Masters Thesis

Horizontal and vertical transmission of a Pantoea sp. in Culex sp.

Mosquitoes serve as vectors for several life-threatening pathogens such as Plasmodium spp. that cause malaria and Dengue viruses that cause dengue hemorrhagic fever. Control of mosquito populations through insecticide use, human-mosquito barriers such as the use of bed nets, and control of standing water, such as areas where rainwater has collected, collectively work to decrease transmission of pathogens. None, however, continue to work to keep disease incidence at acceptable levels. Novel approaches, such as paratransgenesis are needed that work specifically to interrupt pathogen transmission. Paratransgenesis employs symbionts of insect vectors to work against the pathogens they carry. In order to take this approach a candidate symbiont must reside in the insect where the pathogen also resides, the symbiont has to be safe for use, and amenable to genetic transformation. For mosquito species, Pantoea agglomerans is being considered for use because it satisfies all of these criteria. What isn’t known about P. agglomerans is how mosquitoes specifically acquire this bacterium, although given that this bacterium is a typical inhabitant of the environment it is likely they acquire it horizontally through feeding and/or exposure to natural waters. It is possible that they pass the bacteria to their offspring directly by vertical transmission routes. The goal of my research is to determine means of symbiont acquisition in Culex pipiens, the Northern House Mosquito. I chose C. pipiens as a model organism due to its ease of rearing in a laboratory setting. My research involved monitoring the fate of P. agglomerans that contained a fluorescent marker that was ingested by laboratory-reared adult male and female C. pipiens to verify horizontal transmission and determine if vertical transmission occurs. I used a combination of standard microbiological techniques and tests in conjunction with fluorescent microscopy. I found that both male and female C. pipiens acquire P. agglomerans horizontally and that females pass the bacteria to their offspring. To my knowledge, this is the first report of vertical transmission in C. pipiens. I also found that identification of P. agglomerans using standard biochemical tests and databases can be unreliable which can impact its use in the field raising risk assessment and environmental impact questions.

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