Aug 2026· Journal of Bacteriology· 0 citations· 100 references
Medicine
TL;DR
A model in which the MbcS-dependent pathway enables S. aureus to scavenge BCFA precursors under nutrient-limited conditions, providing a competitive advantage in polymicrobial environments is supported.
Abstract
ABSTRACT Staphylococcus aureus is one of the most frequently co-isolated pathogens in polymicrobial infections, where interspecies interactions contribute to enhanced virulence, persistence, and antimicrobial tolerance. Nutrient availability plays a central role in these interactions as microorganisms compete for resources to sustain essential cellular processes. For instance, branched-chain amino acids (BCAAs) are critical for protein synthesis, and valine synthesis pathway precursors are essential for energy production. In S. aureus, BCAAs are also the precursors for branched-chain fatty acids (BCFAs), the dominant fatty acids in the S. aureus membrane. We previously identified a second pathway that uses branched-chain carboxylic acids (BCCAs) and the high-affinity acyl-CoA synthetase MbcS to catalyze the formation of primers for BCFA synthesis. However, the physiological role of this pathway and the conditions triggering its activation remain unclear. Here, we show that mbcS is restricted to S. aureus and closely related human-associated staphylococci. Phylogenetic analyses suggest that MbcS arose from a refunctionalization event and represents a non-orthologous replacement for the phosphotransbutyrylase (Ptb) and butyrate kinase (Buk) enzymes. Consistent with this model, Ptb and Buk from Staphylococcus pseudintermedius catalyze the formation of branched-chain acyl-CoAs from BCCAs, but only at high substrate concentrations. We further show that mbcS expression is upregulated in a CodY-deficient strain, implicating this pathway in BCAA-limited conditions. In support, we show that MbcS is required for optimal fitness during intra-species competition. Together, our findings support a model in which the MbcS-dependent pathway enables S. aureus to scavenge BCFA precursors under nutrient-limited conditions, providing a competitive advantage in polymicrobial environments. IMPORTANCE Staphylococcus aureus is a major contributor to polymicrobial infections, where competition for nutrients can influence bacterial physiology and survival. A deeper understanding of how S. aureus adapts to nutrient limitation is therefore essential to explain its success as a human pathogen. In S. aureus, the acyl-CoA synthetase MbcS supports branched-chain fatty acid (BCFA) synthesis from branched-chain amino acid (BCAA)-derived carboxylic acids and aldehydes, which are released into the environment as by-products of bacterial metabolism. Herein, we provide evidence that S. aureus acquired the acyl-CoA synthetase MbcS as an adaptive trait. This metabolic innovation allows this bacterium to maintain membrane homeostasis under nutrient limitation and compete against neighboring bacteria. Our findings highlight an adaptive strategy that may contribute to the persistence of S. aureus in polymicrobial infections. Staphylococcus aureus is a major contributor to polymicrobial infections, where competition for nutrients can influence bacterial physiology and survival. A deeper understanding of how S. aureus adapts to nutrient limitation is therefore essential to explain its success as a human pathogen. In S. aureus, the acyl-CoA synthetase MbcS supports branched-chain fatty acid (BCFA) synthesis from branched-chain amino acid (BCAA)-derived carboxylic acids and aldehydes, which are released into the environment as by-products of bacterial metabolism. Herein, we provide evidence that S. aureus acquired the acyl-CoA synthetase MbcS as an adaptive trait. This metabolic innovation allows this bacterium to maintain membrane homeostasis under nutrient limitation and compete against neighboring bacteria. Our findings highlight an adaptive strategy that may contribute to the persistence of S. aureus in polymicrobial infections.
