Compost-derived thermophilic microorganisms producing glycoside hydrolase activities as new potential biocatalysts for sustainable processes

Abstract

Background The management of the organic waste recycling process determines the interest in the thermophiles microorganisms involved in composting. Although many microbial enzymes have been isolated and studied for their industrial and commercial uses, there is still a continuous search for microorganisms which could synthesize industrially feasible enzymes, especially when the microbial diversity of cow dung itself makes a potential source of biotechnological enzymes. Results The composting process studied at the Experimental Station of the University of Naples Federico II (Castel Volturno, Caserta, Italy) was characterized by fresh saw dust 40%, bovine manure 58%, and 2% mature compost as raw organic substrates, and its thermophilic phase exceeded a temperature of 55 °C for at least 5 days, thus achieving sanitation. Six microbial strains were isolated and designated as follow: CV1-1, CV1-2, CV2-1, CV2-2, CV2-3 and CV2-4. Based on 16S rRNA gene sequence, HRMAS–NMR spectroscopy, and biochemical investigations, they were ascribed to the genera Geobacillus and Bacillus. All the microbial isolates were qualitatively screened on plates for the presence of hydrolytic activities, and they were quantitatively screened in liquid for glycoside hydrolase enzymes in the extracellular, cell-bound, and cytosolic fractions. Based on these results, strains CV2-1 and CV2-3 were also quantitatively screened for the presence of cellulase and pectinase activities, and pH and temperature optimum plus thermostability of cellulase from CV2-1 were analyzed. Conclusions The isolation and the identification of these thermophilic microorganisms such as Geobacillus toebii, Geobacillus galactosidasius, Bacillus composti, Bacillus thermophilus and Aeribacillus composti have allowed the study of the biodiversity of compost, with emphasis on their primary metabolome through an innovative and underutilized technique, that is HRMAS–NMR, also highlighting it as a novel approach to bacterial cell analysis. Subsequently, this study has permitted the identification of enzymatic activities able to degrade cellulose and other polymeric substrates, such as the one investigated from strain CV2-1, which could be interesting from an industrial and a biotechnological point of view, furthermore, increasing the knowledge for potential applicability in different industrial fields as an efficient and environmentally friendly technique. Graphical Abstract