Ferric chloride further simplified the horizontal gene transfer network of antibiotic resistance genes in anaerobic digestion

Fe oxides nano-modified pumice enhances hydrogenotrophic methanogenesis in anaerobic digestion: Performance and mechanism of microbial community

Anaerobic digestion (AD), as an eco-friendly biological process, shows potential for the decomposition of leachate produced by waste incineration power plants. In this study, the effects of Fe oxides nano-modified pumice (FNP) were investigated on the fresh leachate AD process. Firstly, a simple hydrothermal method was used to prepare FNP, then introduced into the UASB reactor to evaluate its AD efficiency. Results showed that the inclusion of FNP could shorten the lag phase by 10 days compared to the control group. Furthermore, cumulative methane production in the FNP group was enhanced by 20.11%. Mechanistic studies suggested that hydrogenotrophic methanogenesis in the FNP group was more pronounced due to the influence of key enzymes (i.e., dehydrogenase and coenzyme F420). Microbial community analysis demonstrated that FNP could enhance the abundance of Methanosarcina, Proteobacteria, Sytrophomonas, and Limnobacter, which might elevate enzyme activity involved in methane production. These findings suggest that FNP might mediate interspecies electron transfer among these microorganisms, which is essential for efficient leachate treatment.

Particle size transfer of antibiotic resistance genes in typical processes of municipal wastewater treatment plant

Occurrence and transfer of antibiotic resistance genes (ARGs) was investigated concerning sludge particle size in a typical wastewater treatment plant, and the roles of vertical (VGT) and horizontal gene transfer (HGT) in the spread of ARGs were explored. Results showed that although membrane bioreactor (MBR) effectively reduced the relative abundance of ARGs in the water phase, it concurrently enriched ARGs in MBR sludge, particularly for the largest-size particles (>150 μm). A decreasing trend in the relative abundance of ARGs was observed along with the decrease of sludge particle size, and larger-size particle sludge (>106 μm) formed a relatively stable composition of ARGs, while ARGs on smaller-size particle sludge (6.5-106 μm) fluctuate rapidly. Particle size does not affect the abundance distribution patterns or assembly mechanisms of ARGs as deterministic processes. The smallest-size particles were the primary attachment site for bacterial pathogens with highest diversity. Larger-size particle sludge (>106 μm) showed higher frequency of HGT, with Proteobacteria as the dominant hosts for this process.

Riverine antibiotic resistome along an anthropogenic gradient

The introduction of antibiotic-resistant bacteria into riverine systems through the discharge of wastewater treatment plant (WWTP) effluent and agricultural waste poses significant health risks. Even when not pathogenic, these bacteria can act as reservoirs for antibiotic resistance genes (ARGs), transferring them to pathogens that infect humans and animals. In this study, we used fluorescence in situ hybridization, qPCR, and metagenomics to investigate how anthropogenic activities affect microbial abundance and the resistome along the Holtemme River, a small river in Germany, from near-pristine to human-impacted sites. Our results showed higher bacterial abundance, a greater absolute and relative abundance of ARGs, and a more diverse ARG profile at the impacted sites. Overall, the ARG profiles at these sites reflected antibiotic usage in Germany, with genes conferring resistance to drug classes such as beta-lactams, aminoglycosides, folate biosynthesis inhibitors, and tetracyclines. There were also variations in the ARG profiles of the impacted sites. Notably, there was a high abundance of the oxacillin resistance gene OXA-4 at the downstream site in the river. In the metagenome assembly, this gene was associated with a contig homologous to small plasmids previously identified in members of the Thiotrichaceae. The likely in-situ host of the putative plasmid was a close relative of Thiolinea (also known as Thiothrix) eikelboomii, a prominent member of WWTP microbiomes worldwide. Our results show that the effluent from WWTPs can introduce bacteria into the environment that act as shuttle systems for clinically relevant ARG.

Enhancement of anaerobic treatment of antibiotic pharmaceutical wastewater through the development of iron-based and carbon-based materials: A critical review

The extensive use of antibiotics has created an urgent need to address antibiotic wastewater treatment, posing significant challenges for environmental protection and public health. Recent advances in the efficacy and mechanisms of conductive materials (CMs) for enhancing the anaerobic biological treatment of antibiotic pharmaceutical wastewater are reviewed. For the first time, the focus is on the various application forms of iron-based and carbon-based CMs in strengthening the anaerobic methanogenic system. This includes the use of single CMs such as zero-valent iron (ZVI), magnetite, biochar (BC), activated carbon (AC), and graphene (GP), as well as iron-based and carbon-based composite CMs with diverse structures. These structures include mixed, surface-loaded, and core-shell combinations, reflecting the development of CMs. Iron-based and carbon-based CMs promote the rapid removal of antibiotics through adsorption and enhanced biodegradation. They also mitigate the inhibitory effects of toxic pollutants on microbial activity and reduce the expression of antibiotic resistance genes (ARGs). Additionally, as effective electron carriers, these CMs enrich microorganisms with direct interspecies electron transfer (DIET) functions, accelerate interspecies electron transfer, and facilitate the conversion of organic matter into methane. Finally, this review proposes the use of advanced molecular detection technologies to clarify microbial ecology and metabolic mechanisms, along with microscopic characterization techniques for the modification of CMs. These methods can provide more direct evidence to analyze the mechanisms underlying the cooperative anaerobic treatment of refractory organic wastewater by CMs and microorganisms.

