Identification of attractive odorants released by preferred bacterial food found in the natural habitats of C. elegans.

Food choice is critical for survival because organisms must choose food that is edible and nutritious and avoid pathogenic food. Many organisms, including the nematode C. elegans, use olfaction to detect and distinguish among food sources. C. elegans exhibits innate preferences for the odors of different bacterial species. However, little is known about the preferences of C. elegans for bacterial strains isolated from their natural environment as well as the attractive volatile compounds released by preferred natural bacteria isolates. We tested food odor preferences of C. elegans for non-pathogenic bacteria found in their natural habitats. We found that C. elegans showed a preference for the odor of six of the eight tested bacterial isolates over its standard food source, E. coli HB101. Using solid-phase microextraction and gas chromatography coupled with mass spectrometry, we found that four of six attractive bacterial isolates (Alcaligenes sp. JUb4, Providenica sp. JUb5, Providencia sp. JUb39, and Flavobacteria sp. JUb43) released isoamyl alcohol, a well-studied C. elegans attractant, while both non-attractive isolates (Raoultella sp. JUb38 and Acinetobacter sp. JUb68) released very low or non-detectable amounts of isoamyl alcohol. In conclusion, we find that isoamyl alcohol is likely an ethologically relevant odor that is released by some attractive bacterial isolates in the natural environment of C. elegans.

Modeling the role of negative cooperativity in metabolic regulation and homeostasis.

A significant proportion of enzymes display cooperativity in binding ligand molecules, and such effects have an important impact on metabolic regulation. This is easiest to understand in the case of positive cooperativity. Sharp responses to changes in metabolite concentrations can allow organisms to better respond to environmental changes and maintain metabolic homeostasis. However, despite the fact that negative cooperativity is almost as common as positive, it has been harder to imagine what advantages it provides. Here we use computational models to explore the utility of negative cooperativity in one particular context: that of an inhibitor binding to an enzyme. We identify several factors which may contribute, and show that acting together they can make negative cooperativity advantageous.