Bacteria Wars: Kinship in the Swarm

A single, microscopic bacterium divides and expands into a visible colony that can further organize into dynamic structures, from swarming patterns to biofilms. Microbiologist Scott Chimileski at the Marine Biological Laboratory combines microscopy and time-lapse photography to capture the visual beauty of these intricate features.

Chimileski’s interest in imaging began during graduate school and deepened while working as an imaging specialist during his postdoctoral work in Roberto Kolter’s lab at Harvard Medical School. “Roberto had over 7,000 strains in his freezer. He had a very eclectic lab and promoted people bringing in all sorts of different projects.”

Chimileski worked with various organisms, but one project remains memorable. “I did a time-lapse of swarming [in Bacillus subtilis], which is a really, really cool phenomenon,” remarked Chimileski. B. subtilis, a model biofilm-forming soil bacterium, spreads—or swarms—across surfaces to access nutrients. In 2015, Kolter’s team and colleagues found that B. subtilis exhibits kin discrimination, wherein bacteria recognize and cooperate only with genetically similar strains while colonizing new areas.¹

The team grew different B. subtilis strains side by side on a Petri dish. The above image that Chimileski captured shows a B. subtilis colony that looks like a bacterial moon, extending thin tendrils outward across the dish. Related strains merged, while distant strains secreted antibiotics to form borders between each other.

Next, they aimed to elucidate the mechanism behind this behavior. Through genetic and transcriptomic analyses, the team found that B. subtilis expressed genes for contact-dependent inhibition proteins and antimicrobial compounds to block non-kin.²

Chimileski continues to uncover the hidden beauty and complex behaviors of bacteria, revealing how they organize, interact, and establish boundaries in their microscopic world.