ABSTRACT
By using mini-Tn5 transposon mutagenesis, random transcriptional fusions of promoterless bacterial luciferase,luxAB, to genes of Pseudomonas putida KT2442 were generated. Insertion mutants that responded to ammonium deficiency by induction of bioluminescence were selected. The mutant that responded most strongly was genetically analyzed and is demonstrated to bear the transposon within the assimilatory nitrate reductase gene (nasB) of P. putida KT2442. Genetic evidence as well as sequence analyses of the DNA regions flanking nasBsuggest that the genes required for nitrate assimilation are not clustered. We isolated three second-site mutants in which induction ofnasB expression was completely abolished under nitrogen-limiting conditions. Nucleotide sequence analysis of the chromosomal junctions revealed that in all three mutants the secondary transposon had inserted at different sites in the gltB gene of P. putida KT2442 encoding the major subunit of the glutamate synthase. A detailed physiological characterization of thegltB mutants revealed that they are unable to utilize a number of potential nitrogen sources, are defective in the ability to express nitrogen starvation proteins, display an aberrant cell morphology under nitrogen-limiting conditions, and are impaired in the capacity to survive prolonged nitrogen starvation periods.
NiaA, the structural nitrate reductase gene of Phytophthora infestans: isolation, characterization and expression analysis in Aspergillus nidulans
