Rival colonies of bacteria can produce a lethal chemical that keeps competitors at bay, scientists report this week. By halting the growth of nearby colonies and even killing some of the cells, groups of bacteria preserve scarce resources for themselves, even when the encroaching colony is closely related.
"It supports the notion that each colony is a superorganism, a multicellular organism with it's own identity," said Eshel Ben-Jacob, an adjunct senior scientist at UC San Diego's Center for Theoretical Biological Physics and professor of physics at Tel Aviv University. Ben-Jacob and lead author Avraham Be'er of the University of Texas, Austin, and other colleagues at these institutions report their discovery in the early online edition of the Proceedings of the National Academy of Sciences.
Alone in a dish, colonies of the bacterium Paenibacillus dendritiformis will send branches of cells in all directions. But when forced to share a plate of limited nutrients with another colony, the branching patterns of both colonies become lopsided, leaving a space between the two.
It's not a lack of food that halts the growth. The researchers found nutrients in the gap, but they also found a protein there that wasn't present elsewhere on the dish. When they dabbed a bit of the purified protein on a fresh dish inoculated with P. dendritiformis, the bacteria formed a lopsided colony that shied away from the spot. And the cells at the edge of the colony closest to the suspect protein were dead.
They named the protein "sibling lethal factor," for its ability to kill even closely related colonies derived from a single original colony, and identified its gene. But the gene made a protein that was too large, heavier that the lethal factor by two-thirds and harmless. They concluded that some other factor must be in play.
Rather than guess, or poke about experimentally to figure out what was going on, Ben-Jacob and his colleagues created a model to guide their thinking.
"In physics, we use models to make predictions," Ben-Jacob said, noting that biological models often present what is already understood. The model told them that they should be looking for something that would prune the full-size factor to its smaller lethal form as the colonies began to compete, a factor that might be harmless or even helpful until it reached a certain threshold.
P. dendritiformis also secretes a protein called subtilisin, which promotes growth, except in high concentrations. Subtilisin, which was already known and is available commercially, clipped the full-sized protein to the size of that found between competing colonies. This smaller piece slices the bacteria cells open and spills their contents into the medium, they found.
"Very often, you discover that in order to explain what's going on, you need to imagine mechanisms that are beyond what the biologists have specifically discovered about the system," said Herbert Levine, a physics professor at UC San Diego who co-directs the Center for Theoretical Biological Physics, but was not involved in this study. "In this work, they've succeeded in taking the next step," he said. "They were able find the chemical messenger that is actually playing the role they hypothesized."
Stay prepared and protected with Infection Control Today's newsletter, delivering essential updates, best practices, and expert insights for infection preventionists.
Reducing Hidden Risks: Why Sharps Injuries Still Go Unreported
July 18th 2025Despite being a well-known occupational hazard, sharps injuries continue to occur in health care facilities and are often underreported, underestimated, and inadequately addressed. A recent interview with sharps safety advocate Amanda Heitman, BSN, RN, CNOR, a perioperative educational consultant, reveals why change is overdue and what new tools and guidance can help.
What Lies Beneath: Why Borescopes Are Essential for Verifying Surgical Instrument Cleanliness
July 16th 2025Despite their smooth, polished exteriors, surgical instruments often harbor dangerous contaminants deep inside their lumens. At the HSPA25 and APIC25 conferences, Cori L. Ofstead, MSPH, and her colleagues revealed why borescopes are an indispensable tool for sterile processing teams, offering the only reliable way to verify internal cleanliness and improve sterile processing effectiveness to prevent patient harm.
Getting Down and Dirty With PPE: Presentations at HSPA by Jill Holdsworth and Katie Belski
June 26th 2025In the heart of the hospital, decontamination technicians tackle one of health care’s dirtiest—and most vital—jobs. At HSPA 2025, 6 packed workshops led by experts Jill Holdsworth and Katie Belski spotlighted the crucial, often-overlooked art of PPE removal. The message was clear: proper doffing saves lives, starting with your own.
Unmasking Vaccine Myths: Dr Marschall Runge on Measles, Misinformation, and Public Health Solutions
May 29th 2025As measles cases climb across the US, discredited myths continue to undercut public trust in vaccines. In an exclusive interview with Infection Control Today, Michigan Medicine’s Marschall Runge, PhD, confronts misinformation head-on and explores how clinicians can counter it with science, empathy, and community engagement.
Silent Saboteurs: Managing Endotoxins for Sepsis-Free Sterilization
Invisible yet deadly, endotoxins evade traditional sterilization methods, posing significant risks during routine surgeries. Understanding and addressing their threat is critical for patient safety.