The Role of PF Phage in Pseudomonas aeruginosa Cheater Populations

Pseudomonas aeruginosa (Pa) is a bacterial pathogen that causes millions of hospital-acquired infections each year. Pa often forms a biofilm (bacteria encased in a self-produced protective matrix) at sites of infection. To build a biofilm, Pauses a cell density-dependent mechanism called quorum sensing (QS) to coordinate gene expression. Many quorum-regulated products are secreted into the extracellular space and are considered public goods (products that can be used by any member of the microbial community). Some members of the biofilm community, however, cheat and do not produce public goods but, continue to consume them. These individuals are known as cheaters . High levels of cheaters in a microbial population can result in community collapse. Thus, the number of cheaters needs to be regulated in microbial communities. We have discovered that a bacteriophage (a virus that infects bacteria) is regulated by quorum sensing-when quorum sensing is disabled, the bacteriophage replicates and slows the growth of P. aeruginosa. Our previous work indicates that these bacteriophage play key roles in infection pathogenesis. We hypothesize that these bacteriophage introduce a selective pressure against cheaters. To test this hypothesis, we will measure the abundance of cheaters in bacterial populations that either do or do not contain bacteriophage. Cheaters will be identified using selective growth media and the abundance of cheaters will be measured over time. We predict that bacterial populations without bacteriophage will have a higher percentage of cheaters compared to bacterial populations with bacteriophage. Understanding how cheaters are regulated in bacterial populations may reveal new therapeutic strategies that promote cheating, promoting a tragedy of the commons within microbial communities that cause disease