Molecular Biology of Respiratory Nitrate Reduction (Denitrification) of Pseudomonas Stutzeri

Abstract

Respiratory nitrate reduction by bacteria (denitrification) consists in the sequential transformation of an ionic N-oxide to dinitrogen. The process is catalyzed by four different metalloenzymes which, for the first time, were all purified to homogeneity from the same denitrifying bacterium, Pseudomonas stutzeri ZoBell (ATCC 14405). Full understanding of a biological system such as denitrification requires knowledge of the structure and function of the genes and their arrangement within the genome. Denitrification is plasmid-coded in the lithoautotrophic bacterium Alcaligenes eutrophus HI6 (Schneider et al. 1988). The genus Pseudomonas harbors many species that were shown to carry plasmids with important metabolic functions, but it is not known whether denitrification would also be plasmid-coded. To detect plasmids in P. stutzeri standard procedures and those specifically designed to preserve megaplasmids were applied (Eckhardt 1978; Simon 1984; Nies et al. 1987). The plasmid preparations were subjected to pulsed field gel electrophoresis (CHEF variant), a technique which would facilitate the identification of megaplasmids because of an increased band-sharpening of DNA-molecules with several megabase pairs in size. No indications for plasmids were found, so we consider denitrification of P. stutzeri to be chromosomally encoded.