Preparation of Sphingan Oligosaccharides by SpnR Hydrolysis and Their Prebiotic Effects on Intestinal Flora

Oligosaccharides have the potential to act as prebiotics and can be obtained by enzymatic hydrolysis of polysaccharides. Sphingans are exopolysaccharides, including gellan, welan, and diutan, which are synthesized by the genus Sphingomonas. Sphingan lyase (SpnR) has attracted a great deal of interest due to its ability to produce oligosaccharides through the degradation of sphingans. However, there are few reports on the catalytic mechanism and hydrolysate analysis of SpnR. Here, SpnR from Sphingomonas sp. HT-1 was heterologously expressed in Escherichia coli. The optimal temperature and pH of the purified SpnR were 35 °C and pH 7.2, respectively. SpnR has good alkali resistance and a relatively mild optimum temperature. Na⁺ and Fe³⁺ increased SpnR activities, in contrast to Zn²⁺ and EDTA. SpnR could degrade sphingans, and the most suitable substrate was welan. Analysis of the cleavage pattern revealed that SpnR acts specifically on the β-1,4-glycosidic bond to obtain minimum trisaccharide sphingan oligosaccharides (SpnOS). The gut microbiota in vitro showed that SpnOS caused a substantial modification in the intestinal microbiota, characterized by an augmented proliferation of beneficial bacterial populations, notably Bacteroides and Lactobacillus.