All ETDs from UAB

Advisory Committee Chair

Creg Darby

Advisory Committee Members

David M Bedwell

Michael A Miller

Julian C Rayner

Thomas R Unnasch

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine


The closely related bacterial species Xenorhabdus nematophila, Yersinia pestis and Y. pseudotuberculosis make biofilms capable of adhering to the head of the model nematode Caenorhabditis elegans. Y. pestis uses biofilms to block the digestive tract of its vector, the flea, in order to enhance its efficiency of transmission. I investigated the role of biofilms in X. nematophila and found that, like its Yersinia sp. counterparts, production of biofilm requires a four-gene operon: hmsHFRS. X. nematophila is an insect pathogen and an obligate symbiont of the nematode Steinernema carpocapsae. However, an X. nematophila hmsH mutant that failed to make biofilms on C. elegans had no detectable defect in symbiotic association with S. carpocapsae, nor was virulence reduced against the insect Manduca sexta. Using the biofilm attachment phenotype, I identified several host genes involved with the synthesis of the outer surface of C. elegans. These genes fall into several categories, including the TGF-β pathway and nuclear hormone receptors. Furthermore, three novel genes were identified in a screen for biofilm absent on the head phenotypes (Bah). I cloned and characterized the gene bah-1. This gene encodes a member of a large protein family, known as DUF23s, which has 67 members in C. elegans. Besides resistance to biofilm, bah-1 mutants also show an increase in cuticle fragility. In addition, RNA interference knock-down of multiple DUF23 genes produces a strong surface disruption, suggesting that DUF23 proteins function together to maintain cuticle integrity.



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