The Study Of Quorum-sensing System In Bradyrhizobium Japonicum USDA110 Responding To Environme Ntal Stress

Bradyrhizobium japonicum USDA110 is a genus of Gram-negative soil bacteria,which can enter host legumes and fix the atmospheric nitrogen.Both the plants and bacteria benefit from the mutualistic interaction: the plant obtains the nitrogen,which it needs to synthesize the proteins,while the bacteria gain the carbon from the plant and secure environment to live within the plant.The plant-rhizobium interaction plays a decisive role in the biological nitrogen fixation cycle,food safety and ecological protection.However,the low survival capacity of Bradyrhizobium in extreme environmental stress,such as desiccation,has become the limiting factor for improving the efficiency of this symbiotic process.As described in many other bacteria,the quorum-sensing(QS)system governs the organism survival under environmental stress.Here our study accessed the bacterial capacity survival ability controlled QS system in Bradyrhizobium japonicum USDA110 under desiccation stress condition.The QS-deficient strains with bjaI gene or bjaR gene deletion were subjected cell survival test and the bacterial viability was determined post desiccation stress treatment oh,18 h,48h,72 h.The bacterial colonies counting result showed that QS-deficient strain had no obvious preference in the cell viability co mparing to the WT strain,suggesting the QS have a silent respond to the desiccation stress.To further survey the molecular mechanism responsible for the inactive QS,the transcriptome analysis was perform and confirmed that QS-deficient strain have similar gene expression patterns with WT strain.To query the role of QS in Bradyrhizobium japonicum USDA110 controlling the biophysical process,the bacterial biofilm formation,growth rate,mobility and nodulation were testin both WT and QS-deficient strains.The results indicated that QS-deficient strain have advantage only in grow the rate,but not in the biofilm formation,motility and plant nodulation aspects,of which the molecular mechanism still need to be elucidated in future.Further,the genes induced by desiccation stress were screen and identified in the genomic level through transcriptome sequencing.Gene enrichment analysis,such as GO and K EGG pathway enrichment,showed that those desiccation-induced genes involved in many biological processes,which were interpret and showed by the gene-gene interaction network.Meanwhile,mutations arose in the genomic DNA,including single nucleotide polymorphism(SNP),insertion(IN)and deletion(DEL)and RN A new transcripts(mRN As and small RNAs),were also identified,providing abundant targets for the future anti-desiccation research.Our study here reported the exceptional silent responding of QS system in desiccation stressed Bradyrhizobium japonicum USDA110,establishing a framework for further understanding of not only the QS regulation molecular mechanism but also the QS biological functions under stress environments.The transcriptome data mining here also can serve as a powerful resource for future anti-desiccation and plant-Bradyrhizobium interaction study.