Analysis of the interaction of Francisella tularensis LVS and Legionella pneumophila biofilms with components of the aquatic environment

Biofilms are complex communities of organisms enclosed in a matrix (EPS) composed of polysaccharides, proteins and DNA. Biofilms are the base of the aquatic ecosystem and interact with the biotic as well as the abiotic components in the environment. Biofilms interact with biotic components of the environment such as protozoa and aquatic invertebrates. In this project, the biotic interactions of Francisella tularensis LVS biofilms are studied in relation to the mosquito larvae of Culex quinquefasciatus. F. tularensis is the causative agent of tularemia and is transmitted by ticks, deer flies, and mosquitoes. Mosquitoes are believed to play a role in transmission of tularemia in Europe. Hence, using C. quinquefasciatus as a model system, we wanted to test the effects of acquisition of F. tularensis LVS biofilms on the larvae. Our results demonstrate that F. tularensis LVS can form biofilms in media as well as persist in simulated natural water. The persistence of the bacteria is important as the bacteria can now serve as food source for the aquatic mosquito larvae. The results also show uptake and localization of F. tularensis LVS within the mosquito larvae suggesting a potential mechanism for bacterial persistence in the environment. The data further shows effects of F. tularensis LVS ingestion on mosquito life history traits, including fecundity.;Along with the biotic components in the environment, the biofilms also interact with abiotic components that primarily include anthropogenic sources such as metal contaminants, and release of nanoparticles in the aquatic system. Naturally occurring nanoparticles are generated due to mineral weathering and occur ubiquitously. Thus, they are likely to interact with bacterial biofilms in the aquatic environment. In this study, we investigated the abiotic interactions of L. pneumophila biofilms by studying their interaction with nanoparticles and biocides. L. pneumophila is the causative agent of Legionnaires' Disease and affects the elderly and immune-compromised individuals. Legionella biofilms in industrial cooling towers pose a serious health risk due to generation of aerosols that can contain bacteria. Previously, our lab showed a change in the morphology of Legionella biofilms upon exposure to 18 nm gold particles. We hypothesized that combination of nanoparticle exposure followed by biocide treatment will significantly reduce the biomass of the biofilms. Upon exposure to nanoparticles followed by bleach, a significant reduction in the biomass of the biofilms was observed. The results also suggest that, although not significantly different, the combination of nanoparticles and chlorine dioxide delays the regrowth of the biofilm. Studying the impact of both biotic and abiotic interactions with biofilms is vital in understanding persistence and dissemination strategies of infectious bacteria.