The negative impacts on the ecosystem of antibiotic residues in the environment have become a global concern. However, little is known about the transformation mechanism of antibiotics by manganese peroxidase (MnP) from microorganisms. This work investigated the transformation characteristics, the antibacterial activity of byproducts, and the degradation mechanism of tetracycline (TC) by purified MnP from Phanerochaete chrysosporium. The results show that nitrogen-limited and high level of Mn²⁺ medium could obtain favorable MnP activity and inhibit the expression of lignin peroxidase by Phanerochaete chrysosporium. The purified MnP could transform 80% tetracycline in 3 h, and the threshold of reaction activator (H₂O₂) was about 0.045 mmol L⁻¹. After the 3rd cyclic run, the transformation rate was almost identical at the low initial concentration of TC (77.05–88.47%), while it decreased when the initial concentration was higher (49.36–60.00%). The antimicrobial potency of the TC transformation products by MnP decreased throughout reaction time. We identified seven possible degradation products and then proposed a potential TC transformation pathway, which included demethylation, oxidation of the dimethyl amino, decarbonylation, hydroxylation, and oxidative dehydrogenation. These findings provide a novel comprehension of the role of MnP on the fate of antibiotics in nature and may develop a potential technology for tetracycline removal.

Bacterial diversity and its distribution characteristics in sediments are critical to understanding and revealing biogeochemical cycles in sediments. However, little is known about the relationship between biogeochemistry processes and vertical spatial distribution of bacterial communities in sandy sediments. In this study, we used fluorescence quantitative PCR, high-throughput sequencing technology and statistical analysis to explore the vertical distribution pattern of bacterial community diversity and its influencing factors in sandy sediments of the Yangtze River Basin. The aim is to enrich the understanding of the ecological characteristics and functions of bacteria in river ecosystems. The results showed that both sediment bacterial abundance and diversity showed a gradual decrease from surface to bottom in the vertical distribution. The main environmental factors that influenced the bacterial distribution pattern were pore water dissolved oxygen (DO), total nitrogen (TN) concentration and sediment nitrogen (N) content. The dominant bacterial species, Massilia and Flavobacterium, are suitable for growth and reproduction in high oxygen and nutrient-richer environments, while Limnobacter prefers low oxygen or anaerobic conditions. The vertical distribution pattern of bacteria and its influencing factors in river sandy sediment found in this study differ from the results in mud sediment, which may be related to the larger granular gap between sandy sediment and the lower content of organic matter. The findings of this study further our understanding of the distribution patterns and ecological preferences of microbial communities in river sediments, providing insights into how these communities may adapt to varying environmental conditions.

The ecological risks brought by sulfadiazine (SDZ) residues in the environment have put forward requirements for efficient antibiotic treatment technologies. In this study, biogenic manganese oxides (BMOs) were synthesized using the bacterium Stenotrophomonas maltophilia DT1, and a BMO/syringaldehyde (SYR) system was constructed for SDZ degradation to investigate its performance, mechanism, and potential application. Results showed that the DT1-synthesized BMO contained Mn (II/III/IV) and defect-related oxygen species, which enabled the BMO to participate in SYR activation and SDZ transformation. A total of 99.67% of 10 mg/L SDZ was removed within 3 h under optimized conditions. Humic acid and most environmental ions had no significant interference with the system, except for slight inhibition by Fe³⁺ and Mn²⁺. Three degradation pathways of SDZ were elucidated through the identification of five transformation products and density functional theory calculations. ECOSAR toxicity prediction and growth inhibition of Escherichia coli revealed that the degradation products exhibited significantly reduced toxicity. Furthermore, the BMO exhibited 4.41–17.47 times higher SYR-mediated SDZ transformation efficiency than chemically synthesized manganese oxide (CMO) and showed good performance in reuse tests and real water matrices. This study provides an efficient and eco-friendly green technology for the remediation of SDZ pollution in aquatic environments and provides potential support for the removal of refractory pollutants mediated by BMO.