Reversibility of enzymatic reactions might limit biotransformation of organic micropollutants

This is the accepted manuscript version of the published article: Gonzalez-Gil, L., Carballa, M., Corvini, P., & Lema, J. (2019). Reversibility of enzymatic reactions might limit biotransformation of organic micropollutants. Science Of The Total Environment, 665, 574-578. doi: 10.1016/j.scitotenv.2019.02.143Biotransformation of many organic micropollutants (OMPs) in sewage treatment plants is incomplete leading to their release into the environment. Recent findings suggest that thermodynamic aspects of the reaction as chemical equilibrium limit biotransformation, while kinetic parameters have a lower influence. Reversibility of enzymatic reactions might result in a chemical equilibrium between the OMP and the transformation product, thus impeding a total removal of the compound. To the best of our knowledge, no study has focused on proving the reversible action of enzymes towards OMPs so far. Therefore, we aimed at demonstrating this hypothesis through in vitro assays with bisphenol A (BPA) in the presence of kinase enzymes, namely acetate kinase and hexokinase, which are key enzymes in anaerobic processes. Results suggest that BPA is phosphorylated by acetate kinase and hexokinase in the presence of ATP (adenosine 5-triphosphate), but when the concentration of this co-substrate decreases and the enzymes loss their activity, the backward reaction occurs, revealing a reversible biotransformation mechanism. This information is particularly relevant to address new removal strategies, which up to now were mainly focused on modifying the kinetic parameters of the reactionThis research was funded by the Spanish Government (AEI) through COMETT project (CTQ2016-80847-R) and by FPU program with a contract (FPU13/01255) and a short research stay grant (EST16/00138). Authors from Universidade de Santiago de Compostela belong to CRETUS Strategic Partnership (AGRUP2015/02) and to Galicia Competitive Research Group (GRC ED431C 2017/29) which are co-funded by FEDER (EU)S

Biodegradation of sulfamethoxazole and other sulfonamides by Achromobacter denitrificans PR1

This study aimed to isolate and characterize a microbial culture able to degrade sulfonamides. Sul-famethoxazole (SMX)-degrading microorganisms were enriched from activated sludge and wastewater.The resultant mixed culture was composed of four bacterial strains, out of which only Achromobacterdenitrificans PR1 could degrade SMX. This sulfonamide was used as sole source of carbon, nitrogen andenergy with stoichiometric accumulation of 3-amino-5-methylisoxazole. Strain PR1 was able to removeSMX at a rate of 73.6 ± 9.6 molSMX/gcell dry weighth. This rate more than doubled when a supplement ofamino acids or the other members of the mixed culture were added. Besides SMX, strain PR1 was able todegrade other sulfonamides with anti-microbial activity. Other environmental Achromobacter spp. couldnot degrade SMX, suggesting that this property is not broadly distributed in members of this genus.Further studies are needed to shed additional light on the genetics and enzymology of this process.info:eu-repo/semantics/publishedVersio

Biotransformation of Sulfonamide Antibiotics in Activated Sludge: The Formation of Pterin-Conjugates Leads to Sustained Risk

The presence of antibiotics in treated wastewater and consequently in surface and groundwater resources raises concerns about the formation and spread of antibiotic resistance. Improving the removal of antibiotics during wastewater treatment therefore is a prime objective of environmental engineering. Here we obtained a detailed picture of the fate of sulfonamide antibiotics during activated sludge treatment using a combination of analytical methods. We show that pterin-sulfonamide conjugates, which are formed when sulfonamides interact with their target enzyme to inhibit folic acid synthesis, represent a major biotransformation route for sulfonamides in laboratory batch experiments with activated sludge. The same major conjugates were also present in the effluents of nine Swiss wastewater treatment plants. The demonstration of this biotransformation route, which is related to bacterial growth, helps explain seemingly contradictory views on optimal conditions for sulfonamide removal. More importantly, since pterin-sulfonamide conjugates show retained antibiotic activity, our findings suggest that risk from exposure to sulfonamide antibiotics may be less reduced during wastewater treatment than previously assumed. Our results thus further emphasize the inadequacy of focusing on parent compound removal and the importance of investigating biotransformation pathways and removal of bioactivity to properly assess contaminant removal in both engineered and natural systems