The bacillithiol pathway is required for biofilm formation in Staphylococcus aureus

Abstract

Staphylococcus aureus is a major human pathogen that can cause infections that range from superficial skin and mucosal infections to life threatening disseminated infections. S. aureus can attach to medical devices and host tissues and form biofilms that allow the bacteria to evade the host immune system and provide protection from antimicrobial agents. To counter host-generated oxidative and nitrosative stress mechanisms that are part of the normal host responses to invading pathogens, S. aureus utilizes low molecular weight (LMW) thiols, such as bacillithiol (BSH). Additionally, S. aureus synthesizes its own nitric oxide (NO), which combined with its downstream metabolites may also protect the bacteria against specific host responses. We have previously shown that LMW thiols are required for biofilm formation in Mycobacterium smegmatis and Pseudomonas aeruginosa. Our data show that the bshC mutant, which is defective in the last step of the bacillithiol pathway and lacks BSH, is impaired in biofilm formation. We also identify a putative S-nitrosobacillithiol reductase (BSNOR), similar to a S-nitrosomycothiol reductase found in M. smegmatis, and show that the BSNOR mutant has reduced levels of BSH and decreased biofilm formation. Our studies also show that NO plays an important role in biofilm formation and that acidified sodium nitrite severely reduces biofilm thickness. These studies provide insight into the roles of oxidative and nitrosative stress mechanisms on biofilm formation and indicate that bacillithiol and nitric oxide are key players in normal biofilm formation in S. aureus.\n\nImportanceStaphylococcus aureus is the most frequent cause of biofilm-associated infections in hospital settings. The biofilm mode of growth allows the pathogen to escape the host immune response and is extremely difficult to combat, as biofilms are highly resistant to physical and chemical stressors. As outbreaks of antibiotic-resistant bacterial strains become more commonplace, it is essential to understand the pathways involved in biofilm formation in order to target this important virulence factor. Low molecular weight thiols enable S. aureus to combat oxidative and nitrosative stress mechanisms that are used by host cells to defend against infection. Our findings indicate that bacillithiol and nitric oxide, which are produced by S. aureus to combat these host generated stressors, are important for biofilm development, and that disruption of these pathways results in biofilm defects. In the long term, this work may lead to new solutions to eradicate S. aureus biofilms in the clinic.