S98: Investigation of bacterial tetracycline degradation pathways

Environmental contamination with antibiotics has been a subject of concern worldwide.  The goal of this study was to understand the degradation mechanism of tetracycline (TC) in bacteria that are highly tolerant to TC (minimum inhibitory concentration > 600 ppm).  These bacteria were recovered from the rhizosphere of vetiver grass (Chrysopogon zizanioides) during hydroponic TC remediation trials in our lab and then screened to verify their use of TC as a sole carbon/energy source. HPLC and MS-MS results first showed that these bacteria transformed TC into its more persistent and harmful (carcinogenic) isomers, epi and anhydro-TC, within 7 days; these isomers were removed within about 14 days.  Comparative metabolomics studies were then conducted in several different TC-degrading bacteria grown with and without TC.  After extraction and derivitization, samples were run on GC-MS and the analyzed samples were run through MeV 2.0, Metaboloanalyst 2.0 and KEGG for pathway analysis.  Intracellular metabolomics results indicated that six compounds were up-regulated in the TC cultures vs. controls.  Several metabolites with significant differences (p<0.05) related to TC degradation pathways were palmitic and stearic acids, which are a part of fatty acid metabolism. Extracellular metabolomics results are currently being analyzed to identify and confirm the TC degradation pathway used by these bacteria.  Understanding the antibiotic degradation pathway will help in the implementation of a targeted biological remediation system for contaminated water sources.