Rosser_thesis.pdf

Serratia marcescens is a bacterium with a ubiquitous environmental distribution and the ability to cause opportunistic infections. This research explores three different group behaviors in S. marcescens. These are biofilm formation, microbial hitchhiking, and responses to cannabinoid-induced stress. To study biofilm development, we used a crystal violet assay to measure biofilm and compared that to the bacterial growth of those cultures. We looked at the role of nutrients and temperature in biofilm produced by S. marcescens and tested four S. marcescens strains. We found that there were differences in the ratio of biofilm to growth when S. marcescens was grown in different media. The exact relationship between temperature and media composition requires more information than could be attained from these studies. Next, we wanted to investigate whether S. marcescens could also utilize movement of other, more highly motile species of bacteria through a process called microbial hitchhiking. S. marcescens was grown with a highly motile Paenibacillus sp. isolate. S. marcescens was tracked by the red pigment that it produces. It was observed that S. marcescens consistently spread farther across a surface when it was co-cultured with Paenibacillus sp. than when grown alone. This was repeated with three other S. marcescens strains and three different species of Paenibacillus. Hitchhiking behavior was observed in all cases. To understand the mechanism by which S. marcescens hitchhikes on Paenibacillus spp., a S. marcescens flagellar mutant was used. Even in the absence of a flagellum, S. marcescens was still able to hitchhike implying that another mechanism must be involved. Finally, we evaluated the response of S. marcescens to cannabidiol (CBD) a phytocannabinoid with antimicrobial and antibiofilm properties, though it has limited potency against Gram-negative bacteria like S. marcescens. We found that CBD did not kill S. marcescens nor did it affect its biofilm development. Interestingly, S. marcescens cultures showed enhanced pigment production in response to high-dose CBD exposure compared to vehicle controls. This response was also observed with exposure to three additional phytocannabinoids. Results from these studies add to our understanding of how S. marcescens can access new areas and persist in a broad range of environments.