For information about UWM’s fall semester plans, visit the Fall 2020 Reopening website.
Our laboratory is interested in understanding the mechanisms by which bacteria adapt to different host environments. We study as a model system Xenorhabdus nematophila, a motile gram-negative bacterium that engages in both mutualistic and pathogenic host interactions. Xenorhabdus forms a species-specific mutualistic association with the insect-invading nematode, Steinernema carpocapsae. The nematode enters insect hosts and X. nematophila is released from an intestinal vesicle into the insect's body cavity (hemocoel) where it functions as a pathogen. Contraction of the esophagus of the nematode stimulates the forward movement of Xenorhabdus out of the vesicle through a connecting structure that allows the bacteria to enter the intestine and ultimately leave the nematode via the anus. In the hemocoel, Xenorhabdus initially colonizes the connective tissue surrounding the anterior midgut of the host insect. The bacteria proliferate in the insect cadaver reaching high cell densities at which point they produce diverse exoenzymes and antibiotics. The bacteria themselves, as well as the macromolecular degradation they stimulate, provide a nutrient base suitable for nematode reproduction. After several cycles of sexual reproduction the nematodes develop into a dauer juvenile stage that possesses the specialized intestinal vesicle that Xenorhabdus colonizes by a monoclonal process.