ABSTRACT The genus Streptococcus contains some of the most important commensals and pathogens of the human microbiome. To obtain the fatty acids required for cell membranes, Streptococcus either produce fatty acids de novo through the fatty acid biosynthesis (fab) pathway or uptake host fatty acids through the fatty acid kinase (fak) pathway. Although both the fab and fak pathways represent potential therapeutic targets to prevent or treat infection, progress is limited because of an incomplete understanding of taxon-to-taxon variability in streptococcal lipid metabolism. Here, we examined the role of de novo monounsaturated fatty acid (MUFA) synthesis in physiology and virulence-associated traits in Streptococcus mutans, Streptococcus pyogenes, and Streptococcus pneumoniae, three major pathogens that cause disease at distinct body sites. In all three species, deletion of fabM abolished MUFA production and caused severe growth defects, decreased stress tolerance, increased antibiotic susceptibility, and defects in cell viability, morphology, and division. In S. mutans, loss of fabM also markedly reduced competence signaling and production of the mutacin IV bacteriocin. Deletion of fabM increased susceptibility to killing by human neutrophils in S. mutans and S. pneumoniae, but not S. pyogenes. Together, these findings illustrate that MUFA synthesis is broadly important for streptococcal physiology and cell membrane homeostasis, while its contribution to pathogenesis is strongly species- and context-dependent, providing leads to guide the development of novel therapeutic and/or preventative strategies. IMPORTANCE Streptococcus spp. exert profound effects on human health, with several species causing significant morbidity and mortality. Although streptococcal fatty acid biosynthesis and utilization are attractive metabolic targets for development of therapeutics, this opportunity is vexed by an incomplete understanding of taxon-to-taxon variability in lipid metabolism. In this study, the role of de novo monounsaturated fatty acid (MUFA) synthesis in physiology and virulence-associated traits was examined in Streptococcus mutans, Streptococcus pyogenes, and Streptococcus pneumoniae, three major pathogens that cause disease at distinct body sites. MUFA synthesis was important for stress and antibiotic tolerance across all three species, while its impact on virulence was species- and context-dependent. Overall, these discoveries provide leads to guide the development of novel therapeutic and/or preventative strategies. Streptococcus spp. exert profound effects on human health, with several species causing significant morbidity and mortality. Although streptococcal fatty acid biosynthesis and utilization are attractive metabolic targets for development of therapeutics, this opportunity is vexed by an incomplete understanding of taxon-to-taxon variability in lipid metabolism. In this study, the role of de novo monounsaturated fatty acid (MUFA) synthesis in physiology and virulence-associated traits was examined in Streptococcus mutans, Streptococcus pyogenes, and Streptococcus pneumoniae, three major pathogens that cause disease at distinct body sites. MUFA synthesis was important for stress and antibiotic tolerance across all three species, while its impact on virulence was species- and context-dependent. Overall, these discoveries provide leads to guide the development of novel therapeutic and/or preventative strategies.
J. L. Baker, Jonah Tang, Mingzhe Guo et al.· Journal of Bacteriology· 0 citations
ABSTRACT Staphylococcus aureus is a globally prevalent gram-positive pathogen that can cause numerous types of infection. Due to host nutritional immunity and iron (Fe) sequestration, S. aureus experiences Fe limitation during infection. To overcome this, S. aureus expresses an arsenal of Fe acquisition systems whose expression is coordinated through the Fe-binding transcriptional regulator, Fur. Here, from a screen to identify S. aureus mutants defective for Fe-restricted growth, we identified several with mutations in perR, encoding a transcriptional regulator involved in resistance to oxidative stress. RNA-seq identified that the most downregulated genes in a perR mutant growing in Fe-restriction are those from the sbn operon that encodes staphyloferrin B biosynthesis. In agreement, perR mutants grew poorly in Fe-deficient media due to deficient staphyloferrin B production. In a subcutaneous model of S. aureus skin infection, S. aureus perR caused significantly smaller lesions, consistent with our finding that this mutant had decreased alpha-hemolysin expression during Fe-restricted growth. These findings are consistent with the hypothesis that PerR acts to fine-tune access to Fe ostensibly to avoid Fe-dependent toxicity. The importance of the PerR function to S. aureus was further highlighted by examination of over 8,000 human bloodstream isolates of S. aureus, showing that the PerR sequence was highly conserved. Together, these findings demonstrate the importance of PerR to S. aureus in providing an additional level of regulation of Fe homeostasis beyond Fur-dependent Fe sensing. IMPORTANCE Staphylococcus aureus is a notoriously antibiotic-resistant human pathogen and has the potential to cause a myriad of potentially life-threatening infections. Understanding the intricacies of S. aureus pathogenesis in the host will underpin the development of novel therapeutic approaches that target bacterial virulence mechanisms rather than essential cellular processes. The significance of our research lies in identifying how S. aureus regulates Fe acquisition in response to environmental signals, providing further insight into nutrient sensing and acquisition at the host–pathogen interface to facilitate the development of therapeutics that may target this process. Staphylococcus aureus is a notoriously antibiotic-resistant human pathogen and has the potential to cause a myriad of potentially life-threatening infections. Understanding the intricacies of S. aureus pathogenesis in the host will underpin the development of novel therapeutic approaches that target bacterial virulence mechanisms rather than essential cellular processes. The significance of our research lies in identifying how S. aureus regulates Fe acquisition in response to environmental signals, providing further insight into nutrient sensing and acquisition at the host–pathogen interface to facilitate the development of therapeutics that may target this process.
