Deciphering the unique and independent roles of the alpha phenol soluble modulin (APSM) peptides and APSM transcript in staphylococcus aureus

The National Institute of Allergy and Infectious Diseases awarded Ohio University $563,035 on September 1, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855) to investigate the distinct biological functions of alpha phenol soluble modulin (APSM) peptides and the regulatory role of the APSM transcript in Staphylococcus aureus pathogenesis.

The research addresses gaps in understanding how individual APSM peptides contribute to specific bacterial phenotypes, including cell lysis, biofilm development, extracellular vesicle production, immune activation, and virulence. Prior studies used complete APSM knockout mutants that eliminated production of all four peptides simultaneously; this project will employ individual mutant strains to determine which phenotypes associate with specific peptides. The second aim investigates a novel hypothesis that the APSM transcript functions as a regulatory RNA in addition to encoding the peptides themselves, supported by preliminary data and prior studies implicating the APSM locus in gene regulation.

The work is performed in Ohio and runs through August 31, 2029. This project grant supports research in a fundamental area relevant to community-acquired methicillin-resistant S. aureus (CA-MRSA) strains, particularly the highly virulent USA300 lineage.

Abstract

Staphylococcus aureus is both a commensal of humans and a highly dangerous bacterial pathogen. S. Aureus pathogenesis is mediated by a large repertoire of secreted and cell wall-associated virulence factors, including several potent cytolytic peptides called alpha phenol soluble modulins (ΑPSMS). ΑPSMS are amphipathic, alpha helical peptides, approximately 22 amino acids in size, and have been the focus of intense study in recent years. They have been implicated in contributing to the high virulence potential of community-acquired methicillin resistant S. Aureus (CA-MRSA) strains, in particular those of the USA300 lineage. While the role of ΑPSMS in S. Aureus infection has been extensively investigated, significant gaps exist in our understanding of their specific role(S) in the bacterial cell. Two key gaps in knowledge will be investigated in this proposal, which we believe will lead to a paradigm shift in how the αpsm transcript and the encoded peptides are perceived. Aim 1 will investigate the specific biological function of each individual αpsm peptide. Numerous phenotypes, including cell lysis, biofilm development, EV production, immune activation, and virulence have been linked to αpsm activity, however the specific contribution of each individual peptide to each phenotype is unknown. All previous studies into αpsm function have utilized complete psmα knockout mutants that abrogate production of all four peptides. We will utilize individual mutants to determine which phenotypes are associated with which peptide(S). Aim 2 will investigate a novel hypothesis that the psmα transcript, in addition to encoding the αpsm peptides, is also a regulatory RNA. To support this novel hypothesis, we provide compelling preliminary data and cite previous studies implicating the αpsm locus in regulation of gene expression by an unknown mechanism. The proposed work is highly interdisciplinary and combines genetic, biochemical, molecular biology, bioinformatics, and in vivo approaches to address major questions regarding the role and regulation of the ΑPSMS. The results are expected to substantially enhance our understanding of the distinct biological functions of individual ΑPSMS and, for the first time, reveal that the psmα transcript has regulatory activity.