Intestinal microbiota plays a crucial role in fish health, with anaerobic bacteria such as Cetobacterium, emerging as key contributors to gut homeostasis. In this study, we report the isolation, genomic characterization, and probiotic potential of Cetobacterium sp. C33, a strain obtained from the intestinal tract of Nile tilapia (Oreochromis niloticus) under anaerobic conditions.
In vitro analyses demonstrated C33’s adaptability to gastrointestinal conditions, including survival in bile salts (0.3%) and low pH. Whole-genome sequencing and annotation revealed a unique genetic profile distinct from closely related species, such as Cetobacterium somerae and Cetobacterium ceti . The genome harbors genes linked to antibacterial activity, intestinal adhesion, and immune modulation, reinforcing its potential as a probiotic. Further comparative genomics confirmed its phylogenetic divergence from previously characterized Cetobacterium species. Also, the absence of toxin-related genes and antibiotic resistance further supports its safety as a probiotic candidate.
To validate its functional application, an in vivo trial was conducted by feed administration of Cetobacterium sp. C33 at 1 × 10⁶ CFU/g to tilapia fingerlings for five days. Results revealed 100% survival, successful intestinal colonization, modulation of the gut microbiota, and immune response regulation, as evidenced by transcriptomic analysis of the head kidney that revealed upregul ation of immune genes such as claudin-8-like Perforin 1, E3 ubiquitin among others.