Staiano, Ivana (2025) EXTREMOPHILES - GREEN AND ECOFRIENDLY COMPOUNDS PRODUCERS FOR NEXT GENERATION INDUSTRIAL BIOTECHNOLOGY. [Tesi di dottorato]

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Abstract

This PhD thesis investigates how microbial diversity and metabolites can enhance plant resilience and promote sustainable agriculture. It is divided into three parts connecting microbial ecology, plant physiology, and biotechnology. Part I explores plant–microbe interactions under abiotic and biotic stresses. In Chapter II, from the roots of the halophytic plant Pancratium maritimum, fifteen bacterial strains tolerant to salinity and heat were isolated. A three-member consortium, composed by Serratia marcescens ERA6, Enterobacter cloacae ERA9, and Bacillus proteolyticus ESOB2, significantly improved wheat growth under combined salinity and heat, increasing biomass, pigments, and antioxidant activity. Another study, reported in Chapter III, focused on an extremophilic fungus, Talaromyces pseudofuniculosus FRA, isolated from an acidic site (“Piccolo Inferno”). This strain is highly resistant to salt and metals, it produced hydrolytic enzymes and strongly promoted soybean growth under copper and salinity stress, suggesting its potential as a multi-tolerant biofertilizer. Additional work identified microbial metabolites with antifungal activity: metacycloprodigiosin from Streptomyces alboflavus (Chapter V - Appendix), and drimane-type sesquiterpenes from Aspergillus xerophilus (Chapter VI - Appendix), effective against major phytopathogenic fungi. Together, these results show that stress- adapted microorganisms and their metabolites can simultaneously promote growth and defend plants. Part II (Appendix) focuses on Bacillus subtilis spores as models of biological resilience. By deleting the spsA–L operon responsible for polysaccharide synthesis, spores were found to expose the triterpenoid curcumene, reducing hydrophilicity and identifying lipids as key surface components. Part III (Appendix) develops a circular bioprocess converting inulin from Cynara cardunculus roots into polyhydroxyalkanoates (PHAs). Overall, this thesis demonstrates that exploiting microbial systems, from rhizospheric bacteria and extremophilic fungi to bacterial spores, offers powerful, eco-friendly tools for plant stress tolerance, soil restoration, and bioplastic production, bridging basic microbiology with sustainable innovation.

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