菌浓度和最低杀菌浓度分别为1.39μg/m L和2.78μg/mL,且杀菌速度很快,作用12 h的杀菌率达100%。在抗生素JX作用下,水稻细菌性条斑病菌的细胞形态发生改变,培养液电导率、膜电位和大分子漏出量均随抗生素浓度增加而增大,但菌体蛋白质含量随着抗生素浓度增加而降低,同时,通过实时荧光定量PCR方法检测发现ef-p表达量下调。【结论】抗生素JX对水稻细菌性条斑病菌具有较强的抗菌作用,推测其抑菌机理是通过抑制菌体蛋白质的生物合成和影响细胞膜完整性而起作用。

[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 was18.84±0.28 mm.The MIC and MBC was 1.39μg/mL and 2.78μg/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.