The role of mobile genetic elements in organic micropollutant degradation during biological wastewater treatment

Abstract

Wastewater treatment plants (WWTPs) are crucial for producing clean effluents from polluting sources such as hospitals, industries, and municipalities. In recent decades, many new organic compounds have ended up in surface waters in concentrations that, while very low, cause (chronic) toxicity to countless organisms. These organic micropollutants (OMPs) are usually quite recalcitrant and not sufficiently removed during wastewater treatment. Microbial degradation plays a pivotal role in OMP conversion. Microorganisms can adapt their metabolism to the use of novel molecules via mutations and rearrangements of existing genes in new clusters. Many catabolic genes have been found adjacent to mobile genetic elements (MGEs), which provide a stable scaffold to host new catabolic pathways and spread these genes in the microbial community. These mobile systems could be engineered to enhance OMP degradation in WWTPs, and this review aims to summarize and better understand the role that MGEs might play in the degradation and wastewater treatment process. Available data about the presence of catabolic MGEs in WWTPs are reviewed, and current methods used to identify and measure MGEs in environmental samples are critically evaluated. Finally, examples of how these MGEs could be used to improve micropollutant degradation in WWTPs are outlined. In the near future, advances in the use of MGEs will hopefully enable us to apply selective augmentation strategies to improve OMP conversion in WWTPs.

Effect of concentration and hydraulic reaction time on the removal of pharmaceutical compounds in a membrane bioreactor inoculated with activated sludge

“…The biomass density in the bioreactor presented in this study was ten times lower than a common WWTP activated sludge reactor. As conjugation events are more likely to happen at higher densities or in environments where cells are in close contact such as granules and biofilms (Rios‐Miguel et al ., 2020), this experiment might underestimate the true role that MGEs play in the degradation of pharmaceutical micropollutants. Furthermore, previous studies reported higher relative abundances of MGEs in sites with higher OMP exposure over much longer periods of time (years) compared with our bioreactor experiment that lasted 2.5 months (Dunon et al ., 2013; Dealtry et al ., 2014).…”

“…Mobile genetic elements (MGEs) have been previously suggested to be involved in microbial adaptation. MGEs may thus play a role in the biodegradation of xenobiotics or organic micropollutants in different environments such as soils and WWTPs (Top and Springael, 2003; Rios‐Miguel et al ., 2020). Furthermore, previous studies found a correlation between pesticide exposure and MGE abundance in soils and agricultural WWTPs (Dunon et al ., 2013; Dealtry et al ., 2014).…”

Microbial paracetamol degradation involves a high diversity of novel amidase enzyme candidates

“…Our strain, Pfast, also had two insertion sequences (IS6100 and IS21, OACKLNDA_05756, OACKLNDA_05781), one Tn3 transposase gene (OACKLNDA_05752), and one recombinase gene (OACKLNDA_05755) near the highly-expressed amidase gene. Consequently, the whole gene cluster might have been exchanged between different species via horizontal gene transfer (HGT) (Rios Miguel et al, 2020). Finally, the low number of homologous proteins in the NCBI database might indicate the recent evolution of this amidase towards paracetamol biodegradation or our limited ability to find and identify these genes.…”

Effect of concentration and hydraulic reaction time on the removal of pharmaceutical compounds in a membrane bioreactor inoculated with activated sludge

“…The biomass density in the bioreactor presented in this study was ten times lower than a common WWTP activated sludge reactor. As conjugation events are more likely to happen at higher densities or in environments where cells are in close contact such as granules and biofilms (Rios-Miguel et al, 2020), this experiment might underestimate the true role that MGEs play in the degradation of pharmaceutical micropollutants. Furthermore, previous studies reported higher relative abundances of MGEs in sites with higher OMP exposure over much longer periods of time (years) compared to our bioreactor experiment that lasted 2.5 months (Dealtry et al, 2014;Dunon et al, 2013).…”

“…Mobile genetic elements (MGEs) have been previously suggested to be involved in microbial adaptation. MGEs may thus have played a role in the biodegradation of xenobiotics or organic micropollutants in different environments such as soils and WWTPs (Rios-Miguel et al, 2020;Top and Springael, 2003). Furthermore, previous studies found a correlation between pesticide exposure and MGE abundance in soils and agricultural WWTPs (Dealtry et al, 2014;Dunon et al, 2013).…”