Antioxidant potential and genomic adaptation of Cetobacterium ceti MaLMAid0298 from the gills of Sebastiscus marmoratus.

Cetobacterium species are common members of fish-associated microbiomes and have been reported from diverse hosts, ranging from freshwater fishes such as carp and tilapia to marine sciaenids. However, their genomic characteristics and roles in oxidative stress defense remain poorly understood. In this study, we present a comprehensive characterization of Cetobacterium ceti strain MaLMAid0298, isolated from gill of the false kelpfish Sebastiscus marmoratus. A high-quality complete genome was assembled using a hybrid approach combining Illumina and Nanopore sequencing, and phylogenomic analysis confirmed its placement within the C. ceti clade. Genomic annotation revealed a thioredoxin-centered redox system adapted to anaerobic environments and complete pathways for cobalamin (vitamin B12) biosynthesis. To further explore its antioxidant potential, we established a genome-wide screening pipeline. Candidate peptides were prioritized using deep learning-based activity prediction models. Although the crude extract exhibited limited direct radical scavenging activity in cell-free assays (DPPH and ABTS), it demonstrated significant intracellular reactive oxygen species (ROS) inhibition (52.43%). These findings provide an integrated genomic and functional view of the antioxidant capacity of C. ceti MaLMAid0298.