Distribution of extracellular and intracellular antibiotic resistance genes in sludge fractionated in terms of settleability

Wenjiao Li; Haoning Su; Jiefeng Li; Sartaj Ahmad Bhat; Guangyu Cui; Zaw Min Han; Diva Sagita Nadya; Yongfen Wei; Fusheng Li

doi:10.1016/j.scitotenv.2020.143317

Distribution of extracellular and intracellular antibiotic resistance genes in sludge fractionated in terms of settleability

Sci Total Environ. 2021 Mar 15:760:143317. doi: 10.1016/j.scitotenv.2020.143317. Epub 2020 Nov 12.

Authors

Wenjiao Li¹, Haoning Su², Jiefeng Li³, Sartaj Ahmad Bhat⁴, Guangyu Cui⁵, Zaw Min Han¹, Diva Sagita Nadya², Yongfen Wei⁴, Fusheng Li⁶

Affiliations

¹ Graduate School of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
² Graduate School of Natural Science and Technology, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
³ Department of Architecture, Lu Liang University, Lishi, Shanxi 033000, China.
⁴ River Basin Research Center, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan.
⁵ State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, Shanghai 200092, China.
⁶ Graduate School of Engineering, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; Graduate School of Natural Science and Technology, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; River Basin Research Center, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan; School of Environment and Energy, South China University of Technology, Guangzhou 510006, China. Electronic address: lifs@gifu-u.ac.jp.

PMID: 33223182
DOI: 10.1016/j.scitotenv.2020.143317

Abstract

The widespread proliferation of antibiotic resistance genes (ARGs) is a serious environmental and human health issue. Wastewater treatment facilities (WWTFs) are potential sources to spread ARGs to natural environment, for which, the presence state of ARGs in the sludge, as extracellular ones (eARGs) or intracellular ones (iARGs), along with the sludge settleability, are very important factors. The sludge settleability is closely associated with its floc size and density, bacterial activity, and the proportion of intact/damaged bacterial cells that aggregate together to form flocs for separation in the sedimentation process. It is reasonable to hypothesize that the distribution of eARGs and iARGs may differ with the sludge fractions of different settleability, a topic of great academic and practical significance requiring clarification. In this study, sludge samples from the aerobic contact tank of six household WWTFs were fractionated into fractions with different settling velocities: sludge of low settleability (LS), medium settleability (MS) and high settleability (HS); and the distribution of eARGs and iARGs in the obtained fractions for the widely detected tet G, tet M and sul 1 in water environment was evaluated based on the PMA-qPCR method, together with the evaluation for the well reported mobile genomic element intl 1 and total bacterial 16S rDNA. For the LS fractions, which contained more damaged bacterial cells, the distribution percentages of eARGs were generally higher than those of iARGs. For the HS fractions, which contained flocs with larger sizes formed by both intact and damaged bacterial cells, the relative abundances of ARGs and intl 1 were found apparently lower even if the presence percentages of eARGs were comparatively higher. It is thus inferable that sludge fractions of LS may possess higher transfer potential for ARGs and enhancing their settleability through optimization of the operation conditions is important for mitigating the proliferation of ARGs.

Keywords: Activated sludge; Antibiotic resistance genes; Bacteria; Mobile genetic element; Settleability; Wastewater.

MeSH terms

Anti-Bacterial Agents* / pharmacology
Drug Resistance, Microbial / genetics
Genes, Bacterial
Humans
Sewage*
Wastewater

Substances

Anti-Bacterial Agents
Sewage
Waste Water