Deciphering antibiotic resistome variations during nitrogen removal process transition under mixed antibiotics stress: Assembly process and driving factors

Resistance induction potency assessment of antibiotic production wastewater and associated resistome shaping mechanisms

Antibiotic production wastewater (APW) contains multiple substances known to select for and facilitate horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs); however, whether these substances can induce the evolution of antibiotic resistance in real wastewater environments and the fate of such resistance induction potency during the treatment process are poorly understood, nor are its relationship with wastewater quality parameters and function in shaping the antibiotic resistome. In this study, the impacts of filter-sterilized APW and municipal wastewater on the resistance selection of Escherichia coli and the transfer dynamics of conjugative RP4 plasmid-borne ARGs across indigenous sludge communities were evaluated. The resistance development and transfer processes were accelerated in APW owing to enhanced growth inhibition, oxidative stress, and membrane permeability, with antibiotic concentrations much lower than their minimum inhibition concentrations. The effects were reduced simultaneously with the removal of COD and NH3N, but APW effluents still exhibited significant resistance induction potency with wastewater quality parameters meeting discharge standards. In contrast, municipal wastewater did not result in any detectable changes. Based on the metagenomic assembly and binning, stronger resistance induction potency in the antibiotic production wastewater treatment plant endowed indigenous sludge and effluent with greater accumulation, genetic mobility, and pathogenic accessibility of ARGs than in the municipal wastewater treatment plant. Antibiotic resistome assembly was determined primarily by deterministic processes, driven jointly by resistance induction potency, mobilome variance, and microbiome shifts. These results provide novel insights into the application of bioassays to comprehensively evaluate the antibiotic resistance induction effects of APW and their relationships with the resistome to manage risks during the treatment process.

Unraveling the effects and mechanisms of antibiotics on aerobic simultaneous nitrogen and phosphorus removal by Acinetobacter indicus CZH-5

The effects of antibiotics, such as tetracycline, sulfamethoxazole, and ciprofloxacin, on functional microorganisms are of significant concern in wastewater treatment. This study observed that Acinetobacter indicus CZH-5 has a limited capacity to remove nitrogen and phosphorus using antibiotics (5 mg/L) as the sole carbon source. When sodium acetate was supplied (carbon/nitrogen ratio = 7), the average removal efficiencies of ammonia-N, total nitrogen, and orthophosphate-P increased to 52.46 %, 51.95 %, and 92.43 %, respectively. The average removal efficiencies of antibiotics were 84.85 % for tetracycline, 39.32 % for sulfamethoxazole, 18.85 % for ciprofloxacin, and 23.24 % for their mixtures. Increasing the carbon/nitrogen ratio to 20 further improved the average removal efficiencies to 72.61 % for total nitrogen and 97.62 % for orthophosphate-P (5 mg/L antibiotics). Additionally, the growth rate and pollutant removal by CZH-5 were unaffected by the presence of 0.1-1 mg/L antibiotics. Transcriptomic analysis revealed that the promoted translation of aceE, aarA, and gltA genes provided ATP and proton -motive forces. The nitrogen metabolism and polyphosphate genes were also affected. The expression of acetate kinase, dehydrogenase, flavin mononucleotide enzymes, and cytochrome P450 contributed to antibiotic degradation. Intermediate metabolites were investigated to determine the reaction pathways.

Effect of Mn-HA on ARGs and MRGs in nitrogen-culturing sludge

The simultaneous escalation in ARGs (antibiotic resistance genes) and MRGs (metal resistance genes) further complicates the intricate network of factors contributing to the proliferation of microbial resistance. Manganese, which has been reported to affect the resistance of bacteria to antibiotics and metals, plays a vital role in microbial nitrogen metabolism. Moreover, nitrifying and denitrifying populations are potential hosts for ARGs. In this study, manganese was introduced in its prevalent organic chelated form in the environment (Manganese humus chelates, Mn-HA) to a N metabolism sludge to explore the effect of manganese on MRGs and ARGs dissemination. Metagenomics results revealed that manganese availability enhances nitrogen metabolism, while a decrease in ARGs was noted which may be attributed to the inhibition of horizontal gene transfer (HGT), reflected in the reduced integrase -encoded gene int. Population analysis revealed that nitrifier and denitrifier genus harbor MRGs and ARGs, indicating that nitrifier and denitrifier are hosts of MRGs and ARGs. This raises the question of whether the prevalence of ARGs is always increased in metal-contained environments.