Denitrification by the fungus Cylindrocarpon tonkinense: anaerobic cell growth and two isozyme forms of cytochrome P-450nor

Abstract

We examined the denitrification system of the fungus Cylindrocarpon tonkinense and found several properties distinct from those of the denitrification system of Fusarium oxysporum. C. tonkinense could form N 2 O from nitrite under restricted aeration but could not reduce nitrate by dissimilatory metabolism. Nitrite-dependent N 2 O formation was accompanied by distinct cell growth. N 2 O formation and/or cell growth during the anaerobic culture was not affected by further addition of ammonium ions but was suppressed by respiration inhibitors such as rotenone or antimycin, suggesting that denitrification plays a physiological role in respiration. Dissimilatory nitrite reductase and nitric oxide reductase (Nor) activities could be detected in cell extracts of the denitrifying cells. The Nor activity was purified and found to depend on two isozymes of cytochrome P-450nor (P-450nor), which were designated P-450nor1 and P-450nor2. These isozymes differed in the N-terminal amino acid sequence, isoelectric point, specificity to the reduced pyridine nucleotide (NADH or NADPH), and the reactivity to the antibody to P-450nor of F. oxysporum. The difference between the specificities to NADH and NADPH suggests that P-450nor1 and P-450nor2 play different roles in anaerobic energy acquisition.

Purification and cDNA cloning of nitric oxide reductase cytochrome P450nor (CYP55A4) from Trichosporon cutaneum

“…The specific activity of the purified Nor determined under the conditions described was 12 700 nmol NO per min per nmol P450 using NADH as an electron donor, which was similar to the value with F. oxysporum P450nor [7]. The purified P450 also exhibited a high NADPH-dependent Nor activity (10 540 nmol NO per min per nmol P450), indicating that its specificity for the electron donors, NADH and NADPH, is low like P450nor2 from C. tonkinense [4].…”

“…The antibodies against P450nor of F. oxysporum do not necessarily react with P450nors of other fungi. For example, they react with P450nor1 of C. tonkinense [4] but do not react with its isozyme (P450nor2) (unpublished data). Therefore, the results of Western blotting (Fig.…”

Denitrification by yeasts and occurrence of cytochrome P450nor in Trichosporon cutaneum

“…oxysporum, Fus. lini, Cylindrocarpon tonkinense, and Gibberella fujikuroi [5,6,8,13] that belong to teleomorphic and anamorphic genera of ascomycetes closely related to each other. So the present ¢nding is very important in that it extends the range of distribution of P450nor among fungi.…”

“…The cell-free extracts of both T. cutaneum JCM 2390 and T. cutaneum JCM 2391 contained a protein that reacted with the antibodies against P450nor of Fus. oxysporum [6], whereas those of F. fuzhouensis or Candida sp. did not.…”

Nitrous oxide production by the ectomycorrhizal fungi Paxillus involutus and Tylospora fibrillosa

“…Soils are the major source of the greenhouse gas nitrous oxide (N 2 O) (Solomon et al, 2007), and there are several soil-inhabiting microbial groups capable of producing N 2 O (Baggs, 2008;Hayatsu et al, 2008). Direct evidence for the potential role of filamentous fungi in this production has been gained from pure culture studies of the model fungal denitrifiers Fusarium oxysporum and Fusarium lichenicola Tanimoto et al, 1992;Usuda et al, 1995;Kobayashi et al, 1996;Zhou et al, 2001). These fungal denitrifiers are prevalent in agricultural soils with a neutral pH (Fritze & Bååth, 1993).…”