Biosynthesis of exopolysaccharide and structural characterization by Lacticaseibacillus paracasei ZY-1 isolated from Tibetan kefir.

Exopolysaccharide (EPS) was produced by Lacticaseibacillus paracasei ZY-1 isolated from Tibetan kefir grains, and the preliminary structure of two EPS fractions (EPS1 and EPS2) was investigated. NMR analysis revealed that the backbone of higher producing EPS1 was consisted of →6)-α-D-Manp-(1→, →2,6)-α-D-Glcp-(1→, α-D-Manp-(1→, →2)-α-D-Glcp-(1→, →3)-α-D-Manp-(1→, →6)-α-D-Glcp-(1→. Furthermore, an eps gene cluster that encodes the glycosyltransferase and relevant proteins for EPS biosynthesis was identified on the basis of bioinformation analysis of the complete genome. RT-qPCR results indicated that wzd (ZY-1_2260) and wze (ZY-1_2259) might be essential genes involved in EPS production. Meanwhile, the synthetic mechanism of EPS1 in L. paracasei ZY-1 was further proposed. Besides, the crude and purified EPS showed certain scavenging activities against DPPH, hydroxyl and ABTS radicals. Results provided a better understanding of EPS biosynthesis in L. paracasei ZY-1 at the gene level.