Microbial responses to pharmaceutical contamination in wastewater: consortia-based enrichment and isolation of ketoprofen- and oxazepam-degrading bacteria from activated sludge

The continuous discharge of pharmaceutical residues into the environment remains a critical ecological concern. Conventional WWTPs inadequately remove many recalcitrant pharmaceuticals and may alter the composition of microbial communities. This study analyzed the dynamics of microbial communities under pharmaceutical stress, and utilizing their selective pressure to isolate individual strains with biodegradation potential. The concentration of pharmaceuticals as well as microbial in situ analysis were first characterized in two WWTPs receiving urban and hospital influents. A targeted consortia-based enrichment approach was then performed using aerobic sludge from both WWTPs. Ketoprofen (KETO) and oxazepam (OXA) were selected representing relatively biodegradable and highly recalcitrant pharmaceuticals, respectively. Enrichment experiments were conducted at 1 and 1000 ppm under nutrient-rich and nutrient-limited conditions. Interestingly, microbial community composition was primarily shaped by carbon availability and suggest that pharmaceutical type and their concentration contribute to microbial community differentiation. Successive enrichments generated 18 KETO consortia, of which 11 achieved 15–74% degradation efficiency. Twenty-four strains were isolated, and eight degraded KETO by more than 25%. In contrast, OXA consortia showed almost no degradation, although four of 28 isolated strains achieved moderate degradation, suggesting previously unreported degradation potential despite partial abiotic loss. Nutrient-limited conditions and higher pharmaceutical concentrations favored the selection of strains with enhanced degradation capacities, suggesting that stronger selective pressure promotes catabolic pathways linked to degradation. These findings provide new insights into microbial adaptation to pharmaceutical contaminants while demonstrating the value of a consortia-based enrichment strategy for isolating biodegrading microorganisms.