Antibiotics are frequently used in the United States as feed efficiency promoters and medicines for livestock that is destined for human consumption. These antibiotics are released into the environment through the runoff and wastewater streams from animal feedlots and land applications of manure. The exposure of microorganisms to these antibiotics has reportedly resulted in the development of resistant species of microorganisms, which in turn can lead to human health hazards. Phytoremediation of these antibiotics can be a useful tool for countering this problem. Aquatic plants, Myriophyllum aquaticum (parrot feather) and Pistia stratiotes (water lettuce), were used for studying phytoremediation of tetracycline (TC) and oxytetracycline (OTC) from aqueous media. TC and OTC are two of the most commonly used tetracyclines in veterinary medicine. M. aquaticum and P. stratiotes gave high antibiotic modification rates of both antibiotics. Kinetic analyses dismiss direct enzyme catalysis; the modification rates decreased with increasing OTC concentrations. Sterile, cell-free root exudates (filtered through 0.2 microm membranes) from both species also exhibited comparable antibiotic modification rates. The involvement of root-secreted metabolites in antibiotic modification is suggested. The changes in the UV absorbance spectra of OTC during treatment with the root exudates confirmed the modification.

The release of antibiotics to the environment has to be controlled because of serious threats to human health. Hairy root cultures of Helianthus annuus (sunflower), along with their inherent rhizospheric activity, provide a fast growing, microbe-free environment for understanding plant-pollutant interactions. The root system catalyzes rapid disappearance of tetracycline (TC) and oxytetracycline (OTC) from aqueous media, which suggests roots have potential for phytoremediation of the two antibiotics in vivo. In addition, in vitro modifications of the two antibiotics by filtered, cell- and microbe-free root exudates suggest involvement of root-secreted compounds. The modification is confirmed from changes observed in UV spectra of exudate-treated OTC. Modification appears to be more dominant at the BCD chromophore of the antibiotic molecule. Kinetic analyses dismiss direct enzyme catalysis; the modification rates decrease with increasing OTC concentrations. The rates increase with increasing age of cultures from which root exudates are prepared. The decrease in modification rates upon addition of the antioxidant ascorbic acid (AA) suggests involvement of reactive oxygen species (ROS) in the antibiotic modification process.