Prioritized regional management for antibiotics and heavy metals in animal manure across China

Effects of rhamnolipid replacement of chlortetracycline on growth performance, slaughtering traits, meat quality and antioxidant function in broilers

BACKGROUND

Rhamnolipids (RLS) are surfactants that improve the growth performance of poultry by improving the absorption of nutrients. This study aims to investigate the effects of RLS replacement of chlortetracycline (CTC) on growth performance, slaughtering traits, meat quality, antioxidant function and nuclear-factor-E2-related factor 2 (Nrf2) signaling pathway in broilers. A total of 600 one-day-old Arbor Acres chicks were randomly assigned to five groups with eight replicates in each group, raised for 42 days. Broilers were respectively fed a basal diet with no CTC or RLS, 75 mg kg-1 CTC, and 250, 500, 1000 mg kg-1 RLS.

RESULTS

Dietary supplementation with RLS linearly increased the average daily gain, average daily feed intake, carcass yield, eviscerated yield, ether extract, enhanced total superoxide and glutathione peroxidase (GPx) activities, overexpressed the relative expressions of Nrf2, heme oxygenase 1, Copper/zinc superoxide dismutase, Manganese superoxide dismutase, GPx and catalase and decreased the lightness value at 24 h, drip loss and malondialdehyde contents of broilers (P < 0.05). Compared with the control group, broilers fed 1000 mg kg-1 RLS reduced the drip loss and broilers fed 500 mg kg-1 RLS increased muscle crude fat content (P < 0.05). Compared with the CTC group, dietary supplementation with 1000 mg kg-1 RLS increased eviscerated yield (P < 0.05).

CONCLUSION

RLS could improve growth performance, crude fat content, meat quality and antioxidant capacity and activate relative expression of genes in the Nrf2 signaling pathway in broilers. It could be used as an antibiotic substitute in diets and the recommended supplemental dose of RLS in feed of broilers is 1000 mg kg-1. © 2024 Society of Chemical Industry.

Luminescent iron phthalocyanine organic polymer nanosheets with space-separated dual-active sites for the detection and photocatalytic reduction of Cr(Ⅵ) from wastewater

Cr(Ⅵ) residues in livestock and poultry wastewater are a rising concern for human health and biotic environments. For the removal of Cr(Ⅵ), its simultaneous reduction and adsorption represents a sustainable and efficient strategy. Herein, iron nodes on covalently bonded two-dimensional phthalocyanine organic polymer (PcOP-Fe) nanosheets with space-separated dual-active sites are developed for the simultaneous detection and removal of Cr(VI) from wastewater. In the FeN4 structure of PcOP-Fe nanosheets, Fe acts as an electron capture center, effectively facilitating the accumulation of photogenerated electrons and transferring them to Cr(VI), thereby achieving its photocatalytic reduction. Meanwhile, pyrrolic nitrogen provides excellent adsorption sites, enabling the adsorption of Cr(III) or Cr(0). Fe accumulates the photogenerated electrons from pyrrole N and transfer them to Cr(Ⅵ). The formation of N-Cr(Ⅲ) bonds causes a space-separation between Cr(Ⅵ) and Cr(III). In addition, PcOP-Fe can be used for a Cr(Ⅵ) detection agent. The photoluminescence intensity decreases linearly with increasing Cr(Ⅵ) concentration from 80 μM to 2 mM, with a limit of detection of 0.18 μM. The PcOP-Fe nanosheets exhibit good Cr(Ⅵ) detection and reduction performance in livestock and poultry wastewater, suggesting their suitability for practical sensing applications. Thus, the PcOP-Fe nanosheets with space-separated dual-active sites are promising for the simultaneous detection and removal of Cr(Ⅵ) in water treatment processes.

Comparative efficacy of anaerobic digestion systems in removing antimicrobial resistance genes from swine wastewater

Swine farm wastewater is a major reservoir of antimicrobial resistance genes (ARGs). Anaerobic digestion (AD), widely implemented in farms, has been extensively studied for ARG removal. However, a comparative study on ARG removal efficiency across the four principal AD systems - up-flow anaerobic sludge blanket (UASB), continuous stirred tank reactor (CSTR), buried biogas digester (BBD), and septic tank (SPT) - is lacking. Herein, we employed metagenomic sequencing, ultra-performance liquid chromatography-tandem mass spectrometry, as well as atomic absorption spectrometry/atomic fluorescence spectrophotometry, and revealed that UASB and CSTR achieved higher removal efficiencies for both ARGs (67% and 57%) and antibiotic residues (100% and 90%) compared to BBD and SPT. Acinetobacter, Escherichia, Pseudomonas and Streptococcus were the primary ARG hosts, comprising over 65% of the total abundance in influent samples. UASB and CSTR systems demonstrated superior removal efficiencies for both mobile genetic elements (MGEs) and antibiotic residues, both of which had essential impacts on ARG profiles. In addition, heavy metals might contribute to variation in ARGs through horizontal gene transfer. Collectively, the variation in microbial communities and better removal of both MGEs and antibiotic residues contribute to the remarkable ARG removal efficiency of UASB and CSTR, therefore, advocating for the widespread adoption of these two AD systems in swine farms.

