Abstract
Extremophiles are microorganisms that populate habitats considered inhospitable from an anthropocentric point of view and are able to tolerate harsh conditions such as high temperatures, extreme pHs, high concentrations of salts, toxic organic substances, and/or heavy metals. These microorganisms have been broadly studied in the last 30 years and represent precious sources of biomolecules and bioprocesses for many biotechnological applications; in this context, scientific efforts have been focused on the employment of extremophilic microbes and their metabolic pathways to develop biomonitoring and bioremediation strategies to face environmental pollution, as well as to improve biorefineries for the conversion of biomasses into various chemical compounds. This review gives an overview on the peculiar metabolic features of certain extremophilic microorganisms, with a main focus on thermophiles, which make them attractive for biotechnological applications in the field of environmental remediation; moreover, it sheds light on updated genetic systems (also those based on the CRISPR-Cas tool), which expand the potentialities of these microorganisms to be genetically manipulated for various biotechnological purposes.
Highlights
Extremophiles are microorganisms that can live in these kinds of natural niches, and based on the conditions in which they thrive, they can be grouped in: acidophiles/alkaliphiles that grow at acid or alkaline pHs, halophiles that can live at high salt concentrations, piezophiles that prosper in high pressure conditions, metallophiles that are able to thrive in presence of metals/heavy metals, psychrophiles which live at low temperatures, and thermophiles/hyperthermophiles that grow at elevated temperatures [2]
The microbial pathways that can be exploited to remove toxic metals from an environment are those related to biosorption/bioaccumulation; they consist into the ability of microorganisms to sequester heavy metals on the cell surface or intracellularly
The organic pollutants are a very heterogeneous group: the main constituents of the persistent organic pollutants (POPs) are organochlorinated pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCB), dioxins, and dibenzofurans; they are persistent because they remain intact in the environment for extended periods [77,78]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. This review analyses the metabolic strategies adopted by extremophilic microorganisms, with major emphasis on thermophilic ones, to face three classes of compounds with high impact on environmental pollution: heavy metals, organic compounds, and lignocellulosic biomasses, as well as their exploitation for application in bioremediation, biosensing, and biorefinery. It provides updates regarding available genetic systems to engineer these microorganisms, in order to use them as platforms for metabolic engineering and production of valuable compounds
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