Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 16 3 2024 06 19 389 400 EN Seyyed Ehsan Ghiasi Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran; Research Group of Environmental Stress in Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran Maryam Gheibipour Department of Animal Science, Faculty of Agriculture, University of Birjand, Birjand, Iran; Department of Environmental Health Engineering, Environmental Technologies Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran Hossein Motamedi Department of Biology, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, Iran; Biotechnology and Biological Science Research Center, Shahid Chamran University of Ahvaz, Ahvaz, Iran Mudasir Dar Biofuels Institute, School of Environment & Safety Engineering, Jiangsu University, Jiangsu, China 2023 12 11 2024 04 22 Background and Objectives: Rumen microbiologists are looking for new probiotics to improve the digestibility of livestock diets. This study intended to screen and evaluate the ruminal cellulolytic bacteria (CBs) and their potential application as probiotics. Materials and Methods: Microbial culture and molecular techniques performed to isolate CBs from the rumen of camels, deer and rams. Their antibacterial and antibiogram tests were done using disc diffusion method. Their potential to degrade cellulose, starch, tannin and protein were investigated using clear zone halo, and spectrophotometric techniques. Bilious, saline, and acidic broth media were used to study the resistance of isolates in intestinal conditions. Results: The phylogenetic analysis revealed that the strains belonged to Firmicutes and Proteobacteria phyla, Citrobacter murliniae, Ornithinibacillus bavariensis, C. braakii, and Bacillus subtilis. The highest cellulase (CAS) activity was recorded by C. murliniae Dez wildlife13A (2.98 UmL-1), whereas C. braakii Loot desert 111A (1.14 Uml-1) was produced the lowest enzyme. The isolates were highly resistant to synthetic conditions of intestine (pH 2.5-3.5, bile 0.3-2%), as well as tolerated higher concentrations of NaCl (up to 10%). They effectively inhibited standard pathogen strains, and showed sensitivity to the used antibiotics. Conclusion: This study reports the cellulolytic O. bavariensis Tabbas desert 32A for the first time from the rumen, which will have potential biotechnological applications. https://ijm.tums.ac.ir/index.php/ijm/article/view/4514 https://ijm.tums.ac.ir/index.php/ijm/article/download/4514/1681