Biodegradation of the Antibiotic Doxycycline by Bacteria from the Gastrointestinal Tract of Cucurbit Beetles (Diabrotica speciosa)

Antibiotics can contaminate the environment as a result of improper disposal. The induction of doxycycline in the environment could give rise to lineages of the cucurbit beetle Diabrotica speciosa containing resistant endosymbiotic microorganisms, giving rise to bacterial strains capable of biodegrading these antibiotic residues. This work determined the relationship between the intestinal microbiota of D. speciosa and its ability to biodegrade an antibiotic. Bacterial strains of Enterobacter cloacae and Stenotrophomonas maltophila isolated from the gastrointestinal tract of D. speciosa were evaluated for the biodegradation of doxycycline. An analytical method for the extraction and quantification of doxycycline by high-efficiency liquid chromatography-ultraviolet detection (HPLC-UV) was developed and applied to monitor the biodegradation rates during bacterial growth for nutrient and nutrient-deficient media, both supplemented with the antibiotic. Degradation kinetics showed a decrease in antibiotic concentration after 96 h in saline medium, with recoveries of 63.1 and 87.7% for E. cloacae and S. maltophilia, respectively. Two degradation products were then identified and characterized from the liquid chromatography-high resolution mass spectrometry data after bioassays with E. cloacae. The gastrointestinal tract of insects such as D. speciosa can be a source of useful microbes for biotechnological processes such as the biodegradation of exogenous organic compounds in the environment.