Effects of higher temperature on antibiotic resistance genes for in-situ biogas upgrading reactors with H2 addition

In-situ biogas upgrading by H2 injection is a promising method for bio-natural gas production, yet the effect of H2 addition on antibiotic resistance genes during the in-situ biogas upgrading process remains unknown. We analyzed mesophilic and thermophilic in-situ biogas upgrading digesters with intermittent or continuous mixing models using metagenomic and metatranscriptomic methods to evaluate the effects of H2 addition on antibiotic resistance profiles. We found that H2 addition had less impact in the mesophilic reactor. In the thermophilic reactor, the influenced antibiotic resistance ontology (AROs) was mostly bound to the integral membrane transporters of the ATP-binding cassette and major facilitator superfamily. The annotated gene numbers of four drug classes, including macrolide, glycopeptide, lincosamide, and fluoroquinolone, increased distinctly after H2 addition. Acetate concentration is a vital indicator for distinguishing the abundance of different antibiotic efflux pumps. Most of the AROs influenced by Ruminiclostridium replaced the original dominant species Clostridium, and the versatile genus Methanosarcina was the sole methanogen correlated with the altered AROs of efflux pumps conferring antibiotic resistance. The introduced H2 was synthesized to CH4via the hydrogenotrophic pathway of Methanosarcina flavescens, and part of the consumed H2 was used for cell growth. [Display omitted] •Profile of AROs only significantly changed in thermophilic reactor after H2 added.•Influenced ARO terms were mostly fastened on the integral membrane transporters.•Acetate concentration can use to indicate the trend of ARO terms abundance.•Most of the influenced AROs were induced by Ruminiclostridium.•Gene numbers of cell growth and ATP generation were enhanced by H2 addition.