Data Sheet 1_A novel bacterial symbiont in the seaweed Gracilaria tenuistipitata and its promising anti-inflammatory and antiproliferative potential in relation to special secreted metabolites.docx

The results show that S.100 belongs to a Bacillus species reported for the first time to be associated with Gracilaria tenuistipitata. The EtAc extract of its culture selectively inhibited proliferation of human cervical (HeLa, IC₅₀ = 31.87 μg/mL) and hepatocellular (HepG2, IC₅₀ = 63.8 μg/mL) carcinoma cell lines, with substantially lower cytotoxicity toward normal human embryonic kidney cells (HEK 293T, IC₅₀ = 181.1 μg/mL).

At 120 μg/mL, the extract also suppressed lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages. Toxicological assessment in zebrafish embryos revealed no developmental abnormalities below 200 mg/L and an LC50 of 421.6 mg/L at 96 h, consistent with a favorable safety profile. Bioactivity-guided fractionation, coupled with LC-HRMS analysis, putatively annotated 16 specialized metabolites in the most active fraction (fraction 4), including noteworthily bioactive cyclic lipopeptides (surfactins B and C), β-carboline and quinoline alkaloids (norharmane, harmane, and quinoline-4-carboxylic acid), and phenolic acids (gallic and 2,3-dihydroxybenzoic acids).

Together, these findings show exciting biopharmaceutical application potential of S.100 and highlight macroalgal endophytes as a promising chemical source for the discovery of marine-derived therapeutics.</p>