Toxic effects of norfloxacin in soil on fed and unfed Folsomia candida (Isotomidae: Collembola) and on gut and soil microbiota.

Soils contaminated with antibiotics may exert effects on soil-dwelling animals. A systematic ecological toxicity assessment of norfloxacin on the soil collembolan Folsomia candida (F. candida) was therefore conducted in soil and Petri dish systems with and without feeding at the population, individual and cellular levels. The indicators survival, reproduction, antioxidant enzyme activities peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD), malondialdehyde (MDA) contents and gut microbiota were studied. The surrounding soil microbiota were also investigated because F. candida can ingest soil microbiota that may have effects on the gut microbiota. In general, the toxicity of norfloxacin to F. candida in contaminated soil without food addition was higher than in contaminated soil with food addition. Norfloxacin had little effect at population and individual levels but antioxidant enzyme activities changed significantly in treatments with longer exposure times or higher norfloxacin concentrations. CAT was more sensitive than SOD or POD. The diversity indices and composition at phylum level of the gut microbiota showed little change. However, the operational taxonomic units in the gut decreased in the presence of norfloxacin. The relative abundance of Wolbachia, the predominant bacterial genus in the gut, decreased significantly with increasing soil norfloxacin concentration. Wolbachia may therefore be a promising bioindicator in the assessment of norfloxacin pollution of soils at environmental concentrations.