Metagenomics Disentangles Differential Resistome Traits and Risks in Full-Scale Anaerobic Digestion Plants under Ambient, Mesophilic, and Thermophilic Conditions

Anaerobic digestion
(AD) systems are vital for converting organic
waste to green bioenergy but also serve as a non-negligible environmental
reservoir for antibiotic-resistance genes (ARGs) and resistant bacteria
of environmental and human health concerns. This study profiles the
antibiotic resistome of 90 full-scale biogas reactors and reveals
that AD microbiomes harbor at least 30 types and 1257 subtypes of
ARGs, of which 16% are located on plasmids showing potential mobility.
The total abundance of AD-ARGs ranges widely from 0.13 to 7.81 copies
per cell and is distributed into 42–739 subtypes, significantly
influenced (P < 0.05) by operational conditions
like digestion temperature and substrate types. Compared with the
ambient and mesophilic digesters, the thermophilic digesters harbor
a significantly lower abundance and diversity as well as greatly reduced
mobility and host pathogenicity levels (all P <
0.05) of ARGs, revealing that a higher digestion temperature mitigates
the overall resistome risks. The comprehensive analysis of basic traits
and key traits of the AD resistome is demonstrated to provide crucial
quantitative and qualitative insights into the diversity, distribution
pattern, and health risks of ARGs in full-scale AD systems. The revealed
knowledge offers new guidance for improving environmental resistome
management and developing oriented mitigation strategies to minimize
the unwanted spread of clinically important antimicrobial resistance
from AD systems.