Biochemical Characterization of Streptomyces sp. I1.2 Secretome Reveals the Presence of Multienzymatic Complexes Containing Cellulases and Accessory Enzymes

Abstract

Two general strategies have been proposed for microbial cellulose degradation: filamentous fungi and aerobic bacteria secrete uncomplexed cellulases, while some anaerobic bacteria produce a cell-associated and large extracellular multienzymatic complex called cellulosomes. By using a combination of 1D-blue native (BN)-PAGE, 2D-BN/SDS-PAGE, zymography, and LC-MS/MS methods, we demonstrate here that Streptomyces sp. I1.2, an aerobic bacterium associated with the land snail Achatina fulica, is able to degrade both crystalline cellulose and sugarcane bagasse through the production of cellulolytic multienzymatic complexes containing different combinations of cellobiohydrolases, endo-glucanases, xylanases, lytic polysaccharide monooxygenases (LPMOs), and peptidases. The assembly and subunit composition of these complexes is specifically affected by the carbon source, while the multienzymatic complexes produced after growth in crystalline cellulose are composed mainly by one cellobiohydrolase and chitinase, in which the complexes produced in response to sugarcane bagasse are more heterogeneous and contain cellobiohydrolases, endo-glucanases, pectate lyases, one LPMO, β-1,3-glucanases, and one xylanase. Our results suggest that Streptomyces sp. I1.2 displays an alternative mechanism for deconstruction of cellulose that depends upon a noncellulosomic association of catalytic subunits into high molecular weight complexes in order to achieve higher catalytic efficiencies.

The Role of Soil Microbial Consortia in Sustainable Cereal Crop Residue Management

“…During this phase, the cellobiose molecule undergoes further hydrolysis reactions, leading to the formation of carbon dioxide, hydrogen, and other organic acids [ 135 ]. Within the bacterial community, some aerobes, such as Cellulomonas , Bacillus , Pseudomonas , and Streptomyces , etc., are recognized as key players in cellulose degradation, contributing significantly to the process of residue decomposition [ 136 , 137 , 138 , 139 ].…”