Myxococcus Xanthus

Myxococcus xanthus (Greek: xanthos, ξανθος, "yellow") colonies exist as a self-organized, predatory, saprotrophic, single-species biofilm called a swarm. Myxococcus xanthus, which can be found almost ubiquitously in soil, are thin rod shaped, gram-negative cells that exhibit self-organizing behavior as a response to environmental cues. The swarm, which has been compared to a "wolf-pack," modifies its environment through stigmergy. This behavior facilitates predatory feeding, as the concentration of extracellular digestive enzymes secreted by the bacteria increases. M. xanthus is a model organism for studying development, the behavior in which starving bacteria self-organize to form fruiting bodies: dome shaped structures of approximately 100,000 cells. These swarms differentiate into metabolically quiescent and environmentally resistant myxospores over the course of several days. During this process of self-organizing, dense ridges of cells move in traveling waves (ripples) that grow and shrink over several hours.

A swarm of M. xanthus is a distributed system: a population of millions of identical entities that communicate among themselves in a non-centralized fashion, thus behaving as a single entity. The cells within the swarm form a collective, exhibiting coordinated movement through a series of signals to create dynamic patterns in response to environmental cues. One of these behaviors, development (mentioned above), is controlled through a cascade, or series, of transcriptional regulators (TR) that control downstream gene expression. It has been proposed that all emergent, or self-organizing, behavior in M. xanthus is under this type of control.