GENETIC-LINKAGE IN PSEUDOMONAS-AERUGINOSA OF ALGT AND NADB - MUTATIONIN NADB DOES NOT AFFECT NAD BIOSYNTHESIS OR ALGINATE PRODUCTION

The 68-min region of the chromosome of Pseudomonas aeruginosa (Pa) con tains the gene algT, encoding a putative alternate sigma factor simila r to sigma(E) in Escherichia coli, that is required for the expression of several genes in the alginate biosynthetic regulon. Sequences imme diately upstream from algT were found to contain a divergently express ed open reading frame encoding a 60-kDa protein with 64 and 36% identi ty to the nadB gene products of E. coli and Bacillus subtilis, respect ively. The nadB gene encodes L-aspartate oxidase and has been shown in several bacteria to be essential for de novo nicotinamide-adenine din ucleotide (NAD) biosynthesis. Pa nadB complemented the growth requirem ent for nicotinic acid in a nadB mutant strain of E. coli, suggesting that this gene encodes a functional homologue of L-aspartate oxidase. A nadB::Tn501 mutant was constructed by gene replacement in the algina te-producing strain, Pa FRD. This NadB(-) mutant still produced algina te and appeared normal with respect to the regulation of alginate synt hesis. Interestingly, the NadB(-) mutant did not have an auxotrophic p henotype for nicotinic acid, indicating that this nadB was not essenti al for NAD biosynthesis in Pa. These results suggest the possibility t hat Pa has an alternate mechanism for de novo NAD biosynthesis.