Recent advances in glycobiotechnology show that bacterial exopolysaccharides (EPS) presenting glycosaminoglycan (GAG)-like properties can provide a valuable source of bio-active macromolecules for industrial applications. The HE800 EPS, named diabolican, is a marine-derived anionic high-molecular-weight polysaccharide produced by Vibrio diabolicus CNCM I-1629 which displays original structural features close to those of hyaluronic acid. We investigated the impact of carbon and nitrogen substrates on both Vibrio diabolicus growth and diabolican production. Both substrates were screened by a one-factor-at-a-time method, and experimental designs were used to study the effect of glucose, mannitol, and ammonium acetate various concentrations. Results showed that the medium composition affected not only the bacterium growth and EPS yield, but also the EPS molecular weight (MW). EPS yields of 563 and 330 mg L-1 were obtained in the presence of 69.3 g L-1 glucose and 24.6 g L-1 mannitol, respectively, both for 116.6 mM ammonium acetate. MW was the highest, with 69.3 g L-1 glucose and 101.9 mM ammonium acetate (2.3 × 106 g mol-1). In parallel, the bacterial maximum specific growth rate was higher when both carbon and nitrogen substrate concentrations were low. This work paves the way for the optimization of marine exopolysaccharide production of great interest in the fields of human health and cosmetics.

exopolysaccharide, production, molecular weight, Marine bacterium, central composite design, Vibrio diabolicus, yield

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@H](O)[C@@H](CO)O[C@@H](O[C@@H]2[C@@H](C(=O)O)O[C@@H](O[C@@H]3[C@@H](C(=O)O)O[C@@H](O[C@H]4[C@@H](CO)O[C@H]([*])[C@H](NC(C)=O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)[C@@H]1NC(C)=O

758.636 g/mol (C₂₈H₄₂R₂N₂O₂₂, R = next and previous repeats, not counted in mol weight)

The bacterial strain HDE-9 was isolated from sauerkraut and identified as Levilactobacillus brevis. An exopolysaccharide (EPS) was isolated and purified from L. brevis HDE-9, and a preliminary investigation of its structural characteristics and biological activity was conducted. The molecular weight of the EPS was >1.0 × 106 Da. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy revealed that the EPS was composed of α-(1→6) linked D-glucopyranose units. X-ray diffraction (XRD) data on the EPS revealed its non-crystalline amorphous structure. Scanning electron microscopy (SEM) of the EPS revealed a smooth surface with sheet structures. The EPS exhibited the high value in thermal stability, water solubility, water holding capacity (WHC), and emulsification activity (EA). The water contact angle of the EPS revealed relatively high hydrophobicity in the presence of sucrose. The EPS also showed a strong milk solidification capacity in a dose-dependent manner. The EPS could significantly improve the texture of yoghurt, indicating its potential application as a functional starter in the production of fermented dairy products.

structure, exopolysaccharide, yoghurt, characteristics, Levilactobacillus brevis

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
	aDGlcp	97.75	71.36	73.34	69.54	69.54	65.61


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
	aDGlcp	4.90	3.58	3.75	3.89	3.89	3.73-3.98


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
	aDGlcp	97.75/4.90	71.36/3.58	73.34/3.75	69.54/3.89	69.54/3.89	65.61/3.73-3.98

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]OC[C@H]1O[C@H]([*])[C@H](O)[C@@H](O)[C@@H]1O

162.141 g/mol (C₆H₁₀R₂O₅, R = next and previous repeats, not counted in mol weight)