Research Of The Growth Promotion Mechanism Of Two Endophytic Bacteria On Potato

Potato is an important food crop in China.The use of endophytic bacteria with growth promoting and biocontrol effects in potato production can not only reduce the occurrence of diseases,but also promote growth and increase production.Our laboratory screened two endophytic bacteria(Q2H1 and Q2H2)from potato roots in the early stage,which have a promoting effect on the growth of Chinese cabbage.This study focuses on these two endophytic bacteria and analyzes their growth promoting effects on potato plants.1.The results of growth-promoting characteristics test showed that Q2H1 had the ability of nitrogen fixation,dissolved organic phosphorus,siderophore production,IAA production and ammonia production.Q2H2 has the ability of nitrogen fixation,dissolved organic phosphate,antagonism,siderophore production,IAA production and ammonia production.Abiotic(p H,temperature,salt)stress test showed that the p H tolerance range of Q2H1 was 5-9,the suitable growth temperature was 20-30°C,and the suitable salt concentration was 1%-3%.The p H tolerance range of Q2H2 was 5-9,the suitable growth temperature was 15-30°C,and the suitable salt concentration was 1-5%.2.The plate antagonism test showed that Q2H2 had inhibitory effect on a variety of pathogenic fungi,and Q2H1 had no antagonistic activity.Hydrolytic enzyme test showed that Q2H1 had the ability to produce protease,and Q2H2 had the ability to produce protease,cellulase and β-1,3-glucanase.The inhibitory effects of Q2H2 non-volatile and volatile substances on pathogenic fungi indicated that strain Q2H2 could produce nonvolatile and volatile substances that inhibited the growth of various pathogenic fungi.3.The pot experiment showed that the fresh weight and root weight of potato plants inoculated with Q2H1 increased by 14.5%(6.83 g)and 67.57%(1.5 g)compared with the control.The root weight of potato plants inoculated with Q2H2 increased by 44.4%(2.26 g)compared with the control,and the difference was significant.The pot biological control experiment showed that the control effect of potato inoculated with Q2H2 on Fusarium wilt reached 49.29%,which was slightly better than that of chemical control(39.14%).4.The possible growth promoting and antagonistic mechanisms of the two endophytic bacteria were revealed by bacterial genome sequencing.The results showed that Q2H1 was Peribacillus sp.,and Q2H2 was Bacillus sp..The whole genome sequencing results showed that the Q2H1 genome contained a chromosome with a size of about 5.65 MB and three plasmids.ANI and comparative genomic analysis showed that Q2H1 was identified as Peribacillus frigoritolerans.The genes related to nitrogen fixation were divided into three groups: nitrogen fixation(nif U,suf U,sal A and nif S),nitrogen metabolism(nir A,nrt B and nas A)and glutamate synthesis(gln A,glt B,glt B,glt D and gud B).Five phosphate solubilizing genes,pho U,pst B,pst A1,pst C and pst S,were annotated to dissolve phosphate.We also found a siderophore gene cluster on Q2H1 chromosome,including seven genes(rbs R,rhbf,rhb E,rhb D,rhb C,rhb A,ddc and an unknown gene).In addition,IAA related gene trp ABCDEFGDPS and secondary metabolite gene cluster were also annotated.The genome of Q2H2 contains only one chromosome of about 3.96 MB.ANI and comparative genomic analysis showed that Q2H2 was identified as Bacillus halotolerans.The genes related to growth promotion and antagonism in its genome were analyzed.Nitrogen fixation related genes nif S and nif U are important components of nitrogenase.Two ammonia production pathways were found to be regulated by gud B,roc G,nas D and nas E genes.A group of phosphate transporters encoded by pst B,pst A,pst C and pst S were annotated,which may be related to phosphate solubilization.Genes fhu C,fhu G,fhu B and fhu D were annotated as encoding iron complex transporters,which may be related to siderophores.The trp ABFCDE gene encodes related enzymes in the IAA synthesis pathway.Genes encoding endoglucanase and α-amylase,cellulase activity related genes gmu D and gan B,chitinase activity related genes sle L and ydh D were annotated.Biofilm synthesis genes tas A,bsl A and bsl B,volatile compounds 2,3-butanediol(als D,ilv ABCDEHKY),methyl mercaptan(met H),isoprene(isp E)may be involved in the biocontrol mechanism of strain Q2H2.