Genetics of Denitrification in Pseudomonas Aeruginosa and Stutzeri

Abstract

Genetic studies on denitrifiers have been largely limited to Pseudomonas aeruginosa because of its well studied genetic systems of gene transfer—conjugative and transductional. Studies on this organism have identified and located a number of genes encoding the enzymes that mediate nitrate reduction including the assimilatory and dissimilatory nitrate and nitrite reductases. All of these are chromosomically located and none is contiguous with another. These studies also revealed the biochemical explanation for assimilatory and dissimilatory nitrate reduction being catalyzed by distinct enzyme: the dissimilatory enzyme cannot function in the presence of oxygen because electrons from the membrane-associated transport chain flow preferentially to it rather than nitrate.

In spite of its many advantages as an paradigm for physiological genetic studies on denitrification, its uniqueness among denitrifiers investigated so far in not being able to grow with N₂O as sole oxidant severely limit its utility for investigations on the later steps of the denitrification pathway. Pseudomonas stutzeri grows well on exogenous N₂O as sole oxidant, but its use in physiological genetic studies required the development of procedures for genetic exchange and manipulation. Procedures for genetic exchange by transformation, insertion mutagenesis, and mapping have been developed recently making this organism an excellent subject for future studies.