Abstract: An anaerobic digestion chemostat using butyrate as the sole carbon source was constructed in this study. 16S rRNA high-throughput sequencing was employed to investigate the dynamic changes of butyrate-degrading microbial community under inhibition of chlortetracycline（CTC）and co-effects of CTC and granular active carbon（GAC）,and to explore the interactions among microorganisms under environmental stress and their responses to sole CTC inhibition and co-effects of CTC and GAC. Our results showed that known syntrophic butyrate degrading bacterium Syntrophomonas（11.6%）and the aceticlastic methanogen Methanosaeta（48.5%）respectively dominated the bacterial and archaeal community in the original chemostat. Addition of 40 mg/L and 50 mg/L CTC led to the inhibitory effects on methane production reduction by 40.4% and 49.3%,respectively. Although Syntrophomonas presented tolerance to CTC,bacteria（e.g.,unclassified Firmicutes and unclassified Comamonadaceae）having positive correlations with it and known acetate-oxidizing bacteria Tepidanaerobacter were significantly inhibited by CTC,which thus affected the degradation of butyrate and caused the accumulation of metabolites,further resulting in the reduction of methane. Methane production reduced by 2.9%,48.5%,and 64.7% when adding GAC along,as well as adding GAC under the 40 mg/L and 50 mg/L CTC,respectively. Co-occurrence network analysis revealed that the addition of GAC significantly enhanced the activity of Geobacter and bacterium that showed positive correlation with it（e.g.,Azonexus）. However,Methanosaeta and Methanoculleus showed significantly negative correlation with most of the bacteria（e.g.,Azonexus）. Thus,the addition of GAC may indirectly affect the activity of Methanosaeta and Methanoculleus.

Key words: anaerobic digestion, syntrophic butyrate oxidation, antibiotics, granular activated carbon, interspecies direct electron transfer