Insights into the interactions of plant-associated bacteria and their role in the transfer of antibiotic resistance genes from soil to plant

This study discussed the role of plant-associated microbiome in regulating ARG transfer in soil-plant systems. Results showed that target ARGs in plants were mainly derived from rhizosphere soil. Cooperative interactions among bacteria in rhizosphere soil, plant-roots, plant-shoots, and soil-roots-shoots systems occurred during ARG transfer. The number of modules and keystone taxa identified as positively correlated with ARG transfer in rhizosphere soil, roots, and shoots was 3 and 49, 3 and 41, 2 and 5, respectively. Among these modules, module 3 in roots was significantly positively correlated with module 3 in rhizosphere soils and module 2 in shoots, indicating that module 3 in roots played central hub roles in ARG transfer from rhizosphere soil to roost and shoots. This may be because module 3 in roots increased cell motility and xenobiotics biodegradation and metabolism. These keystone taxa mainly belonged to Proteobacteria that can carry ARGs to transfer in soil-plant systems, especially Clostridium-sensu_stricito and Pseudomonas in rhizosphere soil carried ARGs into the shoot. Additionally, they promoted ARG transfer by increasing plant biomass, net photosynthetic rate and water use efficiency. The findings helped reveal the mechanism of plant-associated bacterial interactions and provided understanding for potential risks of ARG transfer from soil to plants.

Rational design of a dual-bacterial system for synchronous removal of antibiotics and Pb(Ⅱ)/Cd(Ⅱ) from water

Facing the combined pollution of antibiotics and heavy metals caused by livestock excrement and industrial effluents, how to use microbial technology to remove these pollutants simultaneously is an important research topic in environmental remediation. In addition, quick separation of the bacteria-water after remediation is also an urgent problem. In this study, we gradually developed a dual-bacteria microbial treatment technology capable of removing Pb(Ⅱ), Cd(Ⅱ) and common antibiotics, as well as self-settling after treatment. The key technology in this study mainly includes modifying the bacterial membrane proteins using Pb-binding protein PbrR, Cd-binding protein CadR and bacterial laccase CotA via surface-display technology to maximize the removal of Pb(Ⅱ), Cd(Ⅱ) and antibiotics, separately. Besides, the introduction of nanobody-antigen adhesion facilitated the self-settling in dual-bacterial system. Then, we studied its effectiveness in removing single pollutants, analyzed the influence of different heavy metal ions, and conducted detailed studies on the kinetics. Further characterization of heavy metal biosorption behavior was conducted using SEM, SEM-EDS, FTIR, and XPS techniques. Via protein fusion and dual vector expression, we constructed a dual-bacteria treatment system that could achieve rapid, selective removal of combined pollutants at a wide pH range temperature range, ultimately precipitating at bottom. Finally, molecular dynamics simulation was employed to elucidate the molecular mechanism underlying the selective biosorption by metal-binding proteins. The findings in this study hold significant implications for achieving selective pollutant removal using engineering bacteria in complex water environments.

Unraveling the role of black soldier fly larvae in chicken manure conversion: Facilitating maturation and enhancing humification

Black soldier fly larvae (BSFL) have garnered considerable attention for their efficacy in mitigating waste management challenges. However, their potential in treating antibiotics contaminated chicken manure remains uncertain. This study investigates the physicochemical properties changes and nutrient dynamics during the composting of contaminated-chicken manure using BSFL. The results indicate that BSFL treatment reduces electrical conductivity (by 6.01-58.09 %), organic matter, and dissolved organic carbon content in chicken manure throughout the composting process, while maintaining a more stable pH value (pH ∼ 6.0-8.0). This is attributed to the consumption of organic matter by BSFL and the subsequent promotion of organic acid formation. Additionally, BSFL treatment improves the degree of aromatization of dissolved organic matter (DOM) in chicken manure and increases the proportions of fulvic acid (up to 48.77 %) and humic acid (maximally 14.27 %) within the DOM. The germination index and pot experiments indicated improved compost maturity and plant growth in BSFL-treated composts. Furthermore, BSFL meal demonstrated high protein and essential fatty acid content, highlighting its potential as a protein supplement in animal feed. This study underscores the efficacy of BSFL in enhancing compost quality and nutrient availability, offering a sustainable solution for waste management and animal feed production.

