Grasping the constraints of pure bacterial strains for the complete catabolism of micropollutants: a proteomic and kinetic study

Abstract

Research into the microbial degradation of organic micropollutants (OMP) often involves monitoring depletion of the parent compound and analyzing the biotransformation pathways that can lead to the production of metabolites, some being toxic, and/or to their mineralization. For the antibiotic sulfamethoxazole (SMX), previous studies testing a range of SMX concentration (mg down to ng L-1), have shown incomplete biotransformation of the parent SMX. This occurred both during wastewater treatment with mixed microbial communities and in studies with pure bacterial strains acclimated to SMX. This study explores the mechanism of SMX biotransformation and relationships with the proteome profile as possible reasons for the incomplete degradation of the parent SMX. Microbacterium sp BR1 served as an acclimated bacterial degrader of SMX in the range of {micro}g L-1 to ng L-1. Depletion of the SMX was incomplete whereas the metabolite 3-amino-5-methylisoxazole (3A5MI) accumulated. The activity of the enzymes for the initial transformation of the parent SMX (SadA) was higher than that of further biotransformation steps (SadB). These results showcase that even a highly sensitive and metabolically active strain at very low SMX concentrations may require complementary enzymatic machineries to degrade metabolites that have an inhibitory impact in the biodegradation and persistence of this antibiotic. SynopsisA complete removal of organic micropollutants from water is challenging. This article delves into the bacterial degradation of the antibiotic SMX and proteome analysis to clarify underlying causes of its incomplete elimination