Carbonaro, Miriam (2024) Extremophiles as microbial tools to face environmental problems associated to anthropogenic activities. [Tesi di dottorato]

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Abstract

This thesis, entitled "Extremophiles as microbial tools to face environmental problems associated with anthropogenic activities", aims to demonstrate the feasibility of sustainable solutions in biotechnology based on the use of extremophiles, with a particular focus on thermophiles and their enzymes. The study of these extraordinary microorganisms can provide new tools for many applications among which environmental issues and valorization of renewable resources. Chapter 2 offers a comprehensive overview of these microorganisms emphasizing their importance in various biotechnological fields. Their adaptability to thrive in pollutants and biomass wastes makes them ideal for environmental preservation, including heavy metal remediation and biomass valorization. The potential for engineering these microorganisms for improved performance is also discussed. Chapter 3 focuses on the identification of TtArsM, a SAM-dependent arsenite methyltransferase with a role in the arsenic resistance system of the Gram-negative bacterium Thermus thermophilus HB27. In vivo studies on enzyme function have been possible thanks to the set-up of CRISPR-Cas9 genome editing technology for T. thermophilus; the tool has also been used to develop a whole-cell arsenic bioreporter system. In the following section (Chapter 4) Alicyclobacillus mali FL18, a Gram-positive thermo-acidophilic bacterium, is examined with an emphasis on its capacity to produce lignocellulolytic enzymes. Genomic analysis reveals genes for 73 putative carbohydrate-active enzymes (CAZymes), including the multifunctional GH9 family member, AmCel9, exhibiting exceptional cellulolytic activity. In the second section of Chapter 4, the study delves into Geobacillus stearothermophilus GF16, a Gram-positive thermophilic bacterium, and the ability of its secretome to degrade lignocellulose. The bacterium, grown on minimal medium enriched with xylan, has significant xylanolytic activity. The secretome of G. stearothermophilus GF16 effectively hydrolyzes various agri-food residues, highlighting its potential for an eco-friendly lignocellulose degradation strategy. The concluding Chapter 5 focuses on three glucuronoyl esterases (GEs). These enzymes, belonging to CE15 family, have been characterised from the endophyte Dyadobacter fermentans NS114T and play a crucial role in cleaving ester bonds within lignin-carbohydrate complexes. Their diverse catalytic efficiencies and structural features have been explored, with the goal of deepening their potential for overcoming recalcitrance in lignocellulosic waste utilization.

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