Abstract
Dioxins are the most toxic known environmental pollutants and are mainly formed by human activities. Due to their structural stability, dioxins persist for extended periods and can be transported over long distances from their emission sources. Thus, dioxins can be accumulated to considerable levels in both human and animal food chains. Along with sediments, soils are considered the most important reservoirs of dioxins. Soil microorganisms are therefore highly exposed to dioxins, leading to a range of biological responses that can impact the diversity, genetics and functional of such microbial communities. Dioxins are very hydrophobic with a high affinity to lipidic macromolecules in exposed organisms, including microbes. This review summarizes the genetic, molecular and biochemical impacts of dioxins on the lipid metabolism of soil microbial communities and especially examines modifications in the composition and architecture of cell membranes. This will provide a useful scientific benchmark for future attempts at soil ecological risk assessment, as well as in identifying potential dioxin-specific-responsive lipid biomarkers. Finally, potential uses of lipid-sequestering microorganisms as a part of biotechnological approaches to the bio-management of environmental contamination with dioxins are discussed.
Highlights
Dioxins, polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), are the most toxic group of persistent organic pollutants (POPs) that have been described to date (WHO 2016)
Effects of dioxins on lipid metabolism in soil microorganisms There are multiple lines of genetic, molecular and biochemical evidence demonstrating that dioxins, notably TCDD, alter lipid metabolism by affecting the activity of certain key enzymes in fatty acids (FAs) biosynthesis, levels of triacylglycerols, cholesterols and free FAs in plasma of animals, plants and humans exposed to dioxins
A similar adaptive scenario was recently reported for TCDD-exposed B. megaterium A14K that exhibited a specific lipidic “signature” due to the presence of branched-chain unsaturated fatty acids (BCUFAs) (Hanano et al 2019b). This suggests a possible activation of membrane-bound desaturases that act on existing branched-chain saturated FAs (BCSFAs) in cell membrane to produce the corresponding BCUFAs, which are tentatively considered as lipid biomarkers to dioxin exposure (Hanano et al 2019b)
Summary
Dioxins, polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), are the most toxic group of persistent organic pollutants (POPs) that have been described to date (WHO 2016). Soil microorganisms are liable to be exposed to dioxins, leading to a range of biological responses that impacts the diversity, genetics and functional of affected microbial communities (Hanano et al 2014c; Kimura and Kamagata 2009). It begins with a brief background on the nature of dioxins as lipophilic environmental contaminants and examines their impacts on microbial lipid metabolism with respect to the composition of cellular fatty acids (FAs).
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