Alexander A Sheikh, Ronald S. Flannagan, Nathan J Nicholson et al.· Journal of Bacteriology· 0 citations
The RND efflux pump FemT encoded by SAUSA300_2213 of Staphylococcus aureus USA300 is co-transcribed with femX which has an essential role in synthesizing the Lipid II precursor of peptidoglycan. Anticipating that this arrangement reflects a critical accessory role for femT, we constructed USA300ΔfemT to assess its function. Although growth of USA300ΔfemT in tryptic soy broth (TSB) was not impaired, transcriptomic data revealed a mild cellular stress response, accompanied by reduced expression of ohyA and crt genes involved in fatty acid metabolism and carotenoid lipid synthesis respectively. Accordingly, USA300ΔfemT exhibited impaired growth on exposure to saturated and unsaturated fatty acids, and exposure to subinhibitory 50 µM palmitic acid promoted accumulation of reactive oxygen species, reduced respiratory activity, and altered membrane function and morphology. The transcriptome of cells grown under this condition revealed strongly attenuated expression of ohyA and crt, and several genes required for oxidative and anaerobic respiration, concomitant with strongly enhanced expression of several stress response pathways. Cellular metabolites were also profoundly altered. Finally, lipidomic analysis of USA300ΔfemT exposed to oleic acid revealed increased incorporation of oleic acid into phosphatidylglycerol, accompanied by a significant reduction in undecaprenol C55 lipid carrier, and respiratory quinones MK-7 and MK-8. Our data are consistent with a role for FemT in maintaining cellular lipid homeostasis by promoting efflux of isoprenoid and carotenoid lipids that are prone to oxidative damage, including C55 and menaquinones that undergo cyclic reactions in peptidoglycan synthesis and electron transport. IMPORTANCE The FemT efflux pump of S. aureus is co-expressed in an operon with femX encoding an essential enzyme needed to complete the synthesis of peptidoglycan precursor Lipid II. Although this alluded to a specific role for FemT in supporting peptidoglycan synthesis, our data are instead consistent with a general role in efflux of cellular isoprenoids and carotenoid lipids that are susceptible to oxidation during routine cellular functions. Consequently, S. aureus became strongly dependent on FemT function when exogenous host-derived fatty acids were being actively metabolized. This represents a significant advance in our understanding of the role of an RND efflux pump in supporting routine growth-related functions of S. aureus and exposes a function that could be targeted to impair S. aureus growth on exposure to host-derived fatty acids.
A. Thukral, Camryn Bonn Dunbar, Jamie N Halucha et al.· bioRxiv· 0 citations
Staphylococcus aureus
(
S. aureus
)is an important foodborne pathogen. Host-derived catecholamines released under stress are known to influence bacterial pathogenic processes, including growth, virulence, biofilm formation. However, the role of dopamine in this context remains less well understood, particularly in
S. aureus
. In this study, we investigated the effects of dopamine on
S. aureus
ATCC 25,923 using a combination of phenotypic assays and multi-omics analyses. Dopamine was taken up by the bacteria and was associated with enhanced pathogenic phenotypes, including increased proliferation, toxin production, biofilm formation, motility, adhesion, and multidrug resistance. In a mouse infection experiment, dopamine treatment further increased bacterial colonization and organ invasion. Mechanistically, multi-omics analyses indicated that dopamine activates the SaeRS two-component system and is associated with the upregulation of virulence-related factors, adhesion-associated proteins, and membrane lipid synthesis pathways, along with increased activity in key metabolic processes such as the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. Importantly, deletion of
saeS
markedly attenuated these dopamine-associated effects. Taken together, these findings suggest that dopamine likely influences
S. aureus
pathogenicity primarily through the SaeRS signaling pathway and provide insight into how host stress signals may contribute to bacterial infection.
