Mutagenesis Engineering Reveals Multiple Catabolic Pathways of Xanthan

Exploring the microbial catabolism of complex polysaccharides like xanthan (XG) is crucial for improving oligosaccharide production and their use in food and agriculture. Through mutagenesis, we obtained a mutant bacterium, Microbacterium sp. YXT11, which rapidly utilizes XG and efficiently accumulates oligoxanthan (XOG). Further process optimization led to an 8.67-fold increase in XOG productivity. Additionally, XOG exhibited a narrow polydispersity, along with enhanced antioxidant (IC50 = 1.25 mg/mL for hydroxyl radical scavenging) and immunomodulatory properties (effective at 25 μg/mL). Furthermore, the mechanism underlying the efficient XG catabolism in YXT11 was elucidated, involving the downregulation of the flagellar assembly pathway for metabolic adjustment and the switching of the xanthan catabolic pathway from the repressed XG-specific PUL to a pathway containing CAZymes with similar functions as well as the upregulation of the mannitol-specific phosphotransferase system. These findings deepen our understanding of xanthan catabolism and provide a molecular basis for its efficient degradation, aiding its practical valorization.