Unraveling aerobic cultivable cellulolytic microorganisms within the gastrointestinal tract of sheep (Ovis aries) and their evaluation for cellulose biodegradation

Abstract

Anaerobic cellulolytic microbes in the gastrointestinal tract (GT) of ruminants have been well-documented; however, knowledge of aerobic microbes with cellulolytic activities in the ruminant GT is comparably limited. Here, we unraveled aerobic cultivable cellulolytic microbes in the GT of Ujimqin sheep (Ovis aries) and evaluated the cellulolytic potential of the promising isolates. Twenty-two strains were found to possess cellulose-degrading potential by Congo-red staining and phylogenetic analysis of the 16S rDNA/ITS sequence revealed that all strains belonged to nine genera, i.e., Bacillus, Streptomyces, Pseudomonas, Lactobacillus, Brachybacterium, Sanguibacter, Rhizobium, Fusarium, and Aspergillus. Strains with high cellulolytic activity were selected to further evaluate the activities of various enzymes in lignocellulosic alfalfa hay (Medicago sativa). Among them, isolate Bacillus subtilis RE2510 showed the highest potential for cellulose degradation, considering the high endoglucanase (0.1478 ± 0.0014 IU mL−1), exoglucanase (0.1735 ± 0.0012 IU mL−1), and β-glucosidase (0.3817 ± 0.0031 IU mL−1) after 10-day incubation with alfalfa hay. A significant destruction effect of the cellulose structure and the attachment of B. subtilis RE2510 to the hay were also revealed using a scanning electron microscope. This study expands our knowledge of aerobic cellulolytic isolates from the GT of sheep and highlights their potential application as a microbial additive in the aerobic process of cellulose bioconversion.