Cross-Feeding of Escherichia coli Mutants Defective in the Biosynthesis of Nicotinamide Adenine Dinucleotide

Mutants ofEscherichia coli defective in the biosynthesis of nicotinamide adenine dinucleotide (NAD) are able to grow in a Casamino Acids medium lacking NAD and its immediate precursors, nicotinic acid and nicotinamide. This property has allowed the development of a system to measure cross-feeding between anadA and anadB mutant. This system provides a means of isolating the intermediate, prequinolinic acid, as well as a biological assay for the compound. ThenadB mutant feeds thenadA mutant, indicating that thenadA enzyme occurs first in the pathway and thenadB enzyme second. No cross-feeding was detected betweennadA andnadC or betweennadB andnadC .