Extraction, statistical optimization, and immunomodulatory activity of exopolysaccharide from seaweed-associated Bacillus megaterium DSKPDF CMST3

Seaweed-associated Bacillus megaterium DSKPDF CMST3 was screened for EPS production and its production was statistically optimized using central composite design and response surface methodology. Structural characterization of EPS was investigated by FT-IR and NMR spectroscopy. Furthermore, morphological structure of the EPS investigated by SEM demonstrated it to be less porous with flake-like structure. The XRD and TGA observations revealed the semi-crystalline nature of EPS. EPS-supplemented diet significantly enhanced immunological and hematological parameters in Labeo rohita. The immune gene expression (IL10, IL-1β, and TGFβ) were significantly upregulated in lymphoid organs of the fish. Moreover, the dietary supplementation of EPS showed significantly (p < 0.001) higher survival rates of DII (71%) compared with basal diet (56.40%) fed fish against Aeromonas hydrophila infection. The result suggests that the exopolysaccharide can be applied as a fish feed supplement to enhance fish immunity and disease resistance against A. hydrophila.