Impact of oxytetracycline exposure on the digestive system microbiota of Daphnia magna

Antibiotics are used to treat serious illness, but may also be used extraneously or as a preventative measure in many farm animals. This usage increases the potential for unintentional exposure to a variety of organisms. When antibiotics enter aquatic environments, Daphnia magna are especially vulnerable as they filter-feed in freshwater environments. Oxytetracycline (OTC) is a commonly-used broad-spectrum antibiotic used to treat a variety of mammalian diseases. In this study, the impact of OTC on D. magna mortality and gut biota were studied using both cultivation and sequencing-based approaches. Mortality rates were extremely low with the LD50 >2,000ppm. However, OTC impacted abundance and species diversity of intestinal microorganisms in the gut of the D. magna in abundance as well as species diversity. In control organisms, Pseudomonas putida and Aeromonas hydrophila were both present while only P. putida was found in OTC-exposed organisms. Disruption of the intestinal biota in D. magna could have implications on long-term survival, energy expenditure, and reproduction.