Gene bb0318 Is Critical for the Oxidative Stress Response and Infectivity of Borrelia burgdorferi.

A greater understanding of the molecular mechanisms that Borrelia burgdorferi uses to survive during mammalian infection is critical for the development of novel diagnostic and therapeutic tools to improve the clinical management of Lyme disease. By use of an in vivo expression technology (IVET)-based approach to identify B. burgdorferi genes expressed in vivo, we discovered the bb0318 gene, which is thought to encode the ATPase component of a putative riboflavin ABC transport system. Riboflavin is a critical metabolite enabling all organisms to maintain redox homeostasis. B. burgdorferi appears to lack the metabolic capacity for de novo synthesis of riboflavin and so likely relies on scavenging riboflavin from the host environment. In this study, we sought to investigate the role of bb0318 in B. burgdorferi pathogenesis. No in vitro growth defect was observed for the Δbb0318 clone. However, the mutant spirochetes displayed reduced levels of survival when exposed to exogenous hydrogen peroxide or murine macrophages. Spirochetes lacking bb0318 were found to have a 100-fold-higher 50% infectious dose than spirochetes containing bb0318 In addition, at a high inoculum dose, bb0318 was found to be important for effective spirochete dissemination to deep tissues for as long as 3 weeks postinoculation and to be critical for B. burgdorferi infection of mouse hearts. Together, these data implicate bb0318 in the oxidative stress response of B. burgdorferi and indicate the contribution of bb0318 to B. burgdorferi mammalian infectivity.