Microplastics, horizontal gene transfer, and impacts on human health

Horizontal gene transfer
Horizontal gene transfer

An estimated 300 million tons of plastics are produced annually. Millions of those tons enter our air, soil, and water as waste every year. As waste, some of this material–still millions of tons–breaks down into smaller particles, or microplastics (< 5 mm in size); the microplastics come from the manufacture of industrial products and the physical, chemical, and biological degradation of larger pieces of plastic waste. “In urban areas, waste-water treatment plants constitute … important sources of microplastics, releasing up to several million pieces per day.”

Microplastics constitute pollutants that decompose extremely slowly and “act as long-lasting reactive surfaces, containing additives and/or absorbing organic matter and chemical substances, such as heavy metals, antibiotics, pesticides, and other xenobiotics. Additionally, microplastics can be colonized by different microbial communities from natural surface-attached and free-living microbial communities.”

A feature of microplastics “is their potential as so-called ‘hot-spots’ of horizontal gene transfer (HGT), as they display areas of increased nutrient availability and high cell densities of microbial cells, allowing for intense interactions. Conjugation is the main mechanism of directed HGT, a process in which two bacteria in close contact can exchange genetic information via plasmid transfer from a donor to a recipient cell. This process can occur even between distantly related taxa, affecting bacterial evolution and the spread of multiple phenotypic traits, such as antibiotic or heavy metal resistance genes.”

Microplastics “provide new hot spots for spreading antibiotic resistance genes … in natural aquatic ecosystems. Tons of microplastics in sites like wastewater treatment plants that get colonized by a multitude of microorganisms including pathogenic bacteria from humans or animals pose a tremendous potential for antibiotic resistance spreading by HGT. Effluents of wastewater treatment plants often flow into natural aquatic ecosystems, where some of the original pathogenic species may persist in the floating biofilm. During the transit through these aquatic ecosystems, processes of horizontal and vertical gene transfer on the associated bacteria can occur continuously. Multiple encounters between the microplastics-associated bacterial community and various natural populations are likely given that plastic particles remain present in the environment for extremely long periods, resulting even in their transfer to the gut microbiota of organisms feeding on microplastics.”

“Microplastics provide favorable conditions for the establishment of groups of microorganisms that differ from those in the surrounding water or on natural aggregates, thereby altering the structure and composition of microbial communities in aquatic environments. On plastics, an increased permissiveness towards plasmids carrying antibiotic resistance genes and eventually other genes facilitates the establishment of novel traits in bacterial communities by evolutionary changes at the species and population levels. Microplastics provide ideal conditions for collection, transport and dispersion of microorganisms and their associated mobile genetic elements over long distances, which could even reach a global scale. This poses increasing but greatly neglected hazards to human health because pathogens can invade new localities and natural, non-pathogenic microorganisms can potentially acquire and thus rapidly spread antibiotic resistance.”

Featured article:

Arias-Andres, M., Klümper, U., Rojas-Jimenez, K., & Hans-Peter Grossart. (2018). Microplastic pollution increases gene exchange in aquatic ecosystems. Environmental Pollution, 237, 253-261. [PDF] [Cited by]

For additional research, please see the Science Primary Literature Database.

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