Evaluation of the biotechnological potential of the cellulolytic system of Xanthomonas axonopodis pv. citri: a structural, functional and applied approach

Abstract

Due to the heterogeneity and recalcitrance of lignocellulosic biomass its complete and efficient degradation is a challenge to be overcome aiming the economic viability of some bioprocesses, such as the cellulosic ethanol. One of the main factors that contribute for this is the absence of efficient and low cost enzymatic cocktails. Plant pathogens found in Xanthomonadaceae family, particularly, species Xanthomonas axonopodis pv. citri (XAC), that causes citrus canker, affecting several citrus cultivars, and resulting in significant economic losses to the country's agriculture, contains a large repertoire of genes related to the expression of glycoside hydrolases (GHs). The XAC, although it does not perform massive maceration of the plant cell wall, has in its genome more than 100 GHs genes spread into 45 families, comparable in number to other organisms specialized in the lignocellulosic biomass degradation, such as Ruminococcus albus and Clostridium cellulolyticum. Therefore, the aim of this postdoctoral project is to evaluate the GHs still unexplored XAC involved in cellulose degradation (family GHs 3, 5, 8 and 9). According to CAZy database, of the more than 13,971 sequences predicted to be GHs 5, 8 and 9, only 5.6 % of this total has been biochemically characterized, and even less from a structural view. It is understand that the knowledge of only a few members is not enough to reveal all the functional diversity contained in these families, even more if they exhibit a range of activities and modes of action. In this context, we hope to contribute to the greater mechanistic understanding of modes of action found in these families, using a multidisciplinary approach involving biochemical, enzymatic kinetics, immobilization, and structural analysis (X-ray crystallography, DLS, SAXS and Circular Dichroism). In addition, this project aims at one of the main GH families that are present in the cellulose-degrading commercial cocktails, family 3. We intend to evaluate the role of the PA14 domain present in one GH3 obtained from XAC, an enigmatic domain still poorly characterized in the literature to family 3; in addition to investigating the functional (biochemical and glucose tolerant) and structural differences between GH3 belonging to this plant pathogen.