GSE99563
The Staphylococcus aureus a-Acetolactate Synthase ALS Confers Resistance to Nitrosative Stress
Staphylococcus aureus is a worldwide pathogen that colonizes the human nasal cavity and is a major cause of respiratory and cutaneous infections. In the nasal cavity, S. aureus thrives with high concentrations of nitric oxide (NO) produced by the innate immune effectors and has available for growth slow metabolizing free hexoses, such as galactose. Here, we have used deep sequencing transcriptomic analysis (RNA-Seq) and 1H-NMR to uncover how S. aureus grown on galactose, a major carbon source present in the nasopharynx, survives the deleterious action of nitric oxide. We observed that, like on glucose, S. aureus withstands high concentrations of NO when using galactose. However, most likely this is achieved through a distinct metabolism that relies on the increased production of amino acids, such as glutamate, threonine and branched-chain amino acids. Moreover, we found that under these conditions the a-acetolactate synthase (ALS) enzyme, which converts pyruvate into a-acetolactate, plays a role in the resistance of S. aureus to NO. However, the role of ALS is not restricted to galactose but also extends to cells growing on glucose. The results suggest that ALS prevents intracellular acidification, promoting the production of branched-chain amino acids and activation of the TCA cycle. We show that ALS contributes to the successful infection of murine macrophages. Furthermore, ALS is also shown to contribute to the resistance of S. aureus to beta-lactam antibiotics such as methicillin and oxacillin. Overall design: mRNA profiles of S. aureus galactose-grown cells unexposed and exposed for 3h with NO were generated by deep sequencing, in duplicate, using an Ion Proton™ Sequencer.