ENVIRONMENTAL BIOTECHNOLOGY Changes in microbial community structures due to varying operational conditions in the anaerobic digestion of oxytetracycline-medicated cow manure Gokhan Turker 2 & Sevcan Aydin 1 & Çağrı Akyol 2 & Orhan Yenigun 2 & Orhan Ince 1 & Bahar Ince 2 Received: 6 February 2016 /Revised: 6 March 2016 /Accepted: 8 March 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract Management of manure containing veterinary anti- biotics is a major concern in anaerobic treatment systems be- cause of their possible adverse effects on microbial commu- nities. Therefore, the aim of study was to investigate how oxytetracycline (OTC) influences bacteria and acetoclastic and hydrogenotrophic methanogens under varying operation- al conditions in OTC-medicated and non-medicated anaerobic cow manure digesters. Concentrations of OTC and its metab- olites throughout the anaerobic digestion were determined using ultraviolet-high-performance liquid chromatography (UV-HPLC) and tandem liquid chromatography-mass spec- trometry (LC/MS/MS), respectively. Fluorescent in situ hy- bridization, denaturing gradient gel electrophoresis, cloning, and sequencing analyses were used to monitor changes in microbial community structures. According to the results of analytical and molecular approaches, operating conditions highly influence active microbial community dynamics and associate with biogas production and elimination of OTC and its metabolites during anaerobic digestion of cow manure in the presence of an average initial concentration of 2.2 mg OTC/L. The impact of operating conditions has a drastic effect on acetoclastic methanogens than hydrogenotrophic methanogens and bacteria. Keywords Anaerobic digestion . Cow manure . Oxytetracycline . Biogas . Microbial community Introduction Animal manure has a great potential with respect to organic matter (COD equivalent of 90,000 mg O 2 /L). In this regard, livestock industry, which produces a large amount of manure requiring treatment and stabilization, can benefit from anaer- obic digestion (AD) (Massé and Saady 2015). Anaerobic bio- degradation uses this potential to produce methane through several biochemical processes where many different species of anaerobic bacteria and archaea involved (Arikan 2008; Álvarez et al. 2010). Therefore, the system itself is delicate and susceptible to inhibitors, which may hinder performance of the process (Lallai et al. 2002; Aydin et al. 2015a; Lins et al. 2015). Antibiotics in manure cause a problem because of the loss of energy recovery not only in digesters but also in soil when they are applied as fertilizers. In recent years, there are many studies published in subject of detection of various an- tibiotics in soil (Mata-Alvarez et al. 2011) and the main source of antibiotics in the environment is reported to be wastewater discharge, manure disposal, and aquaculture (Ding and He 2010). Antibiotics are recalcitrant compounds, and they are highly susceptible for accumulation (Kemper 2008; Jechalke et al. 2014). The presence of antibiotics in manure also causes another problem, which may also become a public health is- sue. Low amounts of antibiotics present in manure and fertil- ized soil may also trigger occurrence of metabolites (Yuan et al. 2010; McKinney et al. 2010; Rizzo et al. 2013). Bacteria may gain resistance over time, and this gene can also be transferred in the ecosystem where it may end up as a major outbreak of resistance pathogens in a town or hospital (Zhu et al. 2013; Joy et al. 2014; Aydin et al. 2015a). Electronic supplementary material The online version of this article (doi:10.1007/s00253-016-7469-9) contains supplementary material, which is available to authorized users. * Sevcan Aydin sevcan_aydn@hotmail.com 1 Department of Environmental Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey 2 Institute of Environmental Sciences, Boğaziçi University, Bebek, 34342 Istanbul, Turkey Appl Microbiol Biotechnol DOI 10.1007/s00253-016-7469-9