Topological defects promote layer formation in Myxococcus xanthus colonies

Area of Science:

• Microbiology
• Biophysics
• Soft Matter Physics

Background:

• Myxococcus xanthus forms complex multicellular structures like fruiting bodies during starvation.
• The initial cell layering process in M. xanthus development is not well understood.

Purpose of the Study:

• To investigate the physical mechanisms underlying cell layer formation in Myxococcus xanthus.
• To understand how cell motility and interactions contribute to multicellular development.

Main Methods:

• Utilized confocal three-dimensional imaging to observe bacterial cell behavior.
• Developed a physical model of the bacterial colony as an active nematic fluid.

Main Results:

• Observed that M. xanthus cells form densely packed, aligned layers exhibiting active nematic liquid crystal behavior.
• Identified point defects with half-integer topological charge where cell alignment deviates.
• Found that new cell layers form at +1/2 defects and holes open at -1/2 defects.
• Model predicted cell influx at +1/2 defects and outflux at -1/2 defects, matching experimental observations.

Conclusions:

• Cell motility and mechanical interactions drive the formation of cell layers at topological defects.
• Topological defects act as nucleation sites for multicellular structure formation in M. xanthus.
• This mechanism provides insight into the initial seeding of fruiting bodies.