Antibiotic ciprofloxacin is ubiquitous in the environment. However, little is known about ciprofloxacin dissipation by microbial community. The present study investigated the biodegradation potential of ciprofloxacin by mixed culture and the influential factors and depicted the structure of ciprofloxacin-degrading microbial community. Both the original microbiota from drinking water biofilter and the microbiota previously acclimated to high levels of ciprofloxacin could utilize ciprofloxacin as sole carbon and nitrogen sources, while the acclimated microbiota had a much stronger removal capacity. Temperature rise and the presence of carbon or nitrogen sources favored ciprofloxacin biodegradation. Many novel biotransformation products were identified, and four different metabolic pathways for ciprofloxacin were proposed. Bacterial community structure illustrated a profound shift with ciprofloxacin biodegradation. The ciprofloxacin-degrading bacterial community was mainly composed of classes Gammaproteobacteria, Bacteroidia, and Betaproteobacteria. Microorganisms from genera Pseudoxanthomonas, Stenotrophomonas, Phenylobacterium, and Leucobacter might have links with the dissipation of ciprofloxacin. This work can provide some new insights towards ciprofloxacin biodegradation.

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Sulfonamide antibiotics are commonly detected in the environment. Microbial degradation can play an important role in the dissipation of sulfonamide antibiotics. However, many aspects regarding the influential factor and biodegradation pathway remain essentially unclear. Moreover, phylogenetic information on the sulfonamide-degrading microbial community is still very limited. The present study investigated the biodegradation of sulfonamide antibiotic sulfanilamide by acclimated mixed culture and its influential factors, and the sulfanilamide-degrading microbial community. At the initial sulfanilamide concentration of 100 μg/L, nearly half of the antibiotic could be removed by acclimated microbial populations after 1 week of incubation, and an average removal rate of 78.3 % could be achieved in 4 weeks. p-Phenylenediamine, benzene sulfonamide, and hydroxylamine benzene sulfonamide were identified as the potential intermediates. Sulfanilamide biodegradation could be enhanced by a temperature rise and the presence of external carbon or nitrogen sources. The richness, diversity, and structure of the bacterial community showed a remarkable change with sulfanilamide biodegradation. Firmicutes and Bacteroidetes (mainly represented by classes Bacilli and Flavobacteriia) dominated the sulfanilamide-degrading bacterial community.

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