A novel enrofloxacin-degrading fungus, Humicola sp. KC0924g, isolated from the rhizosphere sediment of the submerged macrophyte Vallisneria spiralis L.

A novel enrofloxacin-degrading fungus was isolated from a rhizosphere sediment of the submerged macrophyte Vallisneria spiralis L.. The isolate, designated KC0924g, was identified as a member of the genus Humicola based on morphological characteristics and tandem conserved sequence analysis. The optimal temperature and pH for enrofloxacin degradation by strain KC0924g were 28 °C and 9.0, respectively. Under such condition, 98.2% of enrofloxacin with an initial concentration of 1 mg L^-1 was degraded after 72 h of incubation, with nine possible degradation products identified. Four different metabolic pathways were proposed, which were initiated by cleavage of the piperazine moiety, hydroxylation of the aromatic ring, oxidative decarboxylation, or defluorination. In addition to enrofloxacin, strain KC0924g also degraded other fluoroquinolone antibiotics (ciprofloxacin, norfloxacin, and ofloxacin), malachite green (an illegal additive in aquaculture), and leucomalachite green. Pretreatment of cells of strain KC0924g with Cu²⁺ accelerated ENR degradation. Furthermore, it was speculated that a flavin-dependent monooxygenase was involved in ENR degradation, based on the increased transcriptional levels of these two genes after Cu²⁺ induction. This work enriches strain resources for enrofloxacin remediation and, more importantly, would facilitate studies on the molecular mechanism of ENR degradation with degradation-related transcriptome available.