Experimentally Evolved Staphylococcus aureus Survives in the Presence of Pseudomonas aeruginosa by Acquiring Mutations in the Amino Acid Transporter, GltT.

• Type of Material: Article
• Authors: Ashley M. Alexander, Emory University; Justin M. Luu, Emory University; Vishnu Raghuram, Emory University; Giulia Bottacin, University of Basel; Simon van Vliet, University of Lausanne; Timothy Read, Emory University; Joanna Goldberg, Emory University
• Language: English
• Date: 2023-07-24
• Publisher: NIH
• Publication Version: Preprint (Prior to Peer Review)
• Copyright Statement: The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1101/2023.07.24.550428
• Title of Journal or Parent Work: bioRxiv
• Grant/Funding Information: This work was supported in part with grants for the National Institutes of Health (R21 AI148847) and the US Cystic Fibrosis Foundation (GOLDBE19I0) to JBG. Research reported in this publication was supported in part by National Institute of Allergy and Infectious Diseases of the National Institutes of Health (T32AI138952), and Emory University and the Infectious Disease Across Scales Training Program (IDASTP) (AMA). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health, Emory University or IDASTP.; GB and SVV were supported by an Ambizione grant from the Swiss National Science Foundation (grant no. PZ00P3_202186) and by the University of Basel.
• Keywords: cystic fibrosis; Staphylococcus aureus; amino acid metabolism; interspecies competition; Pseudomonas aeruginosa; Experimental Evolution
• Research Categories: Health Sciences, Pathology

Abstract

UNLABELLED: Staphylococcus aureus and Pseudomonas aeruginosa are the most common bacterial pathogens isolated from cystic fibrosis (CF) related lung infections. When both of these opportunistic pathogens are found in a coinfection, CF patients tend to have higher rates of pulmonary exacerbations and experience a more rapid decrease in lung function. When cultured together under standard laboratory conditions, it is often observed that P. aeruginosa effectively inhibits S. aureus growth. Previous work from our group revealed that S. aureus from CF infections have isolate-specific survival capabilities when cocultured with P. aeruginosa . In this study, we designed a serial transfer evolution experiment to identify mutations that allow S. aureus to adapt to the presence of P. aeruginosa . Using S. aureus USA300 JE2 as our ancestral strain, populations of S. aureus were repeatedly cocultured with fresh P. aeruginosa strain, PAO1. After 8 coculture periods, S. aureus populations that survived better in the presence of PAO1 were observed. We found two independent mutations in the highly conserved S. aureus aspartate transporter, gltT , that were unique to evolved P. aeruginosa -tolerant isolates. Subsequent phenotypic testing demonstrated that gltT mutants have reduced uptake of glutamate and outcompete wild-type S. aureus when glutamate is absent from chemically-defined media. These findings together demonstrate that the presence of P. aeruginosa exerts selective pressure on S. aureus to alter its uptake and metabolism of key amino acids when the two bacteria are cultured together. IMPORTANCE: Staphylococcus aureus and Pseudomonas aeruginosa are the two most common bacterial pathogens that infect people with the genetic disease, cystic fibrosis (CF). They are often found together in CF-associated polymicrobial infections that are associated with worse patient prognosis. Understanding how these very different opportunistic pathogens influence each other in a shared environment is pertinent to improving the treatment of polymicrobial infections. While much attention has been brought to the interspecific interactions between S. aureus and P. aeruginosa, few studies have used experimental evolution methods to identify determinants of their competition and coexistence. Here, we use a serial transfer experimental evolution approach and identified a single genetic change associated with improved survival of S. aureus in the presence of P. aeruginosa. Our findings implicate metabolism of shared resources as an important factor in S. aureus's ability to survive in the presence of P. aeruginosa .