Abstract

Bacterial symbionts of marine algae are known to be rich in bioactive compounds that can promote health, including immunostimulatory effects. Thus, this study aimed to isolate, purify, and hydrolyze bioactive protein-producing bacterial symbionts associated with marine algae. The isolated bioactive proteins were identified and evaluated for biological activities, including antioxidant and immunostimulant assays, as well as hydrolysis and ultrafiltration. Their immunostimulant activity was further tested in Wistar rats. Intracellular proteins were isolated using ammonium sulfate fractionation at saturation levels of 0–40% (F1), 40–60% (F2), 60–80% (F3), and 80–100% (F4). Antioxidant activity assessed using the DPPH method showed that the F2 (30′) protein hydrolysate fraction and the intracellular F2 (30′) ultrafiltration fraction (5 kDa) had IC₅₀ values of 219.11 and 421.06 μg/mL, respectively. Toxicity testing using the brine shrimp lethality test (BSLT) revealed LC₅₀ values of 10.18 and 38.42 μg/mL, respectively, indicating toxicity. Immunostimulant activity, analyzed using a one-way ANOVA, showed phagocytosis index values of 1.7491 and 1.0082, respectively, demonstrating that the protein hydrolysate fraction exhibited stronger immunostimulant activity than the ultrafiltration fraction.

Key words: Antioxidants, Bioactive proteins, Eucheuma spinosu, Epiphytic bacteria, Immunostimulants, Marine algae