Shaikh Ibrahim, Ali Fayez Ali (2024) Identification and Exploitation of (Hyper)Thermophilic (Hemi)Cellulases and New Enzymes for Lignocellulosic Waste Products Recycling. [Tesi di dottorato]

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Abstract

Developing sustainable processes based on circular bioeconomy principles has significantly increased the demand for biocatalysts to support greener industrial processes. Therefore, identifying novel enzymes with high stability and specificity compared to existing catalysts is essential for improving current bioprocesses and expanding their applications. Despite several companies have developed enzymatic cocktails for lignocellulosic waste biomass transformation, a significant need remains for more specialized enzymatic blends to target specific polysaccharides. Setting up enzymatic blends of Glycoside Hydrolases (GHs) plays a crucial role in the bioconversion of lignocellulosic biomasses. Therefore, this thesis focuses on identifying and evaluating novel enzymes, particularly GHs, for their potential use in biotechnological applications. Chapter 1 provides a general introduction through a literature review, covering topics such as the circular bioeconomy, lignocellulosic bioconversion, and enzyme discovery, with a focus on carbohydrate-active enzymes. This chapter also highlights the significance of these enzymes in biotechnology. In Chapter 2, the identification, exploitation, and development of a customized enzymatic cocktail for hydrolyzing the polysaccharides present in spent coffee grounds biomass is reported. Several biomass pretreatments have been evaluated, and the pretreated biomass was tested with the cocktail to assess sugar release. Additionally, the potential use of the resulting mannooligosaccharides as prebiotics for gut microbiota has also been reported. This research was conducted in collaboration with Novozymes and the University of Aveiro in Portugal. Chapter 3 explores the discovery of a novel α-L-rhamnosidase from Archaea, identified in a metagenomic data set from the solfatara hot spring Pisciarelli in Naples, Italy. The biochemical characterization of this thermophilic enzyme highlights its potential for industrial applications, particularly in producing rhamnose from natural substrates. It further emphasizes the value of thermostable enzymes in biotechnological processes. Chapter 4 explores new insights into GH116 Family. Expression, purification, biochemical characterization of a new subfamily of GH116, and studying the inhibition of two main inhibitors of this Family. The manuscript is in preparation, and the main results are reported. In conclusion, this thesis contributes to the growing body of research on sustainable bioprocesses by providing novel insights into the discovery and application of thermostable carbohydrate-active enzymes. Developing customized enzyme cocktails for SCG bioconversion presents a promising avenue for waste valorization. Moreover, the discovery of the first archaeal α-L-rhamnosidase gives new possibilities for applying these enzymes due to their characteristics. The appendix highlights two key aspects of the PhD journey: the experience gained during a research stay in a foreign laboratory and the active participation in scientific events such as conferences, meetings, and seminars.

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