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Characterizing the Staphylococcus aureus fatty acid degradation operon

ABSTRACT: Staphylococcus aureus can supplement its endogenous fatty acid synthesis pathway (FASII) with exogenous fatty acids it acquires from the environment through the fatty acid kinase (Fak) complex. While S. aureus has been thought to not degrade fatty acids, it does possess a potential fadXDEBA locus that contains all the genes necessary for -oxidation. Using mRNA analysis, we determined that the fadXDEBA operon can be found on one polycistronic mRNA. Moreover, we identified the fadX promoter and a putative binding site within this region that is consistent with negative regulation by the metabolism-responsive regulator, Carbon Catabolite Protein A (CcpA). Indeed, in the absence of glucose or CcpA, we saw the fadXDEBA operon was derepressed. S. aureus is annotated to lack the crotonase domain of FadB; however, new analysis indicates it is present. To test the functionality of the S. aureus FadB, we performed complementation assays with E. coli fad mutants using minimal media supplemented with single fatty acids. We were able to restore growth of E. coli fad mutants when providing safadBA genes on a plasmid and demonstrate that the SaFadB crotonase domain is required for complementation. Together, these data demonstrate the SaFadBA proteins are functional within a well characterized fatty acid degradation system and the fadXDEBA operon is under strong catabolite repression.

ORGANISM(S): Staphylococcus aureus

PROVIDER: GSE299037 | GEO | 2025/06/05

REPOSITORIES: GEO

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Project description:Background The catabolite control protein A (CcpA) is a member of the LacI/GalR family of transcriptional regulators controlling carbon-metabolism pathways in low-GC Gram positive bacteria. It functions as a catabolite repressor or activator, allowing the bacteria to utilize the preferred carbon source over secondary carbon sources. This study is the first CcpA-dependent transcriptome and proteome analysis in S. aureus wild type and ccpA-deleted mutant, focussing on short-time effects of glucose under stable pH conditions. Results The addition of glucose to exponentially growing S. aureus increased enzymes of glycolytic pathway, indicating a higher glycolytic activity, while proteins required for the complete oxidation in the TCA cycle were repressed via CcpA. Phosphotransacetylase and acetate kinase, converting acetylCoA to acetate with a concomitant substrate-level phosphorylation were neither regulated by glucose nor by CcpA. Most CcpA directly repressed genes were involved in utilization of amino acids as secondary carbon sources. More genes were found to be differentially expressed by CcpA in a glucose-independent manner than in the classical, glucose dependent way, suggesting that glucose-independent regulation by CcpA may be of particular importance in S. aureus. In the presence of glucose, CcpA was found to regulate expression of genes involved in metabolism, but that of genes coding for virulence determinants. Conclusions This study identified the CcpA regulon of exponentially growing S. aureus, for the first time. As in other bacteria, the CcpA-regulon of S. aureus comprised a large amount of metabolic genes but also some 50 genes associated with virulence. CcpA seemed to work in a glucose- as well as glucose-independent way. The transcriptomes of strain Newman and its isogenic ccpA-deleted mutant were determined in early exponential growth and 30 min after the addition of 10 mM glucose, under controlled pH conditions. In the absence of glucose, the wild type grew slightly faster than the mutant, reaching an OD600 of 1 approximately 20 min earlier than the mutant. Adding 10 mM glucose at OD600 1 increased the growth rate of the wild type but had only a minor effect on that of the mutant. 60 min after glucose addition, glucose was depleted down to 0.3 mM by the wild type, while still 3 mM glucose was left in the culture of the mutant. Despite increased glucose consumption rates in the wild type, acetate production was only slightly enhanced compared to the mutant. No lactate was excreted at any time point sampled. Acidification of the medium upon glucose metabolism was prevented by buffering, maintaining a pH of 7.5 for both strains and under both growth conditions for at least 2 h after glucose addition, allowing to rule out any pH effects.

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Characterizing the Staphylococcus aureus fatty acid degradation operon

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