The Brucella spp encounter stressful environment inside their host cells.The Lon protein is an important protease related to cellular protein degradation and resistance to stress responses in Brucella.However,the molecular mechanism between Lon protein and stress response was still unknown.In this study,it was found that the lon mutant exhibited obvious growth defect in TSB medium,compared with its parent strain.In addition,our results indicated that Lon protein was involved in resistance to various stress conditions and all the β-lactam antibiotics tested.Although deletion of this protease did not affect Brucella virulence in macrophage,the mutant strain was significant attenuation in mice infection model at 1 week post infection,and the expression level of several cytokine genes was significantly changed in vivo.To gain insight into the genetic basis for the distinctive phenotypic properties exhibited by the lon mutant strain,RNA-seq was performed,and the result showed that various genes involved in stress response,quorum sensing and transcriptional regulation were significantly different expressed in Δlon strain.Overall,these studies have preliminary uncovered the molecular mechanism between Lon protease,stress response and bacterial virulence.