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Vermiculite-assisted enhancement and multimodal characterization of exopolysaccharide from Paenibacillus mucilaginosus CCASU-2024-68
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DOI：10.1039/D6NJ01227B.png)
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Abstract
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The exopolysaccharide (EPS) produced by Paenibacillus mucilaginosus CCASU-2024-68 and the enhancement of its production by vermiculite supplementation were investigated. The bacterium was cultivated in glycerol nitrate broth containing different vermiculite levels; and preliminary optimization indicated that 0.5 g L−1 vermiculite at pH 7 and 30 °C for 4 days with agitation at 100 rpm yielded 6.0 g L−1 EPS. To systematically identify the key variables controlling EPS production; a Plackett–Burman design was employed to screen medium components (glycerol; KNO3; K2HPO4; MgSO4; NaCl; CaCO3; vermiculite) and culture conditions (initial pH; inoculum size; agitation speed; and fermentation time). Under the optimal Plackett–Burman condition (Run 2); EPS production increased to 8.44 g L−1 at pH 7 with 30 g L−1 glycerol; 2 g L−1 KNO3; 1 g L−1 K2HPO4; 0.5 g L−1 MgSO4; 1 g L−1 NaCl; 3 g L−1 CaCO3; 1 g L−1 vermiculite; 20% inoculum; agitation at 100 rpm; and 4 days of fermentation. Transmission electron microscopy revealed pronounced morphological alterations in vermiculite-treated cells; including enlarged periplasmic regions; cell wall disintegration; cytoplasmic membrane rupture; and cytoplasmic leakage; indicating a stress-induced response. Scanning electron microscopy showed that control EPS formed a porous; fibrous network; whereas vermiculite-treated EPS exhibited compact; layered; sheet-like structures. Energy-dispersive X-ray analysis indicated substantial changes in elemental composition; with vermiculite-treated EPS enriched in O; Na; P; K; and Ca compared with the control. FTIR and 1H-NMR spectroscopy confirmed typical polysaccharide functional groups and highlighted structural rearrangements upon vermiculite treatment; while HPLC revealed marked shifts in monosaccharide composition; including the appearance of mannose and glucose and the loss of fructose. Overall; these results demonstrate that vermiculite not only enhances EPS yield but also drives significant structural and compositional modifications in the exopolymer; suggesting a mineral-mediated strategy to engineer bacterial EPS for agricultural and industrial applications.
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