Sociality and cheating in bacteria

Lecture 13, Myxobacteria

Evolution of social and coordinated group behavior in bacteria

• Swarming motility

• Quorum sensing

• Coordinated cell death

• Sporulation and fruiting body formation

• Synergistic niche subdivision

• Production of “social goods”

• etc

All for the benefit of the group, right?

• Why broadcast a signal for others to profit from your discovery?

• Why allow foreigners to listen in on your conversation?

• How would such behavior evolve?

Individual selection favoring functions that coordinate groups• Inability to produce a beneficial phenotype

in small numbers

• Numbers of neighbors producing a signal may not matter as much as their density

• Common response by several traits to high density or numbers, so selection favors their coordination (and not vice versa)

Quorum sensing

Modes of communication

Evolution of cooperation +/or selfish behavior

• System: Myxococcus xanthus

• Primary Investigator: Greg Velicer

Myxococcus xanthus

http://cmgm.stanford.edu/~kaiserla/about_myxo/about_myxococcus.html

• Adventurous motility• Social motility• Gliding motility• Development of spores

• Motility can be A = adventurous or S = social

• A motility = dependent upon gliding and slime extrusion

• S motility = dependent upon type IV pili

First experimental evo of Myxo

• 12 populations, 6 RifR, shaking flasks, CTT (rich) media.

• Inhibits social contact; mass-action

But the selfish asocial evolved lineages cheat…

Cooperation can evolve along multiple pathways

Cooperation re-evolves using a new system

• cglB = A motility gene

• dsp = fibril producing gene