Codenitrification and Denitrification Are Dual Metabolic Pathways through Which Dinitrogen Evolves from Nitrate in Streptomyces antibioticus

Abstract

ABSTRACT We screened actinomycete strains for dinitrogen (N 2 )-producing activity and discovered that Streptomyces antibioticus B-546 evolves N 2 and some nitrous oxide (N 2 O) from nitrate (NO 3 − ). Most of the N 2 that evolved from the heavy isotope ([ 15 N]NO 3 − ) was 15 N 14 N, indicating that this nitrogen species consists of two atoms, one arising from NO 3 − and the other from different sources. This phenomenon is similar to codenitrification in fungi. The strain also evolved less, but significant, amounts of 15 N 15 N from [ 15 N]NO 3 − in addition to 15 N 15 NO with concomitant cell growth. Prior to the production of N 2 and N 2 O, NO 3 − was rapidly reduced to nitrite (NO 2 − ) accompanied by distinct cell growth, showing that the actinomycete strain is a facultative anaerobe that depends on denitrification and nitrate respiration for anoxic growth. The cell-free activities of denitrifying enzymes could be reconstituted, supporting the notion that the 15 N 15 N and 15 N 15 NO species are produced by denitrification from NO 3 − via NO 2 − . We therefore demonstrated a unique system in an actinomycete that produces gaseous nitrogen (N 2 and N 2 O) through both denitrification and codenitrification. The predominance of codenitrification over denitrification along with oxygen tolerance is the key feature of nitrate metabolism in this actinomycete.