Date of Award


Document Type


Degree Name

Master of Science (MS)


School of Biological Sciences

First Advisor

Jan-Ulrik Dahl


Due to their frequent coexistence in many polymicrobial infections, including in patients with wounds and cystic fibrosis, recent studies have started to investigate how the opportunistic pathogens Pseudomonas aeruginosa and Staphylococcus aureus interact with each other. P. aeruginosa rapidly outcompetes S. aureus under in vitro co-cultivation conditions, which is mediated by several of P. aeruginosa’s virulence factors. Here, we report that polyphosphate (polyP), an efficient stress defense system and virulence factor in P. aeruginosa, plays a role for the pathogen’s ability to inhibit and kill S. aureus in a contact-independent manner. We show that P. aeruginosa cells characterized by low polyP levels are less detrimental to S. aureus growth and survival while the gram-positive pathogen is significantly more susceptible when co-cultivated with P. aeruginosa cells characterized by high levels of polyP. We show that this polyP-dependent phenotype could be a direct effect by the biopolymer, as polyP causes significant damage to the S. aureus cell envelope. However, more likely is that polyP acts indirectly through regulating one of P. aeruginosa’s virulence factors, pyocyanin. We show that pyocyanin production in P. aeruginosa harms S. aureus through membrane damage and the generation of reactive oxygen species in a polyP-dependent manner, both of which can contribute to the antimicrobial effect of the phenazine molecule. In summary, our study adds a new component to the list of biomolecules that the gram-negative pathogen P. aeruginosa generates to compete with S. aureus for resources.


Imported from Shah_ilstu_0092N_12501.pdf


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