Watsuji Tomo-o, Takaya Naoki, Nakamura Akira, Shoun Hirofumi
Institute of Applied Biochemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
Biosci Biotechnol Biochem. 2003 May;67(5):1115-20. doi: 10.1271/bbb.67.1115.
The denitrifying fungus Cylindrocarpon tonkinense was thought to be able to denitrify only nitrite (NO2-) but not nitrate (NO3-) to form nitrous oxide (N2O). Here we found, however, that C. tonkinense can denitrify NO3- under certain conditions. Presence of ammonium (NH3+) in addition to NO3- and the use of a fermentable sugar as an electron donor were key conditions for inducing the denitrifying activity. Such induction accompanied a remarkable increase in the intracellular level of the enzyme activities related to NO3- metabolism. These activities contained assimilatory type NADPH (or NADH)-dependent NO3- reductase (aNar), dissimilatory nitrite reductase (dNir), and nitric oxide reductase (P450nor), but did not contain ubiquinol-dependent, dissimilatory NO3- reductase (dNar). The denitrification was inhibited by tungstate, an inhibitor of Nar. These results demonstrated occurrence of a novel type of denitrification in C. tonkinense, in which assimilatory type Nar is possibly involved.
反硝化真菌东京柱孢菌曾被认为仅能将亚硝酸盐（NO₂⁻）而非硝酸盐（NO₃⁻）反硝化生成一氧化二氮（N₂O）。然而，我们在此发现，东京柱孢菌在特定条件下能够将NO₃⁻反硝化。除了NO₃⁻之外铵（NH₃⁺）的存在以及使用可发酵糖作为电子供体是诱导反硝化活性的关键条件。这种诱导伴随着与NO₃⁻代谢相关的酶活性在细胞内水平的显著增加。这些活性包括同化型NADPH（或NADH）依赖的NO₃⁻还原酶（aNar）、异化亚硝酸盐还原酶（dNir）和一氧化氮还原酶（P450nor），但不包括泛醇依赖的异化NO₃⁻还原酶（dNar）。反硝化作用受到Nar抑制剂钨酸盐的抑制。这些结果证明了东京柱孢菌中存在一种新型反硝化作用，其中同化型Nar可能参与其中。
