Anaerobic biodegradation of four sulfanilamide antibiotics: Kinetics, pathways and microbiological studies

Synthesis of Cu Nanoparticles Incorporated Mesoporous C/SiO2 for Efficient Tetracycline Degradation

In this study, a Cu NPs-incorporated carbon-containing mesoporous SiO2 (Cu/C-SiO2) was successfully synthesized through a grinding-assisted self-infiltration method followed by an in situ reduction process. The obtained Cu/C-SiO2 was then employed as a Fenton-like catalyst to remove tetracycline (TC) from aqueous solutions. TEM, EDS, XRD, N2 adsorption-desorption, FTIR, and XPS methods were used to characterize the crystal structure, morphology, porosity, chemical composition, and surface chemical properties of the catalyst. The effects of initial TC concentration, catalyst dosage, H2O2 dosage, solution pH, HA addition, and water media on the TC degradation over Cu/C-SiO2 were investigated. Scavenging and electrochemical experiments were then carried out to analyze the TC degradation mechanism. The results show that the Cu/C-SiO2 can remove 99.9% of the concentrated TC solution (C0 = 500 mg·L-1), and it can be used in a wide pH range (R.E. = 94-99%, pH = 3.0-11.0). Moreover, hydroxyl radicals (•OH) were detected to be the dominant reactive species in this catalytic system. This study provides a simple and promising method for the synthesis of heteroatom-containing mesoporous catalysts for the decomposition of antibiotics in wastewater.

Metagenomic analysis revealed sources, transmission, and health risk of antibiotic resistance genes in confluence of Fenhe, Weihe, and Yellow Rivers

Rivers are important vectors and reservoirs of antibiotics resistance genes (ARGs). Information regarding transmission and health risk of ARGs in river confluence is still lacking. In this study, metagenomics was used to distinguish contributions of human activities on ARGs and human pathogenic bacteria (HPB) in confluence of Fenhe, Weihe, and Yellow Rivers. Bacitracin resistance gene and bacA were the highest in all rivers, with 1.86 × 10^-2-7.26 × 10^-2 and 1.79 × 10^-2-9.12 × 10^-2 copies/16S rRNA copies, respectively. River confluence significantly increased the abundance of ARGs, especially at the confluence of three rivers with the highest 1.53 × 10^-1 copies/16S rRNA copies. Antibiotic efflux and antibiotic target alteration were the dominant resistant mechanisms in three rivers. ARGs profiles were influenced by multiple factors, with the contributions of various factors ranked as microbial communities > physicochemical factors > human activities > mobile genetic elements (MGEs). Notably, human activities and animal feces were important potential contributors of ARGs in the Weihe River and Yellow River. Transposons, as the main MGEs in three rivers, played important roles in ARGs transfer. The confluence of three rivers had the highest abundance of MGEs with the greatest transfer potentials, and therefore exhibiting the largest exposure risk of ARGs with 232.4 copies/cap·d. Furthermore, correlations of ARGs, MGEs, and HPB in different rivers were constructed via co-occurrence modes to systematically illustrate the health risks of ARGs. This study firstly unveiled the transmission and health risk of ARGs in river confluence, providing supports for ARGs control in watershed.

Analysis of the Comparative Growth Kinetics of Paenarthrobacter ureafaciens YL1 in the Biodegradation of Sulfonamide Antibiotics Based on Substituent Structures and Substrate Toxicity

The high consumption and emission of sulfonamide antibiotics (SAs) have a considerable threat to humans and ecosystems, so there is a need to develop safer and more effective methods than conventional strategies for the optimal removal of these compounds. In this study, four SAs with different substituents, sulfadiazine (SDZ), sulfamerazine (SMR), sulfamethoxazole (SMX), and sulfamethazine (SMZ) were removed by a pure culture of Paenarthrobacter ureafaciens YL1. The effect of the initial SAs concentration on the growth rate of strain YL1 was investigated. The results showed that the strain YL1 effectively removed various SAs in the concentration range of 0.05–2.4 mmol·L−1. The Haldane model was used to perform simulations of the experimental data, and the regression coefficient of the model indicated that the model had a good predictive ability. During SAs degradation, the maximum specific growth rate of strain YL1 was ranked as SMX > SDZ > SMR > SMZ with constants of 0.311, 0.304, 0.302, and 0.285 h−1, respectively. In addition, the biodegradation of sulfamethoxazole (SMX) with a five-membered substituent was the fastest, while the six-membered substituent of SMZ was the slowest based on the parameters of the kinetic equation. Also, density functional theory (DFT) calculations such as frontier molecular orbitals (FMOs), and molecular electrostatic potential map analysis were performed. It was evidenced that different substituents in SAs can affect the molecular orbital distribution and their stability, which led to the differences in the growth rate of strain YL1 and the degradation rate of SAs. Furthermore, the toxicity of P. ureafaciens is one of the crucial factors affecting the biodegradation rate: the more toxic the substrate and the degradation product are, the slower the microorganism grows. This study provides a theoretical basis for effective bioremediation using microorganisms in SAs-contaminated environments.

