Bite size of Caenorhabditis elegans regulates feeding, satiety and development on yeast diet

Abstract

In the wild, the soil dwelling nematode Caenorhabditis elegans primarily feeds on microbes which are abundant in rotting vegetation. Recent published studies showthat several Gram-positive and Gram-negative bacterial populations predominantly constitutes the C. elegans gut microbiome but surprisingly lack any yeast species. Here, we show that C. elegans display low satiety on yeast diet of Cryptococcus neoformans, C. laurentii or S. cerevisiae. We found that average size of budding yeast cells is much larger than E. coli cells. Yeast cells also cause pharyngeal obstruction, diminished feeding, and lower level of neutral lipids in adult C. elegans. Using scanning electron microscopy, we show that the mouth size of C. elegans larvae is smaller than average yeast cell. The larvae have no detectable yeast in their alimentary canal and they undergo delayed development on yeast diet. We propose that microbial cell size or bite size could be one of the crucial factors in regulation of feeding in C. elegans.\n\nIMPORTANCEThe microbiome in C. elegans gut is composed of diverse genera of bacteria but it lacks yeast and other fungi. In this study, we provide evidence that yeast cell size is bigger than the mouth size of C. elegans larvae. We propose that \"bigger than the bite size of yeast cells is one possible reason for low satiety on yeast diet, reduced feeding, lower stored lipids and delayed development. The bite size threshold imposed by C. elegans mouth can, partly, explain absence of yeast in C. elegans native gut microbiome and \"bite size can be studied further as a determinant of microbiome diversity in other animals.