Molecular characterization of the arginine deiminase pathway, a critical player for insisting acidic condition and intracellular survival in laribacter Hongkongensis

Abstract

The beta-proteobacterium Laribacter hongkongensis is a novel discovered bacterium associated with invasive bacteremic infections and gastroenteritis. Its mechanisms of adaptation to various environmental niches and host defense evasion are largely unknown. The first challenge that gastrointestinal bacterium has to face is the hostile acidic environment of the stomach after passaging oral route. In previous study, we found that two adjacent arc operons are under independent-transcriptional control and essential for acid resistance in vitro and mice model and intracellular survival in macrophages. Furthermore, L. hongkongensis also encodes duplicate copies of argA and argB genes from the arginine biosynthesis pathway, which is a rarely encountered situation in bacteria. We dissected the respective transcriptional responses of the two arc operons and the two copies of argA and argB genes in L. hongkongensis that were exposed to different environmental stresses and in macrophages, which were regulated by a transcriptional regulator named ArgR. In this study, we further demonstrate another regulator named FNR by RNA-sequencing, which could specifically regulate the expression of arginine metabolism genes under anaerobicity. FNR activates the ADI pathway by binding to the FNR boxes in the promoter regions of arc operons. FNR and ArgR affect the expression of each other. Bacterial survival of fnr mutant in macrophages is significantly decreased when compared to that of the wild-type; whilst expression of fnr gene increases 8 h post-infection. Our results show that FNR and ArgR cooperate to control the biological fitness of L. hongkongensis under anaerobicity by finely regulating the arginine metabolism pathways.