Biofilms are communities of surface-associated microbes encased in slime that are naturally tolerant to antimicrobial treatment. It is estimated that 80% of chronic infections are caused by biofilms. One component of the slime layer, or the extracellular polymeric substance (EPS) of biofilms that has yet to be elucidated in depth are outer membrane vesicles (OMVs). These 50-300 nm particles are involved in transporting a wide variety of contents including virulence factors, degradative enzymes, plasmid DNA, small RNAs, and communication molecules. However, these functions were studied in bacteria living in a free-swimming planktonic condition, which gives us a misinformed view of bacterial pathogenesis. If we are to better understand how bacteria exist in a chronic infection, we must study OMVs in a biofilm context. This study specifically analyzed Pseudomonas aeruginosa because it is a model organism for biofilm studies, OMV studies, and because OMV formation in this bacterium is controlled by the Pseudomonas Quinolone Signal (PQS). This allowed us to investigate how OMV deficient biofilms differ from wild type biofilms by using PQS mutant strains. Our results show that OMV formation in biofilms is primarily driven by PQS, however there also exists a subpopulation of vesicles that are produced independently of PQS. Analysis of PQS mutants during biofilm formation suggests that PQS and OMVs are not involved in the attachment of P. aeruginosa to a surface, but they are involved in the dispersion stage of biofilm formation – when bacteria degrade the biofilm EPS and swim away to colonize another surface. Further analyses show that OMVs are capable of associating with pre-formed biofilms and contain enzymes that can degrade biofilm EPS. Therefore, we propose that in P. aeruginosa biofilms, PQS induces OMV formation resulting in the release of enzymes within the OMVs that degrade the EPS and promote biofilm dispersion. This work provides insight into how OMVs are produced and used by bacteria living as a biofilm.
|Advisor:||Schertzer, Jeffrey W.|
|Commitee:||Davies, David G., Marques, Cláudia N. H., Chiarot, Paul R.|
|School:||State University of New York at Binghamton|
|School Location:||United States -- New York|
|Source:||DAI-B 81/2(E), Dissertation Abstracts International|
|Keywords:||Biofilms, Outer membrane vesicles, Pseudomonas quinolone signal|
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