Thesis Title

A Systematic Approach to Understand the Bacterially-Derived Determinants of Growth and Aging in Caenorhabditis Elegans

Graduation Date

Spring 2011

Document Type

Master's Thesis

Degree Name

Master of Science

Program Name

Biological Science

Program Director

Kiowa Bower, PhD

First Reader

Pankaj Kapahi, PhD

Second Reader

Shelia Johnson-Brousseau, PhD

Abstract

Emerging studies have demonstrated that biological responses are greatly influenced by dietary intake. Dietary restriction (DR), or reduction of dietary intake without starvation, has been shown to significantly extend longevity in a number of species and has been implicated in slowing down the onset of age-related diseases. However individual nutrient mediators that affect DR-dependent lifespan extension have yet to be found. Studies altering the Escherichia coli (E. coli) food source fed to Caenorhabditis elegans (C. elegans] have demonstrated that significant changes in their metabolic profiles and lifespan are affected11-3. Despite these studies, a systematic understanding of the bacterial contribution in development and aging has yet to be performed. Therefore, I carried out a systematic screen utilizing the Keio Collection of single open reading frame (ORF) knockout E. coli mutants to determine the role £ coli Plays in affecting development and aging in C. elegans. In particular, I attempted to sensitize the screen in an rsks-l-dependent manner by feeding individual Keio bacterial mutants to rsks-1 worms that carry a mutation in the ribosomal s6 kinase (rsks-1), a downstream target of the major nutrient sensor Target of Rapamycin (TOR). After screening 3,985 genes from the Keio library, I found 180 E. coli candidate genes that delayed C. elegans development. These were retested in a wild-type (N2) C elegans background and 74 appeared to cause an rsks-1 -specific developmental delay. To better understand the link between development and adult lifespan, I characterized 30 of the 74 mutant E. coli genes that were well annotated and represented a class of genes identified by lifespan assays. Of these 30 mutants, 9 showed significant lifespan extension in an rsks-l-specific manner. One such mutant, dnaK, is the E. coli heat shock protein 70 (HSP70), a chaperone important for repairing misfolded or unfolded proteins that acts by binding to hydrophobic sequences, preventing irreversible aggregation4. Interestingly, when fed to C. elegans, this aggregation-sensitive mutant delayed normal C. elegans development and significantly extended its lifespan compared to worms feedK12 control E. coli. When used as the primary food source, the other eight Keio E. coli candidate genes investigated also demonstrated variable degrees of delayed development and lifespan extension in C elegans. Talen together, this suggests that mutations in an organism’s food source can produce changes in C elegans development that also alter lifespan and may aid in understanding how gut microbes alter a host’s metabolism. Furthermore, it can also serve as a novel tool in discovering micronutrients important for growth, aging, and metabolism in C. elegans.

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