**Chu-Wen Yang, Chien Liu and Bea-Ven Chang \***

Department of Microbiology, Soochow University, Taipei 11101, Taiwan; ycw6861@scu.edu.tw (C.-W.Y.); jennifer719123@yahoo.com.tw (C.L.)

**\*** Correspondence: bvchang@scu.edu.tw; Tel.: +886-228-819-471 (ext. 6859)

Received: 22 May 2020; Accepted: 28 July 2020; Published: 30 July 2020

**Abstract:** The removal of antibiotics from the aquatic environment has received great interest. The aim of this study is to examine degradation of oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC), amoxicillin (AMO), sulfamethazine (SMZ), sulfamethoxazole (SMX), sulfadimethoxine (SDM) in sludge. Four antibiotic-degrading bacterial strains, SF1 (*Pseudmonas* sp.), A12 (*Pseudmonas* sp.), strains B (*Bacillus* sp.), and SANA (*Clostridium* sp.), were isolated, identified and tested under aerobic and anaerobic conditions in this study. Batch experiments indicated that the addition of SF1 and A12 under aerobic conditions and the addition of B and SANA under anaerobic conditions increased the biodegradation of antibiotics in sludge. Moreover, the results of repeated addition experiments indicated that the efficiency of the biodegradation of antibiotics using the isolated bacterial strains could be maintained for three degradation cycles. Two groups of potential microbial communities associated with the aerobic and anaerobic degradation of SMX, AMO and CTC in sludge were revealed. Twenty-four reported antibiotics-degrading bacterial genera (*Achromobacter*, *Acidovorax*, *Acinetobacter*, *Alcaligenes*, *Bacillus*, *Burkholderia*, *Castellaniella*, *Comamonas*, *Corynebacterium*, *Cupriavidus*, *Dechloromonas*, *Geobacter*, *Gordonia*, *Klebsiella*, *Mycobacterium*, *Novosphingobium*, *Pandoraea*, *Pseudomonas*, *Rhodococcus*, *Sphingomonas*, *Thauera*, *Treponema*, *Vibrio* and *Xanthobacter*) were found in both the aerobic and anaerobic groups, suggesting that these 24 bacterial genera may be the major antibiotic-degrading bacteria in sludge.

**Keywords:** sludge; antibiotics; biodegradation
