Microbial community dynamics during anaerobic digestion of OTC medicated cow manure using DDGE and clone libraries

Abstract

Veterinary antibiotics used in cattle medication may have inhibitory effects on microorganisms in anaerobic digestion of manure for biogas production as a renewable energy. Since microbial community plays an important role in digestion process, defining effects of antibiotics on microbial diversity can lead to improvements in understanding of interactions and processes, thereby obtaining better performance in terms of higher digestion capacity and biogas production. In this study, effect of OTC as a common veterinary antibiotic on biogas production and microbial communities was investigated with two microcosm tests: in the first part, OTC was externally added to manure slurries and in the second part, as in practical applications, a cow was medicated with OTC and manure samples of medicated cow was used as substrate in the microcosms. In the first part, 90±2 L/kgTVS methane yield was observed after 30 days in control microcosms. Inhibitions in biogas productions were 41%, 57% and 61% in the 50 mg/L, 100 mg/L and 200 mg/L OTC added digesters, respectively. For 50 mg/L OTC added microcosms, retardation in the biogas production was observed and almost the same amount of biogas with control was produced after 60 days. Bacterial community similarities of OTC added microcosms to control were lower (64-92%) than archaeal community similarities (94-99%). In the second part, methane yield of the control microcosms were 87±6 L/kgTVS. In medicated manure collected on day 1, 10 mg/kg OTC was measured, and the concentrations decreased to undetectable limit after 12 days. Biogas inhibitions in the manures collected on the first 5 days were between 50-60% whereas that of was 23% for day 10. Samples collected on day 15 and 20 produced similar amount of biogas with the control. Archaeal community similarities of manures collected on first 10 days to control were lower (73-93%) than bacterial community similarities (93-98%). Mostly related species with biogas production was found as Methanobacteriales spp. in a syntrophic relation with Clostridium spp. Almost all bacterial and archaeal species were negatively affected by OTC.