Mutation Of CpxRA Gene In Xenorhabdus Bovienii YL002and Study On Antimicrobial Activity

Xenorhabdus as a kind of important biological control resource shows different degreeson inhibitory activity of pathogens，therefore, extensive researches of its application werecarried out in all over the world. This experiment was carried out in vitro and in vivo usingBotrytis cinerea and Phytophthora capsici as research objects. Protective and therapeuticeffects of Xenorhabdus bovienii YL002fermentation broth were studied and applicationprospect on agriculture disease control was discussed. Gene cpxRA of YL002was recombinedby molecular biology methods and expected to mutate，so mutant strain with high antibioticscontents can be gained. Through research，results were as follows：1. Metabolites of X. bovienii YL002exhibited higher antimicrobial activity to manyplant pathoges. The inhibition rate of the cell-free filtrate against B. cinerea, P. capsici andSclerotinia sclerotiorum were over90%, respectively and over80%on Exserohilum turcicumand Penicillium digitatum.2. The antimicrobial activity of X. bovienii YL002was tested for its ability to inhibitmycelia growth and spore germination of plant pathogenic fungi and oomycete, in vitro. The10%cell-free filtrate exhibited higher inhibition effects on mycelia growth of P. capsici(100%) and B. cinerea (95.42%). Also, it showed some effects in germination of sporangia.According to experiments，toxicology equation of the cell-free filtrate of the stain ongermination of sporangia of P. capsici and B. cinerea were y=5.6805+1.2544x andy=6.1407+2.7887x. The50%inhibition concentration (EC50) of the cell-free filtrate against P.capsici and B. cinerea were286.8ml/L and389.9ml/L, respectively. The results of B. cinereaexperiment were as follows, control of the mycelium was tender, slim, plump and stretch,treatment group deformed hyphae, atrophy and rupture, and a large number of sporulation,sporulation rate was faster than the control; pathogen Phytophthora capsici activityexperiments showed, the control of the mycelium thin, smooth, long knot space, lessbifurcation, produce more spores, while the treatment group performed serious myceliumdeformation, fracture, knot spacing was very short, bifurcation was very short, almost did notproduce spores. 3. Further, In vivo potent antimicrobial activity of X.bovienii YL002was demonstratedon tomato fruits infected with the pathogen B. cinerea and pepper plants infected with P.capsici, respectively. The cell-free filtrate showed the therapeutic effect of56.0%andprotective effect of66.3%against B. cinerea of tomato fruits compared with the control. Thecell-free filtrate also showed potent effect against P. capsici, with a therapeutic effect of70.6%and a protective effect of60.15%on pepper plants compared with the control.4. The upstream and downstream segments of gene cpxRA were expanded and gainedcorresponding gene successfully. PJQ200SK::CpxRA gene knockout vector was tried toconstruct and the vector link of downstream segments had been completed; expansionconditions of Kanamycin gene was optimized.