The Possible Involvement of Copper-Containing Nitrite Reductase (NirK) and Flavohemoglobin in Denitrification by the Fungus Cylindrocarpon tonkinense

The occurrence of denitrification and nitrate respiration among eukaryotes has been established during the last few decades. However, denitrification-related eukaryotic genes have been isolated from only a few fungi, and eukaryotic denitrification (or nitrate respiration) is still inadequately understood. In this study, we identified genes that were up-regulated under denitrifying conditions in the fungus Cylindrocarpon tonkinense using the suppression subtraction hybridization technique, and the expression patterns of these genes were characterized by Northern analysis. We identified copper-containing nitrite reductase, cytochrome P450 nitric oxide reductase, flavohemoglobin (Fhb), and formate/nitrite transporter homolog genes as possibly involved in fungal denitrification. Our results concerning the involvement of Fhb and formate/nitrite transporter perhaps provide new insight into the fungal denitrification system.