Author ORCID Identifier

https://orcid.org/0000-0003-3277-2948

Date of Award

Winter 11-24-2025

Document Type

Thesis (Ph.D.)

Department or Program

Microbiology and Immunology

First Advisor

George O'Toole

Abstract

Cystic fibrosis (CF) airway microbial communities are complex ecosystems where interspecies interactions influence pathogen survival and disease progression. We leverage a CF-relevant in vitro four-species model composed of Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus sanguinis, and Prevotella melaninogenica, alongside a microbiome dataset with over 4,000 respiratory samples from publicly available sequencing data of CF patient samples, to explore the dynamics of microbial interactions in CF. On a broader scale, we performed microbial network analysis to examine how the latest modulator therapy, elexacaftor/tezacaftor/ivacaftor (ETI), might influence CF microbial communities. Our analysis revealed a reduction in node connections and positive correlations between the most abundant genera following ETI treatment, which predicts fragmentation of microbial communities across different regions of the respiratory tract. By focusing on the interactions between P. melaninogenica, P. aeruginosa, and S. sanguinis, we found that P. melaninogenica, which cannot survive alone in mucin-containing artificial sputum medium (ASM), relies on P. aeruginosa through a dynamic mechanism of metabolic cross-feeding. We posit that P. melaninogenica ferments mucin into malonate and propionate, which P. aeruginosa respectively metabolizes into acetate and succinate, and provides these metabolites back to P. melaninogenica to support its growth in ASM. A genetic screen identified P. aeruginosa mutants in pathways responsible for propionate and malonate metabolism, which lead to the significant reduction of P. melaninogenica recovery in co-culture. Supplementing these co-cultures with acetate and succinate, rescued the growth of P. melaninogenica in co-culture. In addition to metabolic support, we observed that P. aeruginosa also shields P. melaninogenica from antagonism by S. sanguinis, which consistently inhibits P. melaninogenica growth in co-cultures. We identified reactive nitrogen stress as one mechanism through which S. sanguinis exerts its antagonistic effects. Analyzing these specific interactions will help us generate strategies that can modulate microbial communities to the benefit of pwCF, especially given the observed changes in community structures following ETI therapy.

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