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Staphylococcus aureus Tissue Infection During Sepsis Is Supported by Differential Use of Bacterial or Host-Derived Lipoic Acid.

ABSTRACT: To thrive in diverse environments, bacteria must shift their metabolic output in response to nutrient bioavailability. In many bacterial species, such changes in metabolic flux depend upon lipoic acid, a cofactor required for the activity of enzyme complexes involved in glycolysis, the citric acid cycle, glycine catabolism, and branched chain fatty acid biosynthesis. The requirement of lipoic acid for metabolic enzyme activity necessitates that bacteria synthesize the cofactor and/or scavenge it from environmental sources. Although use of lipoic acid is a conserved phenomenon, the mechanisms behind its biosynthesis and salvage can differ considerably between bacterial species. Furthermore, low levels of circulating free lipoic acid in mammals underscore the importance of lipoic acid acquisition for pathogenic microbes during infection. In this study, we used a genetic approach to characterize the mechanisms of lipoic acid biosynthesis and salvage in the bacterial pathogen Staphylococcus aureus and evaluated the requirements for both pathways during murine sepsis. We determined that S. aureus lipoic acid biosynthesis and salvage genes exist in an arrangement that directly links redox stress response and acetate biosynthesis genes. In addition, we found that lipoic acid salvage is dictated by two ligases that facilitate growth and lipoylation in distinct environmental conditions in vitro, but that are fully compensatory for survival in vivo. Upon infection of mice, we found that de novo biosynthesis or salvage promotes S. aureus survival in a manner that depends upon the infectious site. In addition, when both lipoic acid biosynthesis and salvage are blocked S. aureus is rendered avirulent, implying an inability to induce lipoic acid-independent metabolic programs to promote survival. Together, our results define the major pathways of lipoic acid biosynthesis and salvage in S. aureus and support the notion that bacterial nutrient acquisition schemes are instrumental in dictating pathogen proclivity for an infectious niche.

SUBMITTER: Zorzoli A

PROVIDER: S-EPMC5049849 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Staphylococcus aureus Tissue Infection During Sepsis Is Supported by Differential Use of Bacterial or Host-Derived Lipoic Acid.

Zorzoli Azul A Grayczyk James P JP Alonzo Francis F

PLoS pathogens 20161004 10

To thrive in diverse environments, bacteria must shift their metabolic output in response to nutrient bioavailability. In many bacterial species, such changes in metabolic flux depend upon lipoic acid, a cofactor required for the activity of enzyme complexes involved in glycolysis, the citric acid cycle, glycine catabolism, and branched chain fatty acid biosynthesis. The requirement of lipoic acid for metabolic enzyme activity necessitates that bacteria synthesize the cofactor and/or scavenge it ...[more]

PMID: 27701474

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Project description:Staphylococcus aureus competes for myriad essential nutrients during host infection. One of these nutrients is the organosulfur compound lipoic acid, a cofactor required for the activity of several metabolic enzyme complexes. In S. aureus, these include the E2 subunits of three α-ketoacid dehydrogenases and two H proteins, GcvH of the glycine cleavage system and its paralog, GcvH-L. We previously determined that the S. aureus amidotransferase LipL is required for lipoylation of the E2 subunits of pyruvate dehydrogenase (PDH) and branched-chain 2-oxoacid dehydrogenase (BCODH) complexes. The results from this study, coupled with those from Bacillus subtilis, suggested that LipL catalyzes lipoyl transfer from H proteins to E2 subunits. However, to date, the range of LipL targets, the extent of LipL-dependent lipoic acid shuttling between lipoyl domain-containing proteins, and the importance of lipoyl relay in pathogenesis remain unknown. Here, we demonstrate that LipL uses both lipoyl-H proteins as the substrates for lipoyl transfer to all E2 subunits. Moreover, LipL facilitates lipoyl relay between E2 subunits and between H proteins, a property that potentially constitutes an adaptive response to nutrient scarcity in the host, as LipL is required for virulence during infection. Together, these observations support a role for LipL in facilitating flexible lipoyl relay between proteins and highlight the complexity of protein lipoylation in S. aureusIMPORTANCE Protein lipoylation is a posttranslational modification that is evolutionarily conserved from bacteria to humans. Lipoic acid modifications are found on five proteins in S. aureus, four of which are components of major metabolic enzymes. In some bacteria, the amidotransferase LipL is critical for the attachment of lipoic acid to these proteins, and yet it is unclear to what extent LipL facilitates the transfer of this cofactor. We find that S. aureus LipL flexibly shuttles lipoic acid among metabolic enzyme subunits, alluding to a dynamic redistribution mechanism within the bacterial cell. This discovery exemplifies a potential means by which bacteria optimize the use of scarce nutrients when resources are limited.

Project description:Methicillin-resistant Staphylococcus aureus (MRSA) is a threat to global health. Consequently, much effort has focused on the development of new antimicrobials that target novel aspects of S. aureus physiology. Fatty acids are required to maintain cell viability, and bacteria synthesize fatty acids using the type II fatty acid synthesis pathway (FASII). FASII is significantly different from human fatty acid synthesis, underscoring the therapeutic potential of inhibiting this pathway. However, many Gram-positive pathogens incorporate exogenous fatty acids, bypassing FASII inhibition and leaving the clinical potential of FASII inhibitors uncertain. Importantly, the source(s) of fatty acids available to pathogens within the host environment remains unclear. Fatty acids are transported throughout the body by lipoprotein particles in the form of triglycerides and esterified cholesterol. Thus, lipoproteins, such as low-density lipoprotein (LDL) represent a potentially rich source of exogenous fatty acids for S. aureus during infection. We sought to test the ability of LDLs to serve as a fatty acid source for S. aureus and show that cells cultured in the presence of human LDLs demonstrate increased tolerance to the FASII inhibitor, triclosan. Using mass spectrometry, we observed that host-derived fatty acids present in the LDLs are incorporated into the staphylococcal membrane and that tolerance to triclosan is facilitated by the fatty acid kinase A, FakA, and Geh, a triacylglycerol lipase. Finally, we demonstrate that human LDLs support the growth of S. aureus fatty acid auxotrophs. Together, these results suggest that human lipoprotein particles are a viable source of exogenous fatty acids for S. aureus during infection.IMPORTANCE Inhibition of bacterial fatty acid synthesis is a promising approach to combating infections caused by S. aureus and other human pathogens. However, S. aureus incorporates exogenous fatty acids into its phospholipid bilayer. Therefore, the clinical utility of targeting bacterial fatty acid synthesis is debated. Moreover, the fatty acid reservoir(s) exploited by S. aureus are not well understood. Human low-density lipoprotein particles represent a particularly abundant in vivo source of fatty acids and are present in tissues S. aureus colonizes. Herein, we establish that S. aureus is capable of utilizing the fatty acids present in low-density lipoproteins to bypass both chemical and genetic inhibition of fatty acid synthesis. These findings imply that S. aureus targets LDLs as a source of fatty acids during pathogenesis.

Dataset Information

Staphylococcus aureus Tissue Infection During Sepsis Is Supported by Differential Use of Bacterial or Host-Derived Lipoic Acid.

Publications

Staphylococcus aureus Tissue Infection During Sepsis Is Supported by Differential Use of Bacterial or Host-Derived Lipoic Acid.

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