Regulated exopolysaccharide production in Myxococcus xanthus

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Myxococcus xanthus fibrils are cell surface structures with significant polysaccharide and protein content.
• Fibril production is crucial for M. xanthus cell-cell interactions and development.

Purpose of the Study:

• To investigate the regulation of M. xanthus polysaccharide production under various conditions.
• To understand the role of divalent cations and the phosphoenolpyruvate carboxykinase (Pck) enzyme in fibril synthesis.

Main Methods:

• Analysis of wild-type and mutant M. xanthus strains under different growth phases and cation concentrations.
• Measurement of exopolysaccharide levels and phosphoenolpyruvate carboxykinase (Pck) activity.
• Transmission electron microscopy (TEM) of freeze-substituted cells to visualize fibril structure.

Main Results:

• Wild-type exopolysaccharide production significantly increases during stationary phase and upon Ca2+ addition, correlating with enhanced Pck activity and cell agglutination.
• Most fibril-deficient mutants showed impaired stationary-phase or Ca2+-dependent polysaccharide production, but Pck regulation remained largely intact.
• Strontium (Sr2+) effectively substituted for calcium (Ca2+) in stimulating polysaccharide production and was essential for fruiting-body formation.

Conclusions:

• M. xanthus polysaccharide production is tightly regulated by growth phase and divalent cations like Ca2+ and Sr2+.
• The Pck enzyme's activity is linked to fibril polysaccharide synthesis, suggesting its involvement in this regulatory pathway.
• Mutational analysis indicates that specific genetic factors control fibril polysaccharide production, with some mutants retaining the capacity for synthesis.