Spatial and Bioaccumulation of Heavy Metals in a Sheep-Based Food System: Implications for Human Health

Heavy metal contamination in agricultural soils presents serious environmental and health risks. This study assessed the bioaccumulation and spatial distribution of nickel, cadmium, zinc, lead, and copper within a sheep-based food chain in the Baia Mare region, Romania, which includes soil, green grass, sheep serum, and dairy products. Using inductively coupled plasma mass spectrometry (ICP-MS), we analyzed the concentrations of these metals and calculated bioconcentration factors (BCFs) to evaluate their transfer through trophic levels. Spatial analysis revealed that copper (up to 2528.20 mg/kg) and zinc (up to 1821.40 mg/kg) exceeded permissible limits, particularly near former mining sites. Elevated lead (807.59 mg/kg) and cadmium (2.94 mg/kg) were observed in industrial areas, while nickel and cobalt showed lower concentrations, but with localized peaks. Zinc was the most abundant metal in grass, while cadmium transferred efficiently to milk and cheese, raising potential health concerns. The results underscore the complex interplay between soil properties, contamination sources, and biological processes in heavy metal accumulation. These findings highlight the importance of continuous monitoring, risk assessment, and mitigation strategies to protect public health from potential exposure through contaminated dairy products.

Mitigating Tetracycline antibiotic contamination in chicken manure using ex situ fermentation system

Excessive use of tetracycline antibiotics in poultry farming results in significant concentrations of these drugs and tetracycline resistance genes (TRGs) in chicken manure, impacting both environmental and human health. Our research represents the first investigation into the removal dynamics of chlortetracycline (CTC) and TRGs in different layers of an ex situ fermentation system (EFS) for chicken waste treatment. By pinpointing and analyzing dominant TRGs-harboring bacteria and their interactions with environmental variables, we've closed an existing knowledge gap. Findings revealed that CTC's degradation half-lives spanned 3.3-5.8 days across different EFS layers, and TRG removal efficiency ranged between 86.82% and 99.52%. Network analysis highlighted Proteobacteria and Actinobacteria's essential roles in TRGs elimination, whereas Chloroflexi broadened the potential TRG hosts in the lower layer. Physical and chemical conditions within the EFS influenced microbial community diversity, subsequently impacting TRGs and integrons. Importantly, our study reports that the middle EFS layer exhibited superior performance in eliminating CTC and key TRGs (tetW, tetG, and tetX) as well as intI2. Our work transcends immediate health and environmental remediation by offering insights that encourage sustainable agriculture practices.

Pollution levels and potential ecological risks of trace elements in relation to bacterial community in surface water of shallow lakes in northern China before and after ecological water replenishment

Ecological water replenishment is a crucial and effective measure to improve the water quality and ecological function of lakes. However, the effects of ecological water replenishment on the pollution characteristics and ecological risks of trace elements and bacterial communities in lake surface water are still kept unclear. We investigated the pollution levels and potential ecological risks for trace elements, as well as variation of the bacterial community in surface water in the BYD lake before and after ecological water replenishment. Our results revealed that higher levels and pollution indexes (Igeo) of trace metals (e.g., As, Cd, Co, Cu and Ni; p < 0.05) after ecological water replenishment were observed than before ecological water replenishment and their total potential ecological risk (∑RI) were increased. In contrast, the network complexity of these trace elements, including nodes, edges, average diameter, modularity, clustering coefficient and average pathlength showed a decrease after ecological water replenishment than before. The diversity (community richness, community diversity and phylogenetic diversity decreased) and community structure of the bacterial community in the surface water (p < 0.05) were greatly changed after ecological water replenishment than before, with the increase in heavy metal-resistant phylum (e.g., Acidobacteriota). Moreover, the concentration of trace elements and ∑RI were significantly correlated with the alpha diversity of bacterial community, as well as dissolved organic carbon (DOC) and ORP, after ecological water replenishment. The findings indicate that it is very necessary to continuously monitor trace metal pollution levels and heavy metal-resistant phylum and identify their potential pollution sources for water environment control and lake ecosystem health.