Non-pathogenic Oomycetes as an untapped source of β-glucan: yield, structure, and bioactivity across Pythium and Phytopythium isolates from Thailand

Abstract Oomycetes possess β-(1,3)/(1,6)-glucan-rich cell walls that are structurally distinct from the chitin-based walls of true fungi, yet this taxon has never been systematically surveyed as a source of bioactive polysaccharides. Building on our previous molecular survey of Pythium and related genera isolates from some habitats in Thailand, we screened 11 hypo-virulent isolates for β-glucan yield, structure, and preliminary bioactivity. Total β-glucan content ranged from 24.30 to 32.70% (w/w) under standard V8 broth culture, and glucose supplementation (4%) raised yield in Pythium catenulatum CHS-10 to 63.58% (w/w) — exceeding both the pathogenic congener Pythium insidiosum and the commercial Saccharomyces cerevisiae reference used here. ATR-FTIR and NMR spectra were consistent with a conserved β-(1,3)/(1,6)-glucan backbone across all 11 isolates, extending to non-pathogenic Oomycetes a structural signature previously reported only for a pathogenic species. As motivating evidence for further study, the extracts also inhibited Ralstonia solanacearum , Bacillus subtilis , and Xanthomonas oryzae in disc-diffusion assays, showed dose-dependent DPPH/ABTS radical-scavenging activity, and elicited scopoletin accumulation in durian seedlings. These results identify non-pathogenic Oomycetes as a quantitatively competitive, previously unsurveyed β-glucan resource, and establish a screening-level foundation for the mechanistic and dose–response studies needed to develop it further.