Isolation, Identification and Genomic Characterization of Carbamazepine-Tolerant Bacteria from Contaminated Aquatic...

Pharmaceutical contamination in aquatic environments has increased interest in microorganisms able to tolerating these compounds and the mechanisms underlying their tolerance. This study isolated and characterized carbamazepine (CBZ)-tolerant bacteria from contaminated waters of the Machángara River, Quito, Ecuador, and investigated the genome of the most tolerant isolate. Isolates were characterized by morphological and biochemical analyses, and 16S rRNA gene sequencing. Tolerance to CBZ (1-50 mg L^-1) was evaluated by culture-based growth measurements. CBZ1, CBZ3, CBZ6, and CBZ7 were taxonomically assigned to Enterobacter hormaechei, Paenibacillus lactis, Aeromonas hydrophila and Raoultella ornithinolytica, respectively. Among the four isolates evaluated, CBZ7 exhibited significantly higher relative growth at elevated CBZ concentrations (30-50 mg L^-1) and was therefore selected for whole-genome sequencing. The CBZ7 draft genome comprised 5,671,759 bp distributed across 181 contigs, with a G+C content of 55.65%, an N50 of 79,780 bp, 98.2% BUSCO completeness, and CheckM2 estimates 0.87% contamination. Genome annotation revealed genes associated with membrane transport and efflux, oxidative metabolism, glutathione metabolism, environmental sensing, and aromatic compound metabolism. Although no complete CBZ-specific catabolic pathway was identified, the results support strong tolerance of CBZ7 to elevated CBZ concentrations and identity candidate functions potentially involved in xenobiotic adaptation.