Lactic acid bacteria and yeast co-culture system: Mechanism of quorum-sensing regulation on the high yield of exopolysaccharides in Weissella confusa.

The low yield of exopolysaccharides (EPS) produced by lactic acid bacteria (LAB) restricts their industrial application. To overcome this limitation, a single-factor optimization strategy was applied to develop co-culture system involving Weissella confusa P2 and Candida shehatae. This approach resulted in 48.68 % increase in EPS yield compared to mono-culture conditions. Structural analyses via high-performance liquid chromatography (HPLC), methylation analysis, nuclear magnetic resonance (NMR), and fourier transform infrared spectroscopy (FT-IR) revealed that the co-culture EPS was high-molecular-weight dextran (7.62 × 106 Da), consisting primarily of α-(1 → 6)-linked glycosidic backbone with occasional α-(1 → 3) branching. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated smooth sheet-like morphology and amorphous structure. The co-culture EPS exhibited favorable functional properties, including high water solubility index (91.35 ± 1.48 %), water holding capacity (576.93 ± 13.59 %), thermal stability (Td = 311.1 °C), and antioxidant activity (with high ABTS radical scavenging rate of 45.1 ± 0.20 %). Fermentation profiling revealed significant positive correlation between EPS production and bacterial density, glucansucrase activity, and autoinducer-2 (AI-2) fluorescence intensity. Based on correlation analyses, these results suggest that the presence of C. shehatae may trigger quorum sensing (QS) response, stimulating the release of AI-2 signaling molecules that enhance microbial growth and consequently promote EPS biosynthesis.