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.
Highlights
This review summarizes the different organic micropollutants (OMPs)-transforming genes located on mobile genetic elements (MGEs) in wastewater treatment plants (WWTPs) and the tools for analyzing MGEs in complex environmental samples
Microorganisms have been in contact with OMPs for a relatively short period on an evolutionary time scale, so the metabolic pathways are still being developed
OMP degradation genes are often linked to MGEs
Summary
The stable integration of these genes in the chromosome will occur if OMPs become the main energy and carbon sources for some bacteria in environments with a constant and high OMP concentration (Tazzyman and Bonhoeffer, 2014) This is not the current situation in WWTPs, so MGEs still play a crucial role in OMP biodegradation. MGEs accelerate microbial adaptation to the transformation of new chemicals (Top and Springael, 2003), so they might be actively involved in OMP removal in WWTPs. Several studies have found similar catabolic gene clusters in phylogenetically unrelated strains isolated from geographically distant soils and WWTPs (van der Meer et al, 1992; Williams and Sayers, 1994; Ouchiyama et al, 1998; Shintani et al, 2005). Studies linking MGE abundance to pesticide turnover in agricultural WWTPs will be examined, and gaps in the knowledge of the contribution of catabolic MGEs to wastewater treatment will be highlighted
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