Changes in microbial community structures due to varying operational conditions in the anaerobic digestion of oxytetracycline-medicated cow manure

Abstract

Management of manure containing veterinary antibiotics is a major concern in anaerobic treatment systems because of their possible adverse effects on microbial communities. Therefore, the aim of study was to investigate how oxytetracycline (OTC) influences bacteria and acetoclastic and hydrogenotrophic methanogens under varying operational conditions in OTC-medicated and non-medicated anaerobic cow manure digesters. Concentrations of OTC and its metabolites throughout the anaerobic digestion were determined using ultraviolet-high-performance liquid chromatography (UV-HPLC) and tandem liquid chromatography-mass spectrometry (LC/MS/MS), respectively. Fluorescent in situ hybridization, 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.

Antibiotic Inhibition on Anaerobic Digestion of Animal Manure and Controlling Strategies: A Short Review

“…But among the four types of anaerobic microorganisms, methanogens are the least tolerant to environmental toxicants due to their slow growth rate and are most likely to be inhibited by antibiotics . Turker et al observed temporary changes in the bacterial community structure and a decrease in the diversity during AD of oxytetracycline‐medicated cow manure. However, certain bacterial groups recovered after a short period of adaptation, suggesting that they were tolerant of oxytetracycline and the metabolites.…”

“…However, certain bacterial groups recovered after a short period of adaptation, suggesting that they were tolerant of oxytetracycline and the metabolites. Compared with the bacterial community, the effect of antibiotics on methanogenic archaea is more pronounced . According to Bauer et al, the presence of chlortetracycline (8000 mg kg −1 dry matters) did not significantly affect the 16S rRNA gene copy number of fermentative bacteria, while it dramatically reduced the 16S rRNA gene copy number of methanogens by >50%.…”

“…Methanogenesis is mediated by two groups of methanogens: 1) acetate‐utilizing acetoclastic methanogens and 2) hydrogenotrophic methanogens in syntrophic association with syntrophic acetate‐oxidizing (SAO) bacteria that convert H 2 and CO 2 into methane. Several previous studies have suggested the dominance of hydrogenotrophic methanogens over acetoclastic methanogens at high antibiotic concentrations . Aydin et al employed real‐time PCR to determine the effect of erythromycin, tetracycline, and sulfamethoxazole on methanogenic archaea, and they reported that hydrogenotrophic methanobacteriales was the key member responsible for methane production under high antibiotic stress.…”

“…By studying the structure of microbial community in different reactors, Akyol et al suggested that the bacterial diversity in acidogenic reactor and the archaeal diversity in methanogenic reactor was higher than those in single‐stage digesters during the AD period. It was suggested that adequate mixing is beneficial for oxytetracycline degradation during AD of cow manure, but an increase in mixing rate could lead to deteriorated biogas production . Optimization of the carbon to nitrogen ratio by adding lignocellulosic materials also provides a feasible solution to counteract antibiotic inhibition .…”

“…Compared with the bacterial community, the effect of antibiotics on methanogenic archaea is more pronounced. [55][56][57] According to Bauer et al, [34] the presence of chlortetracycline (8000 mg kg À1 dry matters) did not significantly affect the 16S rRNA gene copy number of fermentative bacteria, while it dramatically reduced the 16S rRNA gene copy number of methanogens by >50%. Methanogenesis is mediated by two groups of methanogens: 1) acetate-utilizing acetoclastic methanogens and 2) hydrogenotrophic methanogens in syntrophic association with syntrophic acetate-oxidizing (SAO) bacteria that convert H 2 and CO 2 into methane.…”