Preliminary Study On The Mode Of Action Of Antibiotic Shenqinmycin To Xanthomonas Oryzae Pv. Oryzae

Shenqinmycin is a novel antibiotic with the effective component phenazine-1-carboxylic acid originated from microorganisms. It is extracted from an effective biocontrol strain M18 that was isolated from sweet melon rhizosphere in Shanghai suburb in 1996 by Pro.Xu of Shanghai Jiaotong University. It can effectively inhibit the growth of a series of crop pathogenic bacteria, has many characteristics, such as safe, efficient, environmentally friendly, and is a new type of green pesticides microbial sources. The toxicity of shenqinmycin against Xanthomonas.oryzae pv.Oryzae was studied by Zhen Wenjun. The results showed that shenqinmycin strongly inhibited the growth of Xoo with the EC50 value of 0.110μg/ml and minimum inhibitory concentration was less than 12.5 ug/ml. When Shenqinmycin is 200 ug.a.i./ml, the control effect up to 79.81%.The protective effect is good, however, treatment effect is not ideal and showing its potential applications against Xoo.Mechanism of shenqinmycin has not been reported in the literature, at least to the best of our knowledge, but its analogs 1-hydroxyphenazine is known.1-hydroxyphenazine during pathogenesis and competition are attributed primarily to their ability to generate reactive oxygen species (ROS) in other organisms and tissues.This is due to the ability of phenazines to accept or donate electrons because of their aromatic structure. Whether they accept or donate electronsis dependent on their redox potential relative to that of other electron transfer compounds in the cell. From the view point of biology and biochemistry, Doctor Xu Shu speculated shenqinmycin may inhibit the expression of a subunit gene of NADH dehydrogenase complex I, which causes the inhibition of bacterial growing. In order to further define the mechanism of shenqinmycin on Xoo, physiological and biochemical metabolism and gene knockout are adopted in thisresearch and results are obtained as listed below:Biolog Microbial identification found that there are differences between the wild strains ZJ173 and shenqinmycin treatment, there are some differences in the regularity. Citric Acid, a-Ketoglutaric acid, L(-)-Malicacid are different largly, affect the synthesis of ATP and NADH. Pyruvate dehydrogenase E1 activity test result in vitro and crude enzyme solution shows shenqinmycin has significant effect on the activity. Ability to generate reactive oxygen test shows that different concentration of shenqinmycin possesses significantly. Besides, with the increase of concentration, the amount of reactive oxygen is increased. While with the change of time, the rate of reactive oxygen generation have begun to slow down. This proved shenqinmycin may more intense in the early stage. Above all, we speculated shenqinmycin have a certain impact on the energy metabolism of Xoo.we adopted a novel target inserted mutagenesis in Xoo through single exchange by a vector pK18mobGII and knock-out mutagenesis for single and multiple genes in through two homologous crossover events mediated by a suicide vector pKMSl containing a sacB gene. Successfully obtain six knock-out muants(ANuoD, ANuoE, ANuoF, ANuoI, AN uoN,△ndhF). The EC50 values to shenqinmycin, generation of reactive oxygen, anti-oxidative ability of six knock-out muants were increased compared with ZJ173. However, the mutation of these six genes didn’t affect the growth rate of xoo and the EPS production. Yet the pathogenicity of rice wasn’t affect. This demonstrate genes (nuoD,nuoE, nuoF,nuoI,nuoN and ndhF) are related to action target of shenqinmycin to Xoo.Above all, on the one hand we spectulated shenqinmycin may affect the transcript, translation, peptide extension or peptide folding, which may cause composition or conformation changes of complex I, on the other hand we estimated shenqinmycin may accept or donate electronsis dependent on their redox potential relative to that of other electrontransfer compounds in the strain, block he electron transport in ETC and causes the proton gradient between two sides of cytomembrane that interference ATP synthesis by lacking of protonmotive force and accumulation excess reactive oxygen which finally causes death of mycelium.