Identification of Novel Polysaccharide from Myxococcus xanthus and its Function in Developmental Sporulation

Myxococcus xanthus is a Gram-negative bacterium with a complex life cycle that includes vegetative swarming and fruiting-body formation. Previous studies have shown that the exopolysaccharides (EPS) produced by M. xanthus was essential for the developmental process, but the information concerning EPS structure in M. xanthus was lacking. In this study, a novel soluble polysaccharide EPS15M was purified from the extracellular supernatant of M. xanthus DK1622, which was mainly composed of mannose, glucose, glucosamine, and rhamnose. Methylation analysis suggested the prevalence of terminal and 2-linked glycosyl residues, consistent with a branched structure. NMR and liquid chromatography-mass spectrometry analyses confirmed that EPS15M is an α-D-(1,2)-linked mannan backbone with α-D-(1,6)-linked mannose/glucose branches, a structure that differs from any extracellular polysaccharide reported to date from myxobacteria. Besides, EPS15M modestly improves the developmental sporulation of the csgA mutant (approximately 17% of the wild‑type level) at a concentration of 0.1 mg/mL. Collectively, our findings present the first high-resolution structure of a soluble exopolysaccharide from myxobacteria and demonstrate its partial functional compensation of csgA mutant, suggesting that EPS15M may be involved in C‑signal‑mediated developmental sporulation. These results open new avenues for understanding the regulatory role of polysaccharides in the myxobacterial life cycle.