Identification of an assimilatory nitrate reductase in mutants of Paracoccus denitrificans GB17 deficient in nitrate respiration

Abstract

A Paracoccus denitrificans strain (M6Omega) unable to use nitrate as a terminal electron acceptor was constructed by insertional inactivation of the periplasmic and membrane-bound nitrate reductases. The mutant strain was able to grow aerobically with nitrate as the sole nitrogen source. It also grew anaerobically with nitrate as sole nitrogen source when nitrous oxide was provided as a respiratory electron acceptor. These growth characteristics are attributed to the presence of a third, assimilatory nitrate reductase. Nitrate reductase activity was detectable in intact cells and soluble fractions using nonphysiological electron donors. The enzyme activity was not detectable when ammonium was included in the growth medium. The results provide an unequivocal demonstration that P. denitrificans can express an assimilatory nitrate reductase in addition to the well-characterised periplasmic and membrane-bound nitrate reductases.

Properties of the periplasmic nitrate reductases fromParacoccus pantotrophusandEscherichia coliafter growth in tungsten-supplemented media

“…3 ) is an important component of the biological nitrogen cycle. It serves as the substrate for deni-tri¢cation, whereby nitrate is reduced via nitrite (NO 3 2 ), nitric oxide (NO) and nitrous oxide (N 2 O) to dinitrogen (N 2 ), but can also be reduced via nitrite to ammonium as part of nitrogen assimilation and respiration [1]. Many bacteria can express multiple, biochemically distinct, nitrate reductases.…”

Physiological and evolutionary studies of NAP systems in Shewanella piezotolerans WP3

“…The first NAR serves at high nitrate concentration (Potter et al, 1999), the second NAR is expressed in response to stress and is part of the RpoS regulon (Spector et al, 1999); and the NAP enzyme is primarily expressed at low nitrate concentrations, and assists the nitrate respiration via NAR, in which bioenergetic efficiency is limited (Stewart et al, 2002). Paracoccus pantaotrophus contains NAS, NAR and NAP, and each of them serves different functions (Sears et al, 1997, Tabata et al, 2005.…”

Expression ofBradyrhizobium japonicum cbb3 terminal oxidase under denitrifying conditions is subjected to redox control

“…Regulation of gene expression mediated by the oxidation state of the carbon substrate has been reported in Paracoccus pantotrophus (Richardson & Ferguson, 1992; Sears et al , 2000; Ellington et al , 2002, 2006) and P. denitrificans (Sears et al , 1997). In both species, expression of the nap operon, encoding the periplasmic nitrate reductase, is maximal when cells are grown aerobically with a reduced carbon source such as butyrate.…”