Thermophilic rather than mesophilic sludge anaerobic digesters possess lower antibiotic resistant genes abundance

[Display omitted] •Sludge ARGs, plasmid ARGs, and cell-free ARGs in sludge AD were investigated.•Thermophilic AD removed 2 logs more sludge and plasmid ARGs than mesophilic AD.•The abundance of cell-free ARGs in thermophilic and mesophilic AD were similar.•Firmicutes might be a main group of potential hosts of ARGs in sludge AD. For exploring the impact of temperature on antibiotic resistant genes (ARGs) during sludge anaerobic digestion (AD), the dynamic variations of sludge ARGs, plasmid ARGs, and cell-free ARGs in mesophilic (25 °C and 35 °C) and thermophilic (55 °C) digesters were investigated. The study revealed that the abundance of sludge ARGs and plasmid ARGs in thermophilic sludge AD was significantly lower than that in mesophilic digesters, while the cell-free ARGs abundance of the thermophilic digesters was similar to mesophilic digesters. Higher archaea abundance, lower bacteria abundance, and different microbial community were found in thermophilic digesters compared to that of mesophilic ones. Firmicutes might be a main group of potential hosts of ARGs in sludge AD. The distinct microbial community was the main contributor to the low ARGs abundance in thermophilic sludge AD. Thermophilic operation at 55 °C rather than mesophilic operation is more conducive to control ARGs in sludge anaerobic digestion.