Biology subjects

Radka, C. D.

Publications and source records attributed to Radka, C. D..

3 recordsLinked to original sources

bioRxiv2025

Mechanisms of 10-Hydroxyoctadecanoic acid resistance in Streptococcus pneumoniae

Profiles of human nasal colonization consistently demonstrate that Staphylococcus aureus and Streptococcus pneumoniae can co-exist in the nasopharynx. Several studies have demonstrated the antagonist relationship between the two organisms via several molecular mechanisms including competition for nutrients as well as via direct killing by hydrogen peroxide. During nasal colonization, the pneumococcus is in direct contact with the fatty acid h18:0, which is released into the extracellular environment by S. aureus. We report that h18:0 is specifically toxic to the pneumococcus amongst the pathogenic streptococci, providing a unique mechanism for interspecies competition during colonization. Exposure of cells to h18:0 revealed that S. pneumoniae could rapidly adapt to and overcome the observed toxicity. Whole genome analysis revealed the mechanism underlying this resistance being linked to a truncation of a glycosyltransferase in the capsule biosynthesis locus and a genomic inversion in the phase variation locus, leading to altered cell surface charge and membrane lipid composition. These physiological differences in the resistant isolates may aid in repelling toxic, charged fatty acids such as h18:0 from the cell membrane. IMPORTANCEThe pneumococcus and S. aureus are two of the most well-characterized residents of the human nasopharynx; yet much remains unknown regarding how the two bacteria interact. Here, we describe the potential of S. aureus-produced h18:0, whose function and biological impact are still being described, to act as an inter-species competition molecule against S. pneumoniae, and how the pneumococcus can adapt to overcome its toxicity.

microbiology↗

bioRxiv2025

Isoleucine binding and regulation of Escherichia coli and Staphylococcus aureus threonine dehydratase (IlvA)

In Staphylococcus aureus, the branched-chain amino acid biosynthetic pathway provides essential intermediates for membrane biosynthesis. Threonine deaminase (IlvA) is the first enzyme in the pathway, and isoleucine feedback-regulates the enzyme in Escherichia coli. These studies on E. coli IlvA (EcIlvA) introduced the concept of allosteric regulation. To investigate the regulation of S. aureus IlvA (SaIlvA), we first conducted additional studies on EcIlvA. The previously determined crystal structure of EcIlvA revealed a tetrameric assembly of protomers, each with catalytic and regulatory domains, but the structural basis of isoleucine regulation was not characterized. Here, we present the crystal structure of the EcIlvA regulatory domain bound to isoleucine, which reveals the isoleucine binding site and conformational changes that initiate at Phe352 and propagate 23 [A] across the domain. This suggests an allosteric pathway that extends to the active site of the adjacent protomer, mediating regulation across the protomer-protomer interface. The EcIlvA(F352A) mutant binds isoleucine but is feedback-resistant due to the absence of the initiating Phe352. In contrast, SaIlvA is not feedback-regulated by isoleucine and does not bind it. The structure of the SaIlvA regulatory domain reveals a different organization that lacks the isoleucine binding site. Other potential allosteric inhibitors of SaIlvA, including phospholipid intermediates, do not affect enzyme activity. We propose that the absence of feedback inhibition in SaIlvA is due to its role in membrane biosynthesis. These findings enhance our understanding of IlvAs allosteric regulation and offer opportunities for engineering feedback-resistant IlvA variants for biotechnological use.

microbiology↗

bioRxiv2023

Vaginal Lactobacillus fatty acid response mechanisms reveal a novel strategy for bacterial vaginosis treatment

Bacterial vaginosis (BV), a common syndrome characterized by Lactobacillus-deficient vaginal microbiota, is associated with adverse health outcomes. BV often recurs after standard antibiotic therapy in part because antibiotics promote microbiota dominance by Lactobacillus iners instead of Lactobacillus crispatus, which has more beneficial health associations. Strategies to promote L. crispatus and inhibit L. iners are thus needed. We show that oleic acid (OA) and similar long-chain fatty acids simultaneously inhibit L. iners and enhance L. crispatus growth. These phenotypes require OA-inducible genes conserved in L. crispatus and related species, including an oleate hydratase (ohyA) and putative fatty acid efflux pump (farE). FarE mediates OA resistance, while OhyA is robustly active in the human vaginal microbiota and sequesters OA in a derivative form that only ohyA-harboring organisms can exploit. Finally, OA promotes L. crispatus dominance more effectively than antibiotics in an in vitro model of BV, suggesting a novel approach for treatment.

microbiology↗