Analyzing Egg Laying Behaviors in C. elegans Based on Bacterial Food Sources

Abstract

Caenorhabditis elegans is a non-parasitic nematode that feeds on soil bacteria. It has been shown that these organisms prefer to consume strains of E. coli bacteria, which are Gram negative, over strains of Bacillus bacteria, which are Gram positive. It was hypothesized that the food preference of the nematodes relates to the survival of the fittest concept, so that worms who consume Gram negative bacteria have greater reproductive success than worms who consume Gram positive bacteria. To test this hypothesis, the nematodes were fed two types of Gram negative bacteria and one type of Gram positive bacteria, and reproductive success was measured as the number of eggs the worms could lay after a specific time period. The results showed that the number of eggs laid by the worms fed Gram positive bacteria was significantly less than the number of eggs laid by worms fed Gram negative bacteria. In addition, a gene expression study using real-time PCR to amplify two egg-laying genes and two dauer-formation genes was conducted. Three of the four genes investigated are part of the TGFβ superfamily of genes that are known to be involved in many stages of reproduction and embryogenesis. The results showed that worms fed Gram negative bacteria had a higher expression of the genes tested than the worms fed Gram positive bacteria, concluding that reproductive abilities of nematodes can be affected by a food source. The mechanism by which bacterial food source affects reproduction needs further investigation, but these data indicate there may be a link between the immune system, diet, and reproduction.