The Extract Of Bacillus Sp.BR3 Inhibit Function Of The GacS/GacA Two Component System In Pseudomonas Syringae Pv.tomato DC3000

The GacS/GacA two-component system is important for virulence in many plant pathogenic bacteria.Therefore,disruption the GacS/GacA two-component system is a promising strategy for prevention and control of the GacS/GacA system-mediated bacterial infections.In the present study,we used a gradient dilution method to isolation rhizobacteria,culture and screen the secondary metabolism that interfering the expression of gacS gene of strain Pseudomonas syringae pv.tomato DC3000(p970Gm-gacSp).One candidate inhibitor bacterium,BR3 was identified as a Bacillus strain based on 16 S rDNA gene sequence analysis.Our data showed that the expression of gacS gene of strain DC3000 was significantly repressed by the extract of strain BR3.Our data further indicated that besides the gacS gene,the GacA-dependent small non-coding RNA genes rsm Y and rsm Z were repressed at the transcriptional level when strain DC3000 was treated with the extract from strain BR3.Importantly,bacterial motility,the production of type three secretion system effector Avr Pto,and the plant hypersensitive response(HR)triggered by DC3000 was also influenced by the extract from strain BR3.Moreover,the extract of strain BR3 also affect the production of 2,4-diacetylphloroglucinol(2,4-DAPG)in Pseudomonas fluorescens 2P24,which positively regulated by the GacS/GacA system.Greenhouse experiments showed that the BR3 extract significantly inhibited the pathogenicity of strain DC3000 on Arabidopsis leaves and the virulence of Pectobacterium carotovorum subsp.carotovorum Z3-3 on Chinese cabbage.In addition,five compounds from the BR3 extract were isolated using column chromatography,and the structures of these compounds were determined by NMR(nuclear magnetic resonance)spectroscopy,which are 2-phenylacetamide,L-phenyllactic acid,11-methyl-11-hydroxyldodecanoic acid amide,cyclo-(Leu-Leu),and cyclo-(L-Val-L-Pro).In summary,the extract of Bacillus BR3 can inhibit the function of the GacS/GacA two-component system,which not only provides a novel method to explore the upstream environmental factors of this system,but also is a sensible strategy to control bacterial infection.