Dissipation rates, residue distribution, degradation products, and degradation pathway of sulfoxaflor in broccoli

Broccoli was selected as the research object in this paper to reveal the dissipation, distribution, and degradation pathway of sulfoxaflor under greenhouse and open-field cultivation conditions for the ecological risk assessment of sulfoxaflor. Results showed that the dissipation of sulfoxaflor in broccoli leaves, flowers, stems, roots, and the whole broccoli was in accordance with the first-order kinetic equation. The sulfoxaflor concentration in broccoli roots reached the maximum value after 1 day of application and then gradually decreased. The degradation half-lives of sulfoxaflor in the roots, leaves, flowers, stems, and whole broccoli were between 2.3 and 19.8 days. The longest degradation half-life of sulfoxaflor was in Heilongjiang under greenhouse cultivation. The terminal residue of sulfoxaflor in broccoli was in the range of 0.005-0.029 mg/kg, and the proportion of sulfoxaflor residue in broccoli leaves was the largest. Thirteen transformation products were separated and identified by ultrahigh-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, and their kinetic evolution was studied. The cleavage of the N = S bond, C-S bond, C-O bond, and cyanide, as well as glucosylation, hydroxylation, SO extrusion, elimination, sulfhydrylation, ketonization, defluorination, and rearrangement, was inferred as the mechanism. Overall, these results can provide guidance for the supervision of the safe application of sulfoxaflor.

Anaerobic sulfamethoxazole-degrading bacterial consortia in antibiotic-contaminated wetland sediments identified by DNA-stable isotope probing and metagenomics analysis

Anaerobic degradation has been demonstrated as an important pathway for the removal of sulfonamide (SA) in contaminated environments, and identifying the microorganisms responsible for the degradation of SA is a key step in developing bioaugmentation approaches. In this study, we investigated the anaerobic degradation activity of three SA [sulfadiazine (SDZ), sulfamethazine (SMZ) and sulfamethoxazole (SMX)] and the associated bacterial community in wetland sediments contaminated by aquaculture (in Fujian Province, coded with FJ), livestock farming (in Sichuan Province, coded with SC), or rural wastewaters (in Guangdong Province, coded with GD). Additionally, the combination of DNA-stable isotope probing (SIP) with metagenomics was further applied to assess the active SA-degrading microbes using SMX as a model SA. Among SDZ, SMZ and SMX, only SMX could be effectively dissipated, and the degradation of SMX was relatively fast in the microcosms of sediments with higher levels of SA contamination (FJ and SC). The anaerobic biotransformation pathway of SMX was initiated by hydrogenation with the cleavage of the N-O bond on the isoxazole ring. DNA-SIP revealed that the in situ active anaerobic SMX-degraders (5, 18 and 3 genera in sediments FJ, SC and GD respectively) were dominated by Proteobacteria in sediments FJ and SC, but by Firmicutes (two Family XVIII members) in sediment GD. Mycobacterium, unclassified Burkholderiaceae and Rhodocyclaceae were identified as the dominant active SMX-degrading bacteria in both sediments FJ and SC. Higher proportions of antibiotic resistance gene and genes involved in various functional categories were observed in sediments FJ and SC.

Tailoring a novel hierarchical cheese-like porous biochar from algae residue to boost sulfathiazole removal

Aquatic pollution caused by antibiotics poses a significant threat to human health and the ecosystem. Inspired from "Emmental Cheese" that owns lots of natural pores, we here fabricated a hierarchical cheese-like porous Spirulina residue biochar (KSBC) activated by KHCO₃ for efficiently boosting the removal of sulfathiazole (STZ). Through learning form nature that the CO₂ produced by bacteria can serve as the natural pore maker (like cheese-making), KHCO₃ was thus selected as the gas generating agent in this study. The effect of adding KHCO₃ on the surface properties of KSBC was comprehensively investigated. Benefiting from the activation, the KSBC with the mass ratio of 2:1 (2K-SBC) possessed the largest specific surface areas (1100 m² g^-1), which was approximately 81 times that of the original (not activated) Spirulina residue biochar (SBC) (13.56 m² g^-1). Moreover, 2K-SBC exhibited the maximum adsorption capacity for STZ (218.4 mg g^-1), dramatically higher than the SBC (25.78 mg g^-1). The adsorption kinetics and adsorption isotherms exhibited that the adsorption behavior of 2K-SBC for STZ was consistent with the pseudo-second-order and Langmuir models. Additionally, the adsorption thermodynamics revealed that the adsorption of STZ on 2K-SBC was spontaneous and exothermic. The pore-filling and electrostatic interaction were considered the main mechanism for the adsorption of STZ on 2K-SBC, whereas the π-π electron donor-acceptor (EDA) interaction and hydrogen bond would also partially contribute to the adsorption process.

Quantifying the contribution rates of sulfonamide antibiotics removal mechanisms in constructed wetlands using multivariate statistical analysis

The removal of antibiotics in subsurface flow constructed wetlands is performed through various removal mechanisms, such as adsorption, hydrolysis, microbial degradation and plant uptake. However, the contribution rates of the removal mechanisms in constructed wetlands are still not well studied. This study conducted a series of experiments and used multivariate statistical analysis to determine contribution rates for substrate adsorption, hydrolysis, and microbial degradation. Multiple stepwise regression analysis indicated that specific surface area and salt content were the main factors influencing sulfonamide adsorption, while temperature and pH were the main factors influencing sulfonamide hydrolysis. Variance partitioning analysis showed that the influence of physical-chemical factors was greater than that of nutrients on the microbial community. Partial least squares path analysis showed that the path coefficients of microbial degradation, adsorption and hydrolysis for sulfonamides removal in vertical subsurface flow constructed wetlands were 0.6339, 0.3608 and 0.0351, respectively, while the corresponding path coefficient were 0.5658, 0.4707 and 0.1079 in horizontal subsurface flow constructed wetlands, respectively. This means that microbial degradation contributes the most to the removal of sulfonamides in subsurface flow constructed wetlands. Enhanced microbial degradation may be a powerful measure to improve the removal of sulfonamides. These results will be helpful for understanding the removal mechanism of antibiotics and will provide a definite direction for pertinently improving sulfonamide removal efficiency in constructed wetlands.