Use of chlorate as a selective inhibitor to distinguish membrane-bound nitrate reductase (Nar) and periplasmic nitrate reductase (Nap) of dissimilative nitrate reducing bacteria in sediment

The use of chlorate as a selective inhibitor of dissimilative nitrate reduction was studied using pure cultures of Comamonas testosteroni (a denitrifier) and Klebsiella pneumoniae (a nitrate-ammonifier) isolated from estuarine sediment, and in sediment slurry. Pure culture experiments demonstrated that chlorate selectively inhibited membrane-bound nitrate reductase (Nar) activity, probably by blocking nitrate transporters (NarK). Sediment slurry experiments showed that chlorate inhibited nitrate reduction and N(2)O formation, but did not inhibit nitrite reduction and its N(2)O formation, indicating that chlorate selectively inhibited only the first step of nitrate reduction. Chlorite chemically oxidized nitrite to nitrate and could not be used as a selective inhibitor of nitrite metabolism, although chlorite apparently selectively inhibited formation of N(2)O from nitrite. Chlorate can be used as a specific inhibitor to distinguish between nitrate reduction by Nap or Nar in natural communities of microorganisms.