Seasonal dynamics survey and association analysis of microbiota communities, antibiotic resistance genes distribution, and biotoxicities characterization in landfill-leachate

Objective: To reflect the potential and intrinsic association among microbiota structure, antibiotic resistance genes distribution and biological toxicity of landfill-leachate according to seasonal change, and accurately assess the potential threat of leachate to the surrounding environment.Methods: On the basis of the leachate water quality monitoring data from January to December 2020, principal component analysis (PCA) was used to identify the main pollutants in the leachate; Vibrio fischeri luminescence inhibition test was used to detect the comprehensive biotoxicity of the leachate; 16S rDNA amplicon sequencing was used for leachate microbiota. q-PCR was used to detect the class 1 integron (intI1), and eight antibiotic resistance genes (sul1, sul2, tetA, tetB, tetM, tetQ, mefA, and mexF); Canonical correspondence (CCA) analysis was carried out for the association analysis.Result: The biotoxicity of leachate in the second quarter was the highest. The dominant phylum of leachate microbiota from 1st quarters to 4th quarters was Proteobacteria (94.97 %, 85.43 %, 88.20 %, and 84.11 %), and the dominant genera were Thiomonas (60.41 %, 26.83 %, 25.66 %, and 30.51 %), Pseudomonas (5.89 %, 1.86 %, 0.68 %, and 4.72 %), Desulfurella (8.52 %, 0.57 %, 3.81 %, and 8.25 %), and Acidithiobacillus (4.71 %, 0.69 %, 0.87 %, and 5.91 %); Nitrospirillum was negatively correlated with chemical oxygen demand (COD) (R=-0.561, P = 0.008) and five-day biochemical oxygen demand (BOD5) (R=-0.591, P = 0.005); Limnohabitans was posi-tively correlated with pH (R=0.444, P = 0.044). Four AR genes (sul1, sul2,tetM, and tetQ) were detected in all the samples, while the second quarter had the highest concentration of sul1(6.31 +/- 0.49 lg copies/ng DNA), tetM (3.01 +/- 1.38 lg copies/ng DNA) and tetQ (3.64 +/- 0.90 lg copies/ng DNA).Conclusion: As the mature landfill, the quality of this leachate met the pollution control standards for domestic waste landfills. Thiomycetes, Pseudomonas, Desulfurization, and Thiopterus acidophyllum constitute the dominant microbiota. However, leachate in the second quarter had more serious contamination, the higher biotoxicity, higher concentration of AR genes, together with higher microbiota richness and diversity, which deserved more attention for the potential threat to the surrounding environment.

Automated summary

This study aimed to accurately assess the potential threat of landfill-leachate to the surrounding environment by investigating the potential association among microbiota structure, antibiotic resistance genes distribution, and biological toxicity of landfill-leachate according to seasonal change. The results showed that leachate in the second quarter had the highest biotoxicity, and the dominant microbiota consisted of Proteobacteria and several genera with antibiotic resistance genes. These findings highlight the potential threat of leachate to the surrounding environment and call for more attention.