PROJECT SUMMARY
Staphylococcus aureus asymptomatically colonizes 30% of the human population. However, the bacterium can
breach innate host defenses to gain access to deeper tissues and vasculature allowing it to infect diverse tissue
sites such as the heart, lungs, blood, bones, and skin. Despite distinct nutritional limitations at these sites, we
know comparatively little about how S. aureus adapts its metabolism to survive and cause infection. To better
combat infections caused by S. aureus, it is imperative to understand how the bacterium changes metabolic flux
to adapt to nutritional restrictions imposed by host tissues. Several metabolic enzyme complexes involved in S.
aureus central metabolism are activated via the covalent linkage of the cofactor lipoic acid to E2 subunits. The
transfer of lipoic acid to E2 subunits is mediated by the amidotransferase, LipL. Notably, LipL transfers lipoic
acid to a critical enzyme used in glycolysis, pyruvate dehydrogenase. Pyruvate dehydrogenase use pyruvate to
generate acetyl-CoA, a molecule that is crucial for several downstream metabolic pathways. Our prior studies
and preliminary data established that LipL is genetically and functionally coupled to the phosphotransacetylase,
Pta. Pta catalyzes the generation of acetyl-phosphate from pyruvate dehydrogenase-derived acetyl-CoA. Acetyl-
phosphate is subsequently delivered to acetate kinase, AckA, to generate ATP during overflow metabolism. We
recently demonstrated a potential interaction between Pta and LipL and found that a ¿lipL mutant produces
negligible acetate in culture. Furthermore, the loss of either the pta or lipL gene results in significant attenuation
in the host. Thus, we hypothesize that a functional link is established between Pta and LipL that enhances
glycolytic flux by coupling pyruvate dehydrogenase activity (lipoylation) to acetogenesis (Pta-AckA) to promote
energy balance and survival during infection (Aim 1). Additionally, we found that acetate production still occurs
in a ¿pta mutant, suggesting compensatory enzymes - such as the pyruvate oxidase CidC - could be promoting
acetogenesis and might affect virulence. Furthermore, we found that expression of lipL under the control of high
and low expressing promoters regulated the transition from acetogenesis to TCA cycle activity. These results
led us to hypothesize that LipL levels/activity establish a metabolite signature that controls (i) acetogenesis via
CidC and (ii) TCA cycle activity to promote energy balance and S. aureus survival during infection (Aim 2). In
Aim 1, we will determine how LipL interfaces with Pta to control energy balance during overflow metabolism. In
Aim 2, we will investigate how LipL governs metabolic flux through CidC and the TCA cycle. Together, these
Aims will lead to a better understanding of how LipL promotes metabolism, energy balance, and virulence in Sa.