Biological systems and soft materials:

Future directions in statistical physics

A symposium on the interface of statistical physics, biology, and chemistry

Department of Physics, Virginia Tech

Blacksburg, Virginia, USA

March 6 and 7, 2004

Invited talk:

Yi Jiang

Theoretical Division, Los Alamos National Laboratory

Rippling and aggregation in myxobacteria: A cellular automata modeling

Myxobacteria are social bacteria which swarm, feed and develop cooperatively. When starved, myxobacteria undergo a complex multi-step process of alignment, rippling, streaming and aggregation that culminates in the formation of a fruiting body. Understanding the fruiting body formation in myxobacteria will provide new insight into collective cell motion since it depends on contact-mediated signaling. We model myxobacteria rippling and aggregation with Lattice Gas Cellular Automata (LGCA) models based entirely on short range (non-chemotactic) cell-cell interactions. Local rules result in ripple and aggregate patterns that resemble those observed in experiments. We examine various hypotheses for the formation of ripples and find the relation between contact signaling and cell density. We also find a novel two-stage process of aggregation mediated by transient streams; aggregates are stable against even very large perturbations, forming a 'stable attractor' in the area-density phase space. Noise in individual cell behavior increases the effects of streams and results in larger, more stable aggregates.