Ben Xu, Ziyue Wang, Jinmei Chai et al.· BMC Microbiology· 0 citations
Toxin-antitoxin (TA) systems are bacteria-specific components involved in maintaining mobile genetic elements that may carry antibiotic resistance determinants (ARDs), among other functions. PemIK-Sa1 is a plasmid-encoded TA system found in Staphylococcus aureus, a dangerous pathogen affecting humans and animals. The PemK-Sa1 toxin is a sequence-specific ribonuclease inhibited by its cognate antitoxin, PemI-Sa1. Using recombinant multidrug-resistant strains, we demonstrated that expression of the toxin reduces resistance to antibiotics from various classes, including β-lactams, fluoroquinolones, aminoglycosides, and chloramphenicol. Transcriptomics revealed that, in addition to downregulation of genes encoding ARDs, nearly one-third of the staphylococcal transcriptome is altered. Furthermore, proteomic analysis revealed that toxin expression results in the downregulation of several proteins involved in nucleotide biosynthesis, carbohydrate metabolism, and energy production. This indicates parallel mechanisms in which the toxin not only degrades ARD transcripts, thereby directly impacting their function, but also alters the expression of genes encoding proteins crucial to essential cell processes. The ability to reduce resistance to a broad range of antibiotics makes the PemK-Sa1 toxin a promising tool for combating multidrug-resistant bacteria through the artificial activation of the PemIK-Sa1 TA system.
Emilia Bonar, Kinga Chlebicka, Michał Bukowski et al.· Frontiers in Microbiology· 0 citations
ABSTRACT Iron acquisition is a crucial step for bacterial survival that shapes bacterial fitness and ecological interactions within microbial communities. Pseudomonas aeruginosa, an opportunistic clinical and environmental bacterium, relies on high-affinity siderophores such as pyoverdines to scavenge iron. Understanding these pathways provides vital insights into siderophore specificity, bacterial resource competition, and iron metabolism in bacteria. Here, we report vacidobactin A (VacA), a siderophore produced by the soil bacterium Variovorax paradoxus, identified through a screen of natural product extracts targeting a clinical multi-drug-resistant strain of P. aeruginosa. Rather than functioning as a direct antimicrobial agent, VacA impairs the growth of P. aeruginosa by imposing iron starvation. This is observed exclusively in strains that are unable to produce pyoverdine, their native siderophore. To determine whether VacA-mediated inhibition resulted from restricted access to iron, we heterologously expressed a TonB-dependent transporter from V. paradoxus in a pyoverdine- and pyochelin-deficient P. aeruginosa strain. Transporter expression enabled utilization of VacA-bound iron and restored growth, demonstrating that the antagonistic effect of VacA is governed by selective siderophore recognition and uptake rather than iron sequestration alone. Additionally, VacA synergized with thiostrepton, which hijacks pyoverdine receptors to enter the cell and inhibit protein synthesis. This investigation demonstrates how environmental microorganisms exploit siderophore specificity to compete for iron and establish antagonistic relationships within microbial communities. IMPORTANCE Iron acquisition is fundamental to bacterial survival and shapes ecological interactions within microbial communities, yet the mechanistic principles governing siderophore specificity and iron competition remain incompletely understood. Here, we demonstrate that vacidobactin A, a siderophore produced by Variovorax paradoxus, suppresses P. aeruginosa growth by limiting iron availability, particularly in strains deficient in pyoverdine production. By demonstrating that heterologous expression of a TonB-dependent transporter restores iron utilization from vacidobactin A, we establish that siderophore-mediated antagonism is governed by selective recognition and uptake pathways. Furthermore, the synergy between vacidobactin A and thiostrepton illustrates how siderophore systems integrate with other cellular vulnerabilities. These findings illuminate fundamental principles of bacterial resource competition and highlight how environmental microorganisms exploit iron metabolism as a competitive strategy, advancing our understanding of microbial community dynamics and bacterial physiology. Iron acquisition is fundamental to bacterial survival and shapes ecological interactions within microbial communities, yet the mechanistic principles governing siderophore specificity and iron competition remain incompletely understood. Here, we demonstrate that vacidobactin A, a siderophore produced by Variovorax paradoxus, suppresses P. aeruginosa growth by limiting iron availability, particularly in strains deficient in pyoverdine production. By demonstrating that heterologous expression of a TonB-dependent transporter restores iron utilization from vacidobactin A, we establish that siderophore-mediated antagonism is governed by selective recognition and uptake pathways. Furthermore, the synergy between vacidobactin A and thiostrepton illustrates how siderophore systems integrate with other cellular vulnerabilities. These findings illuminate fundamental principles of bacterial resource competition and highlight how environmental microorganisms exploit iron metabolism as a competitive strategy, advancing our understanding of microbial community dynamics and bacterial physiology.
Manpreet Kaur, Derek C. K. Chan, Hodan Wardere et al.· Microbiology spectrum· 0 citations