Genomic and Functional Characterization of the Marine Spongeassociated Bacillus stercoris Strain 84-5 Reveals...

Sponge-associated bacteria are recognized as prolific sources of bioactive metabolites. Although members of the promising phylum Bacillota are commonly found in marine sponges, their genomic potential remains largely unexplored. This study aims to investigate the Bacillus stercoris 84-5 strain isolated from the sponge Darwinella sp. and evaluate its biosynthetic and enzymatic potential.

Whole-genome sequencing and comparative analyses of biosynthetic gene clusters (BGCs) were conducted. In parallel, in vitro assays were performed to evaluate biosurfactant activity (emulsification and surface tension) and enzymatic profiles.

The 84-5 genome (4.12 Mbp) encodes at least 11 potential BGCs. In particular, a nonribosomal peptide synthetase (NRPS) cluster showed 82% similarity to a surfactin gene cluster from Bacillus velezensis FZB42, and a corresponding surface tension of 27.44 ± 0.33 mN/m. Genes related to the production of carbohydrate-active enzymes (CAZymes) were also detected. In vitro assays confirmed the production of agarase, alginate lyase, and peptidase, with an enzymatic index (EI) > 3.5 for agarase and peptidase. Comparative analyses revealed shared BGC families among sponge-associated Bacillota genomes.

The high diversity of putative bioactive BGCs found, including many shared among sponge-associated Bacillota, suggests biosynthetic pathways that are likely to play important ecological roles within the sponge holobiome. Additionally, the abundance of enzymes probably reflects the metabolic versatility required for life in marine niches.

The marine B. stercoris 84-5 exploration thus reveals a promising candidate for exploiting both biosurfactant and enzymatic capabilities, shedding light on the understudied potential of sponge-associated Bacillota.