Use of PCR-DGGE based molecular methods to assessment of microbial diversity during anaerobic treatment of antibiotic combinations Sevcan Aydin a,⇑ , Aiyoub Shahi a , E. Gozde Ozbayram a , Bahar Ince b , Orhan Ince a a Environmental Engineering Department, Istanbul Technical University, Maslak, Istanbul, Turkey b Institutes of Environmental Sciences, Bogazici University, Bebek, Istanbul, Turkey highlights  PCR-DGGE analysis is a suitable control approach of anaerobic treatment system.  Antibiotic combinations have the most dramatic effect on acetoclastic methanogens.  Gram-negative bacteria are essential for efficient operation of anaerobic process. graphical abstract article info Article history: Received 24 March 2015 Received in revised form 22 May 2015 Accepted 24 May 2015 Available online 9 June 2015 Keywords: Anaerobic process Antibiotic combination Microbial community DGGE Cloning abstract As it is currently often not know how anaerobic bioreactors, e.g. for biogas production, react if the substrate is contaminated by toxic compounds like antibiotics. This study evaluated how anaerobic sequencing batch reactors were affected by amendments of different antibiotics and stepwise increasing concentrations. The compositions of microbial community were determined in the seed sludge using 16S rRNA gene clone libraries and PCR-DGGE analyses were used for the detection of microbial community changes upon antibiotics additions. According to PCR-DGGE results, the syntrophic interaction of acetogens and methanogens is critical to the performance of the reactors. Failure to maintain the stability of these microorganisms resulted in a decrease in the performance and stability of the anaerobic reactors. Assessment of DGGE data is also useful for suggesting the potential to control ultimate microbial community structure, especially derived from Gram-negative bacteria, through bioaugmentation to successful for antibiotic biodegradation. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Antibiotics have proven to be very effective in the treatment and prevention of microbial infections and, as such, they are com- monly prescribed in both human and veterinary medicine. This, combined with the increasing worldwide population and the utilization of antibiotics to improve the growth of livestock, has led to a significant increase in the global use and production of antibiotics. However, this has serious implications for the environ- ment (Johnson et al., 2015). After use, the human body cannot metabolize the active compounds that are present in antibiotics and, as such, they enter the environment via sewage (Tao et al., 2014). Wastewater treatment systems are incapable of removing the compounds from wastewater and the antibiotics, therefore, pollute the environment. The extent to which they can impact the microbial community that is present in the environment has http://dx.doi.org/10.1016/j.biortech.2015.05.086 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Istanbul Technical University, Civil Engineering Faculty, Environmental Engineering Department, Maslak, Istanbul, Turkey. E-mail addresses: seaydin@itu.edu.tr, sevcan_aydn@hotmail.com (S. Aydin). Bioresource Technology 192 (2015) 735–740 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech