Highly variable domain architecture in carbohydrate-active enzymes highlights Streptomyces as promising resource for rice straw bioconversion

Streptomyces species secrete interesting carbohydrate-active enzymes (CAZymes) with unique domain organization, setting them apart from other soil-dwelling filamentous organisms like filamentous fungi. These Streptomyces CAZymes have potential for lignocellulose degradation, enhancing their application in biotechnological processes like biofuel production. However, the efficacy of Streptomyces enzymes varies based on the strain and enzymes produced. To explore enzymes involved in lignocellulosic rice straw degradation, eight Streptomyces strains were screened for hydrolytic enzyme activity. Three strains C34, MBT40, and MBT70 exhibited significant (ligno)cellulolytic activity, efficiently utilizing rice straw as a carbon source in submerged fermentation. Proteome analysis revealed a diverse array of secreted CAZymes in each strain, illustrating a highly variable hydrolytic enzyme repertoire. Although enzymes with similar functions were identified, the domain organization of the most abundant CAZymes differed significantly among the strains, highlighting the competency of different enzyme cocktails among Streptomyces strains in rice straw degradation.