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Dietary Restriction of Caenorhabditis elegans by Axenic Culture Reflects Nutritional Requirement for Constituents Provided by Metabolically Active Microbes

¹ Department of Biology, University of Ghent, Belgium.
² Centre for Research on Ageing, Department of Biology, University College London, United Kingdom.
³ Department of Subatomic and Radiation Physics, University of Ghent, Belgium.

Address correspondence to Jacques R. Vanfleteren, PhD, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, 9000 Ghent, Belgium. E-mail: jacques.vanfleteren{at}ugent.be

In Caenorhabditis elegans, several manipulations that affect nutrition slow development, reduce fecundity, and increase life span. These are viewed as dietary restriction (DR) and include culture in semidefined, nutrient-rich liquid medium that is axenic (i.e., there is no microbial food source). Here we describe convenient ways to exert DR by culture on agar plates containing axenic medium. We used these to explore whether effects of axenic culture really reflect DR. Our results imply that major nutrient components of axenic medium, and overall caloric content, are not limiting for life span. However, adding growth-arrested Escherichia coli as an additional food source rescued the effects of axenic culture. We then sought to identify the component of E. coli that is critical for normal C. elegans nutrition using add-back experiments. Our results suggest that C. elegans has a nutritional requirement for live, metabolically active microbes or, possibly, an unidentified, heat-labile, nonsoluble component present in live microbes.

Key Words: Dietary restriction • Caenorhabditis elegans • Escherichia coli • Aging • Axenic culture