*3.3. Methylation Analysis*

Glycosyl-linkage positions were determined as described in [20]. The native EPS was carboxyl-reduced by treatment with N-cyclohexyl 1-N'[ ®(N-methyl-morpholino)-ethyl] carbodiimide p-toluene sulfonate and with NaBD4 for 4 h at room temperature [21]. After dialysis against distilled water, hydroxyl groups were methylated using 2.5 N butyl lithium in hexanes and methyl iodide in DMSO [22]. The methylated compounds were extracted with CH2Cl2. The methylated products were then hydrolyzed in 2 M TFA for 2 h at 120 ◦C, then reduced with NaBD4 in a NH4OH solution for 30 min at 80 ◦C, and finally acetylated with 200 μL of 1-methyl imidazole and 2 mL of pyridine for 10 min at room temperature. GLC-mass spectrometry (MS) was performed on an Agilent instrument fitted with a high-performance 5 ms capillary column (Agilent, 0.25 mm × 30 m). The temperature program was 90 ◦C for 1 min, 90 ◦C to 300 ◦C at 5 ◦C/min, 300 ◦C for 1 min. Ionization was carried out in electron impact mode (EI, 70 eV).

#### *3.4. Determination of Absolute Configuration*

Assignment of absolute configuration of monosaccharide residues was adapted from the method of Gerwig [23,24]. A quantity of 2 mg of polysaccharide was dissoved in 500 μL of 4N TFA and maintained, in sealed glass tubes, for 4 h at 100 ◦C. After cooling, TFA was evaporated under a flux of nitrogen. Next, 500 μL of (S)-(+)-2-butanol and a drop of 13N TFA were added to the dried sample and the hermetically sealed glass tube was kept at 8 hours at 80 ◦C. Butanol and TFA were evaporated under nitrogen. Butylglycosides samples were then re-N-acetylated, converted to their corresponding trimethylsilyl derivatives and analyzed by GLC according to the protocol described in Section 3.2. for monosaccharide analysis.

#### *3.5. Molecular Weight Determination*

The molecular weight of VA-EPS was determined by high-performance size-exclusion chromatography (HPSEC) using an eighteen-angle light scattering detector, coupled with refractive index detection and specific refractive index increment dn/dc (DAWNTM HELEOS, Wyatt). Elution was performed on Shodex OHpak SB-805 HQ and OHpak SB-806 HQ placed in series (Phenomenex, exclusion limit <2 × 10<sup>7</sup> g/mol) with 0.1 M NaNO3 as the eluent. To calculate the molecular mass, the dn/dc value used was 0.145 mL/g. The polydispersity index was calculated from the Mw/Mn ratio.

#### *3.6. Acid Hydrolysis and Oligosaccharides Purification*

VA-EPS underwent mild acid hydrolysis. A quantity of 300 mg of polysaccharide was solubilized in 75 mL of 0.1 M TFA and heated at 100 ◦C for 90 min or 300 min, respectively. After neutralization with 8N NH4OH, the salts were eliminated by adding five volumes of acetone. The precipitate that contained the oligosaccharides was recovered by centrifugation. The pellet was resuspended in 2 mL of distilled water and the oligosaccharides were fractionated by size exclusion chromatography using a SEC Toyopearl HW-40 column (5 × 100 cm, Tosoh, exclusion limit <10<sup>4</sup> Da) with 0.1 M (NH4)2CO3 as the eluent.
