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Staphylococcus aureus Fatty Acid Kinase FakA Modulates Pathogenesis during Skin Infection via Proteases.

ABSTRACT: Staphylococcus aureus fatty acid kinase FakA is necessary for the incorporation of exogenous fatty acids into the lipid membrane. We previously demonstrated that the inactivation of fakA leads to decreased ?-hemolysin (Hla) production but increased expression of the proteases SspAB and aureolysin in vitro, and that the ?fakA mutant causes larger lesions than the wild type (WT) during murine skin infection. As expected, necrosis is Hla dependent in the presence or absence of FakA, as both hla and hla ?fakA mutants are unable to cause necrosis of the skin. At day 4 postinfection, while the ?fakA mutant maintains larger and more necrotic abscesses, bacterial numbers are similar to those of the WT, indicating the enhanced tissue damage of mice infected with the ?fakA mutant is not due to an increase in bacterial burden. At this early stage of infection, skin infected with the ?fakA mutant has decreased levels of proinflammatory cytokines, such as interleukin-17A (IL-17A) and IL-1?, compared to those of WT-infected skin. At a later stage of infection (day 7), abscess resolution and bacterial clearance are hindered in ?fakA mutant-infected mice. The paradoxical findings of decreased Hla in vitro but increased necrosis in vivo led us to investigate the role of the proteases regulated by FakA. Utilizing ?aur and ?sspAB mutants in both the WT and fakA mutant backgrounds, we found that the absence of these proteases in a fakA mutant reduced dermonecrosis to levels similar to those of the WT strain. These studies suggest that the overproduction of proteases is one factor contributing to the enhanced pathogenesis of the ?fakA mutant during skin infection.

SUBMITTER: Ridder MJ

PROVIDER: S-EPMC7375762 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Staphylococcus aureus Fatty Acid Kinase FakA Modulates Pathogenesis during Skin Infection via Proteases.

Ridder Miranda J MJ Daly Seth M SM Triplett Kathleen D KD Seawell Nichole A NA Hall Pamela R PR Bose Jeffrey L JL

Infection and immunity 20200721 8

Staphylococcus aureus fatty acid kinase FakA is necessary for the incorporation of exogenous fatty acids into the lipid membrane. We previously demonstrated that the inactivation of fakA leads to decreased α-hemolysin (Hla) production but increased expression of the proteases SspAB and aureolysin in vitro, and that the ΔfakA mutant causes larger lesions than the wild type (WT) during murine skin infection. As expected, necrosis is Hla dependent in the presence or abse ...[more]

PMID: 32513856

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Project description:Staphylococcus aureus is capable of phosphorylating exogenous fatty acids for incorporation into the bacterium's membrane via the fatty acid kinase, FakA. Additionally, FakA plays a significant role in virulence factor regulation and skin infections. We previously showed that a fakA mutant displays altered growth kinetics in vitro, observed during the late-exponential phase of growth. Here, we demonstrate that the absence of FakA leads to key metabolic changes. First, the fakA mutant has an altered acetate metabolism, with acetate being consumed at an increased rate than in the wild-type strain. Moreover, the growth benefit was diminished with inactivation of the acetate-generating enzyme AckA. Using a mass spectrometry-based approach, we identified altered concentrations of tricarboxylic acid (TCA) cycle intermediates and both intracellular and extracellular amino acids. Together, these data demonstrate a change in carbohydrate carbon utilization and altered amino acid metabolism in the fakA mutant. Energy status analysis revealed the mutant had a similar ADP/ATP ratio to that of the wild type, but a reduced adenylate energy charge. The inactivation of fakA changed the NAD+/NADH and NADP+/NADPH ratios, indicating a more oxidized cellular environment. Evidence points to the global metabolic regulatory proteins CcpA and CodY being important contributors to the altered growth in a fakA mutant. Indeed, it was found that directing amino acids from the urea cycle into the TCA cycle via glutamate dehydrogenase was an essential component of S. aureus growth after glucose depletion. Together, these data identify a previously unidentified role of FakA in the global physiology of S. aureus, linking external fatty acid utilization and central metabolism.IMPORTANCE The fatty acid kinase, FakA, of Staphylococcus aureus plays several important roles in the cell. FakA is important for the activation of the SaeRS two-component system and secreted virulence factors like ?-hemolysin. However, the contribution of FakA to cellular metabolism has not been explored. Here, we highlight the metabolic consequence of removal of FakA from the cell. The absence of FakA leads to altered acetate metabolism and altered redox balance, as well as a change in intracellular amino acids. Additionally, the use of environmental amino acid sources is affected by FakA. Together, these results demonstrate for the first time that FakA provides a link between the pathways for exogenous fatty acid use, virulence factor regulation, and other metabolic processes.

Project description:BackgroundMethicillin-resistant Staphylococcus aureus (MRSA)-USA300 is notorious for its ability to cause community- and healthcare-acquired infections, which are even more difficult to treat when associated with a biofilm phenotype. We aimed to characterize the genetic determinants of biofilm formation in a USA300 skin abscess isolate (UAS391) that formed prolific biofilms.MethodsUSA300 S. aureus strains, TCH1516 and FPR3757, were found to be closely related based on whole genome mapping (Argus™ Optical Mapping System, Opgen Inc, Gaithersburg, USA) to UAS391 (96.3-99.1 % similarity, P=0.0151), however differed markedly in biofilm formation (P=0.0001) on a dynamic assay (BioFlux 200, Fluxion Biosciences, USA). Comparison of whole genome sequences of these strains identified differences in a total of 18 genes. Corresponding Tn (bursa aurealis-bearing) knockout mutants in these target genes were obtained from a publicly available mutant library of the same clonal lineage (USA300-JE2) and were characterized phenotypically for biofilm formation. Tn mutants showing significant differences in biofilm formation were utilized for transduction into a plasmid-cured erythromycin-sensitive derivative of UAS391 and for complementation experiments. All strains were tested on the dynamic assay, and 17h-biofilms were stained (SYTO9, Life Technologies) and fluorescence intensity quantified by microscopy (Zeiss, ImageJ). Gene expression levels in Tn and transduced mutants were studied by quantitative reverse transcriptase PCR (StepOnePlusTM, Applied Biosystems®).ResultsComparison of the sequenced genomes of TCH1516, FPR3757 and UAS391 yielded a limited number of variant genes (n=18) that were hypothesized to account for the observed difference in biofilm-forming capacity. Screening of Tn mutants disrupted in these target genes identified one mutant (NE229) bearing a transposon insertion in SAUSA300_1119 (fakA), which exhibited increased biofilm formation similar to UAS391 (P=0.9320). Transduction experiments confirmed that fakA::Tn corresponded to 1.9- to 4.6-fold increase in biofilm formation depending on the USA300 strain background (P≤0.0007), while complementation of the TCH1516 wild-type fakA allele in UAS391 resulted in a 4.3-fold reduction in biofilm formation (P<0.0001).ConclusionsThis sequential approach, consisting of strain typing, genome comparison and functional genomics, identified fakA, a recently described fatty acid kinase in S. aureus that is essential for phospholipid synthesis and also impacts the transcription of numerous virulence factors, as a negative regulator of biofilm formation in S. aureus USA300.

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Staphylococcus aureus Fatty Acid Kinase FakA Modulates Pathogenesis during Skin Infection via Proteases.

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Staphylococcus aureus Fatty Acid Kinase FakA Modulates Pathogenesis during Skin Infection via Proteases.

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