Antibiotic fermentation residue for biohydrogen production: Inhibitory mechanisms of the inherent antibiotic

Antibiotic fermentation residue, which is generated from the microbial antibiotic production process, has been a troublesome waste faced by the pharmaceutical industry. Dark fermentation is a potential technology to treat antibiotic fermentation residue in terms of renewable H2 generation and waste management. However, the inherent antibiotic in antibiotic fermentation residue may inhibit its dark fermentation performance, and current understanding on this topic is limited. This investigation examined the impact of the inherent antibiotic on the dark H2 fermentation of Cephalosporin C (CEPC) fermentation residue, and explored the mechanisms from the perspectives of bacterial communities and functional genes. It was found that CEP-C in the antibiotic fermentation residue significantly inhibited the H2 production, with the H2 yield decreasing from 17.2 mL/g-VSadded to 12.5 and 9.6 mL/g-VSadded at CEP-C concentrations of 100 and 200 mg/L, respectively. CEP-C also prolonged the H2-producing lag period. Microbiological analysis indicated that CEP-C remarkably decreased the abundances of high-yielding H2-producing bacteria, as well as downregulated the genes involved in hydrogen generation from the"pyruvate pathway" and"NADH pathway", essentially leading to the decline of H2 productivity. The present work gains insights into how cephalosporin antibiotics influence the dark H2 fermentation, and provide guidance for mitigating the inhibitory effects.

Coagulation promotes the spread of antibiotic resistance genes in secondary effluents

Wastewater treatment plants (WWTPs) are biological hotspots receiving the residual antibiotics and antibiotic resistant bacteria/genes (ARB/ARGs) that greatly influence the spread of antibiotic resistance in the environment. A common method used in WWTPs for the purification of secondary effluent is coagulation. Notwithstanding the increasing health concern of antibiotic resistance in WWTPs, the impact of coagulation on the emergence and spread of antibiotic resistance remains unclear. To shed light on this, our study investigated the behavior of four representative ARB types (tetracycline, sulfamethoxazole, clindamycin, and ciprofloxacin resistance) during the coagulation process in a model wastewater treatment plant. Our search showed a significant reduction in the presence of ARBs after either PAC or FeCl3 coagulation, with removal efficiencies of 95% and 90%, respectively. However, after 4 days of storage, ARB levels in the coagulated effluent increased by 6-138 times higher than the original secondary effluent. It suggests a potential resurgence and spread of antibiotic resistance after coagulation. Detailed studies suggest that coagulants, particularly PAC, may facilitate the transfer of ARGs among different bacterial species by the enhanced cell-cell contact during coagulation-induced bacterial aggregation. This transfer is further enhanced by the factors such as auxiliary mixing, longer incubation time and ideal operating temperatures. In addition, both PAC and FeCl3 affected gene expression associated with bacterial conjugation, leading to an increase in conjugation efficiency. In conclusion, while coagulation serves as a purification method, it might inadvertently boost the spread of ARGs during tertiary wastewater treatment. This underscores the importance of implementing subsequent measures to mitigate this effect. Our findings provide a deeper understanding of the challenges posed by bacterial antibiotic resistance in wastewater and pave the way for devising more effective ARB and ARG management strategies.

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Attenuation effects of ZVI/PDS pretreatment on propagation of antibiotic resistance genes in bioreactors: Driven by antibiotic residues and sulfate assimilation

Sulfate radical-based advanced oxidation processes (AOPs) combined biological system was a promising technology for treating antibiotic wastewater. However, how pretreatment influence antibiotic resistance genes (ARGs) propagation remains largely elusive, especially the produced by-products (antibiotic residues and sulfate) are often ignored. Herein, we investigated the effects of zero valent iron/persulfate pretreatment on ARGs in bioreactors treating sulfadiazine wastewater. Results showed absolute and relative abundance of ARGs reduced by 59.8%- 81.9% and 9.1%- 52.9% after pretreatments. The effect of 90-min pretreatment was better than that of the 30-min. The ARGs reduction was due to decreased antibiotic residues and stimulated sulfate assimilation. Reduced antibiotic residues was a major factor in ARGs attenuation, which could suppress oxidative stress, inhibit mobile genetic elements emergence and resistant strains proliferation. The presence of sulfate in influent supplemented microbial sulfur sources and facilitated the in-situ synthesis of antioxidant cysteine through sulfate assimilation, which drove ARGs attenuation by alleviating oxidative stress. This is the first detailed analysis about the regulatory mechanism of how sulfate radical-based AOPs mediate in ARGs attenuation, which is expected to provide theoretical basis for solving concerns about by-products and developing practical methods to hinder ARGs propagation.

Electron shuttles enhanced the removal of antibiotics and antibiotic resistance genes in anaerobic systems: A review

The environmental and epidemiological problems caused by antibiotics and antibiotic resistance genes have attracted a lot of attention. The use of electron shuttles based on enhanced extracellular electron transfer for anaerobic biological treatment to remove widespread antibiotics and antibiotic resistance genes efficiently from wastewater or organic solid waste is a promising technology. This paper reviewed the development of electron shuttles, described the mechanism of action of different electron shuttles and the application of enhanced anaerobic biotreatment with electron shuttles for the removal of antibiotics and related genes. Finally, we discussed the current issues and possible future directions of electron shuttle technology.