In extremely hard agar, Paenibacillus vortex bacteria congregate into tight, rotating vortices that cut through the growth medium like a circular saw. Living creatures such as bacterial colonies also pattern their growth in response to environmental conditions, in ways that startlingly resemble inanimate objects. For example, microorganisms can create branches according to the same principles governing a snow fern. Molecules of food can, however, bounce randomly through the gel, tending to reach those bacteria that are protruding from the colony, just like water molecules attaching to the spikes of an ice crystal. The bacteria then eat, grow, and split into two, and the protrusion slowly grows into a branch.
Colonies can take up more complex forms because of an extra ingredient - life.
Curls form when Paenibacillus dendritiformis are placed on soft agar. The organisms mutate to a longer form that moves fast but tends to veer to one side, giving rise to the curls. Prof. Ben-Jacob found that if the bacteria are cultured on softer agar, the initially branched pattern changes spontaneously to a curling one that spreads much faster. Under a microscope, each bacterium is seen to become significantly longer when the pattern begins to curl. Ben-Jacob is collaborating with Prof. David Gutnick of the TAU Department of Molecular Microbiology and Biotechnology to try and solve this conundrum.