E. coli folate synthesis and C. elegans ageing: Investigating the effect of sulfamethoxazole on bacterial lawn morphology and metabolism

Abstract

The gut microbiota is essential for host nutrition and may influence ageing. The nematode worm C. elegans provides a useful simplified model for investigating bacterial-host interactions. E. coli is used as a food source for C. elegans. Previous research has shown a decrease in E. coli folate synthesis results in extension of C. elegans lifespan. Potential detrimental effects of bacteria when producing normal amounts of folate are unlikely to be mediated by bacterial growth rate or direct effects of folate on the nematode. Potential toxicity of metabolic chemicals produced by wild type E. coli could explain the shorter lifespan of C. elegans. This thesis aims to understand the interaction between E. coli and C. elegans by investigating components that may be affected by folate synthesis and influencing lifespan.

Toxicity from bacterial formaldehyde synthesis was explored with a formaldehyde sensing lacZ reporter. A novel method was developed to quantify reporter output in a bacterial lawn. The lifespan of C. elegans maintained on E. coli constitutively expressing the formaldehyde detoxification enzymes FrmA/B was also investigated. Formaldehyde synthesis was not found to be a source of toxicity that accelerates C. elegans ageing. The effect of sulfamethoxazole on bacterial lawn growth, morphology and proliferation was examined and found to alter morphology, attenuate growth and impair proliferation compared to wild type and lifespan increasing mutant E. coli. A novel LC-MS/MS method was developed to analyse amino acids in agar. It revealed sulfamethoxazole alters bacterial amino acid metabolism associated with the serine-glycine pathway and growth. The absence of glycine in the media was also examined. It revealed changes to the exometabolome in both sulfamethoxazole treated and untreated conditions that may slow C. elegans ageing without altering bacterial growth.
This work developed novel methods for exploring the bacterial lawn and metabolism, providing insight into the mechanism of how sulfamethoxazole disruption of bacterial folate synthesis may influence C. elegans ageing.