No abstract

Aquaculture sediments are a purported sizable pool of antibiotic resistance genes (ARGs). However, the pathways for transmission of ARGs from sediments to animals and humans remain unclear. We conducted an ARG survey in sediments from a bullfrog production facility located in Guangdong, China, and simulated zebrafish breeding systems were constructed, with or without biochar addition in sediments, to explore the effects of biochar on ARGs and their precursors of the sediment and zebrafish gut. After 60 days, 6 subtypes of ARGs and intI1 were detected, with sediments harboring more ARGs than zebrafish gut. The addition of biochar reduced the abundance of ARGs in the sediment and zebrafish gut, as well as suppressed the horizontal transmission of ARGs from sediment to zebrafish gut. Network analysis and partial least squares path modeling revealed that ARG enrichment was mainly affected by bacterial groups dominated by Nitrospirae, Gemmatimonades, Chloroflexi, and Cyanobacteria and intI1. Our findings provide insights into the transmission of ARGs from sediment to animals and highlight the efficacy of biochar amendments to aquaculture sediments to reduce the transmission of ARGs.

The relationship between biochar physicochemical characteristics and the adsorption and the degradation of extracellular DNA (eDNA) was studied to assess controls on the fate and transport of eDNA in the environment. Biochar samples were generated by pyrolysis of Chinese herbal medicine residues of sweet wormwood ( Artemisia annua L.) at 500, 600, and 700 °C. Selected physicochemical properties of the biochar were characterized. Adsorption dynamics (adsorption capacity and kinetics) of eDNA to biochar were quantified using several adsorption kinetic and isotherm models. Furthermore, gel electrophoresis was used to detect the impact of biochar on the degradation of eDNA by DNase I. Characterization results indicated that biochar generated from Chinese herbal medicine residues was dominantly aromatic, stable, and polar. Adsorption data showed that the biochar–eDNA interactions were dominated by an electrostatic interaction mechanism. Based on eDNA adsorption capacity and gel electrophoresis of eDNA fragments, we demonstrated that larger eDNA fragments were adsorbed to the biochar and protected from degradation by DNase I. The Chinese herbal medicine residues generated a superior biochar product to adsorb eDNA and protect it from degradation by DNase I. The results of this study provide a mechanistic understanding of factors controlling the fate and transport of eDNA in the environment.

A two-chamber slurry microbial fuel cell (SMFC) was constructed using black-odorous river sediments as substrate for the anode. We tested addition of potassium ferricyanide (K 3 [Fe(CN) 6 ]) or sodium chloride (NaCl) to the cathode chamber (0, 50, 100, 150, and 200 mM) and aeration of the cathode chamber (0, 2, 4, 6, and 8 h per day) to assess their response on electrical generation, internal resistance, and methane emission over a 600-h period. When the aeration time in the cathode chamber was 6 h and K 3 [Fe(CN) 6 ] or NaCl concentrations were 200 mM, the highest power densities were 6.00, 6.45, and 6.64 mW•m −2 , respectively. With increasing K 3 [Fe(CN) 6 ] or NaCl concentration in the cathode chamber, methane emission progressively decreased (mean ± SD: 181.6 ± 10.9 → 75.5 ± 9.8 mg/m 3 •h and 428.0 ± 28.5 → 157.0 ± 35.7 mg/m 3 •h), respectively, but was higher than the reference having no cathode/anode electrodes (~ 30 mg/m 3 •h). Cathode aeration (0 → 8 h/day) demonstrated a reduction in methane emission from the anode chamber for only the 6-h treatment (mean: 349.6 ± 37.4 versus 299.4 ± 34.7 mg/m 3 •h for 6 h/day treatment); methane emission from the reference was much lower (85.3 ± 26.1 mg/m 3 •h). Our results demonstrate that adding an electron acceptor (K 3 [Fe(CN) 6 ]), electrolyte solution (NaCl), and aeration to the cathode chamber can appreciably improve electrical generation efficiency from the MFC. Notably, electrical generation stimulates methane emission, but methane emission decreases at higher power densities.