Characterizing the Staphylococcus aureus fatty acid degradation operon

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Staphylococcus aureus utilizes fatty acid synthesis (FASII) and can import exogenous fatty acids via the fatty acid kinase (Fak) complex.
• The bacterium was previously believed to lack a functional fatty acid degradation (Fad) pathway, with studies suggesting the absence of a crucial crotonase domain in its FadB protein.
• Limited prior research and potential misannotations contributed to the assumption that Staphylococcus aureus could not degrade fatty acids.

Purpose of the Study:

• To investigate the presence and functionality of a fatty acid degradation (Fad) pathway in Staphylococcus aureus.
• To identify the regulatory mechanisms governing the expression of the putative Fad pathway genes.
• To challenge the long-held belief that Staphylococcus aureus lacks the capacity for fatty acid degradation.

Main Methods:

• mRNA analysis was employed to confirm the existence of the fadXDEBA operon as a single polycistronic mRNA.
• Promoter identification and analysis revealed a putative binding site for the Carbon Catabolite Protein A (CcpA) regulator.
• Complementation assays in E. coli fad mutants using Staphylococcus aureus fadBA genes were performed to assess protein functionality.

Main Results:

• The fadXDEBA operon was confirmed to be transcribed as a single mRNA unit.
• Expression of the fadXDEBA operon was found to be under strong catabolite repression, particularly in the presence of glucose, and derepressed in the absence of glucose or CcpA.
• Complementation assays demonstrated that Staphylococcus aureus FadB possesses a functional crotonase domain, essential for restoring growth of E. coli fad mutants.

Conclusions:

• Staphylococcus aureus possesses a functional fatty acid degradation (Fad) pathway, contrary to previous assumptions.
• The fadXDEBA operon is subject to significant catabolite repression by CcpA, explaining its previously undetected activity.
• These findings necessitate a revised understanding of fatty acid metabolism in Staphylococcus aureus, integrating both synthesis and degradation pathways.