UC Davis

Giardia lamblia is a protozoan intestinal pathogen that infects a wide range of mammals, including humans. The global burden of giardiasis is especially detrimental to young children in developing countries. Evidence of drug-tolerant and drug-resistant strains have been reported. Giardia has a unique microaerophilic metabolism, with many potential druggable targets, but further research is needed. To study the effect of specific metabolites, I first designed a defined base medium and then added known concentrations of metabolites to that base medium. ATP generation was measured using a luminescence assay and the transcriptomic response to specific metabolites was measured using RNA-Seq analysis. Amino acids, not glucose, were found to have a significant effect on ATP generation and transcriptional response to nutrient availability. The arginine dihydrolase (ADH) pathway plays an important role in Giardia amino acid metabolism, generating one molecule of ATP from one molecule of arginine. The potential energy flux through the ADH pathway is approximately 7-8 fold higher than that from glucose and the energy produced through the ADH pathway is also thought to compensate for the reduction of ATP generation from glycolysis that occurs during encystation. Using CRIPSR-Cas9 technology, the first complete metabolic knockout in Giardia was created, disrupting all four copies of the arginine deiminase (ADI) gene. When ADI is knocked out, there was a significant reduction in ATP generation through the ADH pathway and down regulation of genes associated with amino acid metabolism.