Exogenous fatty acid utilization by Staphylococcus aureus

PROJECT SUMMARY Fatty acids are an indispensable part of life since they are an essential component of membranes. In addition, they can serve a variety of other purposes, from an energy source to part of signaling molecules. Most bacteria can generate their own fatty acids through a biosynthesis pathway. However, bacteria can also scavenge fatty acids from the environment, including other bacteria and plant or mammal sources. This includes both free fatty acids and as components of larger molecules. These external fatty acids can be used by bacteria to supplement the fatty acid biosynthetic pathway or as an energy source. In Gram-positive bacteria, external fatty acids can be incorporated directly to lipids through the FakAB system that was first discovered in Staphylococcus aureus. In the case of pathogens like S. aureus, fatty acids are abundant in the host. However, the mechanism by which the FakAB system functions is unclear due to limited biochemical and structural data. This will be the focus of Aim 2. Many bacteria can also degrade external fatty acids using a fatty acid degradation pathway. However, S. aureus has been thought to lack this pathway. Yet, a recent report and the preliminary data of this application suggests otherwise. This system is the focus of Aim 1. In addition to these two pathways that would utilize fatty acids, S. aureus transcriptionally responds to fatty acids. In the case of host fatty acids, this occurs at concentrations that do not impact cellular growth and respiration, even though changes in these cellular processes have long been proposed to be the reason why. Aim3 will build upon these studies to determine how fatty acids impact S. aureus gene expression. Specifically, Aim 1 uses newly constructed mutants combined with mass spectrometry to understand regulation of the S. aureus fatty acid degradation pathway while also demonstrating its metabolic potential. Aim 2 uses cell-based assays along with structural and biochemical assays, combined with key amino acid substitutions, to interrogate the FakAB complex. Aim 3 builds upon prior research showing that S. aureus responds transcriptionally to fatty acids. It utilizes RNAseq to dissect transcriptional responses to fatty acids as a signal versus when their perturb metabolic function. It also uses protein topology studies to determine the mechanism by which this occurs.