Maresca, Emanuela (2024) STRATEGIES FOR WASTE VALORIZATIONAND VALUE-ADDED CHEMICALSPRODUCTION THROUGH MICROBIAL CELL FACTORIES. [Tesi di dottorato]

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Abstract

The thesis highlights innovative green strategies to transform waste into value-added chemicals through microbial cell factories, contributing to sustainability and efficiency within the circular economy. The first section discusses the use of Heyndrickxia coagulans (formerly Bacillus/Weizmannia coagulans), a probiotic and lactic acid-producing widely used in food and biotechnology (Manuscript I). Unlike other probiotics, H. coagulans thrives at moderately high temperatures and near-neutral pH, making it ideal for various industrial applications, including the eco-friendly production of lactic acid. The research then investigates the use of a thermophilic strain of H. coagulans MA-13 to produce lactic acid from citrus waste (Manuscript II). The study combines enzymatic pre-treatment of the waste with the fermentation capabilities of MA-13, demonstrating its effectiveness in converting agri-food residues into lactic acid under anaerobic conditions at 55°C. The results showed that the microorganism's robustness, even in the presence of antimicrobial compounds from citrus waste, makes it a promising candidate for sustainable bioprocesses. In addition to lactic acid production, the thesis explores the potential of H. coagulans MA-13 to enhance the nutritional and sensory qualities of yellow peas through solid-state fermentation (Manuscript III in preparation), offering an alternative to meat-based products. The process improved the safety and shelf-life of the fermented peas and highlighted the potential use of MA-13 in co-cultures with Tempeh (Rhizopus spp.), creating new functional foods. Another section of the study investigates the adaptation of the Kombucha yeast-bacteria community to non-traditional carbon and nitrogen sources, such as citrus waste and spent coffee grounds. This research demonstrated the feasibility of exploiting alternative waste-derived substrates to produce bioactive molecules and bacterial cellulose through static fermentation of Kombucha community. (Manuscript IV submitted). The final part of the thesis focuses on the metagenomic analysis of soil samples from the acidic fumaroles of Vulcano Island, exploring glycosyl hydrolases for diverse biotechnological applications (Manuscript V in preparation). This study revealed a community structure consisting of extremophilic microorganisms capable of thriving in harsh environments and encoding for enzymes potentially involved in lignocellulosic waste degradation, nanocellulose production and bioleaching of metals.

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