Myxococcus xanthus

Myxococcus xanthus has become the primary model for bacterial social behavior because it displays the full range of myxobacterial cooperative phenomena: coordinated swarming predation, regulated development, and multicellular fruiting body formation. When food is abundant, M. xanthus cells swarm together across surfaces in coordinated waves, collectively hunting and lysing other bacteria. When food runs out, thousands of cells aggregate into fruiting bodies where some differentiate into stress-resistant spores while others sacrifice themselves to build the structure.

The predatory swarming demonstrates collective behavior emergent from individual cell actions. Each cell follows simple rules—move, reverse periodically, align with neighbors—yet together they generate complex swarm patterns that concentrate cells at prey colonies. Secreted enzymes and antibiotics from the swarm overwhelm prey defenses that would defeat individual attackers. The swarm functions as a hunting pack where coordination multiplies individual capabilities.

Fruiting body development reveals even more sophisticated social organization. When starvation signals trigger aggregation, cells stream toward aggregation centers, then pile into mounds that mature into species-specific structures. Approximately 10-20% of cells become spores; the remainder die, contributing their cellular contents to spore maturation. This programmed cell death raises evolutionary questions about why individuals sacrifice for the group. Research shows that M. xanthus cells preferentially cooperate with genetically similar neighbors, maintaining cooperation through kin selection. Social behavior isn't random—it's targeted toward relatives who share genes.