Quinolone antibiotics enhance denitrifying anaerobic methane oxidation in Wetland sediments: Counterintuitive results

Denitrifying anaerobic methane oxidation (DAMO) plays an important role in the element cycle of wetlands. In recent years, the content of antibiotics in wetlands has gradually increased due to human activities. However, the impact of antibiotics on the ecological function of DAMO remains unclear. Here we studied the influence of three high-content quinolone antibiotics (QNs) on DAMO in the sediments of the Baiyangdian Wetland. The results show that QNs can significantly promote the potential DAMO rates. Moreover, the enhancement of potential DAMO rates is positively correlated with the dosage of QNs. This promotion effect of QNs on nitrate-DAMO can be attributed to the hormesis phenomenon or their inhibition of substrate competitors. As antibacterial agents, QNs inhibit nitrite-DAMO conducted by bacteria, but greatly promote nitrate-DAMO conducted by archaea. These results suggest that the short-term effect of QNs on DAMO in wetlands is promotion rather than inhibition.

Coupled methane and nitrous oxide biotransformation in freshwater wetland sediment microcosms

Anaerobic oxidation of methane (AOM) coupled to denitrification is becoming the focus of scientific inquiry due to its potential contribution to global carbon and nitrogen cycles. AOM has been previously reported to proceed with nitrate (NO₃^-) or nitrite (NO₂^-). However, little research has been conducted on the simultaneous use of methane (CH₄) and nitrous oxide (N₂O). Here, coupled CH₄ and N₂O biotransformation in a freshwater wetland sediment was obtained in a 7-day anaerobic sediment incubation assay. The significant CO₂ accumulation and decrease of CH₄ emission in sediment microcosms was attributed to two mechanisms: inhibition of methanogenesis and N₂O-dependent AOM. To further confirm the coupled CH₄ and N₂O transformation, a ¹³C-labelled stable isotope tracer assay after anaerobic incubation was conducted with N₂O and/or CH₄ amendments. The N₂O-dependent AOM rate was 3.41 ± 0.13 nmol CO₂ g^-1 dry sediment·day^-1. According to metagenomic analysis, addition of N₂O stimulated AOM by increasing the activity and abundance of methanotrophic bacteria and by increasing enzymatic activities in the electron transport chain. Based on these results, we propose coupled CH₄ and N₂O biotransformation in the sediment microcosms for the first time, carried out by unidentified methanotroph(s) via intra‑oxygen produced in the presence of N₂O. Such a process has the potential to reduce the emission of two highly potent greenhouse gases and makes a significant contribution to the link of global carbon and nitrogen cycles in anoxic environments.