Studies on hypersaline-tolerant white-rot fungi IV: effects of Mn²⁺ and NH₄ ⁺ on manganese peroxidase production and Poly R-478 decolorization by the marine isolate Phlebia sp. MG-60 under saline conditions

Abstract

Manganese peroxidase (MnP) production by Phlebia sp. MG-60 is strongly regulated by Mn²⁺ and NH₄ ⁺ at various sea salt incubation conditions. Extra-added Mn²⁺ and NH₄ ⁺ obviously inhibited MnP production, but sea salts relieved the inhibition partially or completely. Three media were prepared: Kirk medium with addition of 0%–5% sea salts (KS medium), a high level of Mn²⁺ (300 mg/l) in KS medium (HM-KS medium), and a high level of NH₄ ⁺ (430 mg/l) in KS medium (HN-KS medium). Without addition of sea salts, the dye Poly R-478 was significantly decolorized by low MnP activity (about 200 U/l) and a low level of laccase activity (about 100 U/l) in KS and HM-KS media. In the cultures in which laccase activity was almost completely inhibited by 3% and 5% sea salts, MnP activity higher than 400 U/l was necessary for Poly R-478 decolorization in all of the three media. We first report the linear correlation of MnP activity and decolorization of Poly R-478 under saline conditions and the effect of laccase on this relation.