Scientists Discover Toxic “Umbrella” Proteins Used by Soil Bacteria in Microbial Warfare

Researchers have found that soil bacteria called Streptomyces release toxic proteins shaped like umbrellas to fight off their rivals, especially those of their own species. The discovery of these umbrella toxin particles, along with details about their structures, makeup, and how they work, was published on April 17 in the journal Nature.

Streptomyces Bacteria: A Rich Source of Antibiotics

The umbrella toxin proteins are just the latest example of the various attacks these bacteria use against their microscopic enemies. The crowded and diverse bacterial communities they live in are full of antimicrobial attacks, counterattacks, and defenses. Many antibiotics used in medicine come directly from, or are inspired by, molecules that bacteria use against each other in their natural environments. Streptomyces’ chemical weapons against their competitors are one of the richest sources of such molecules, including the common, broad-spectrum drug streptomycin.

Umbrella Toxins: A New Class of Bacterial Weapons

What sets these newly discovered antibacterial toxins apart is that, unlike the small-molecule antibiotics produced by Streptomyces, umbrella toxins are large complexes made up of multiple proteins. They are also much more specific in the bacteria they target. The authors of the Nature paper think that these properties of umbrella toxins explain why they have gone unnoticed for more than a century of research on toxins produced by Streptomyces.

Targeting Their Own Kind: Specificity of Umbrella Toxins

The scientists then tried to figure out the targets of these toxins by testing their effects on every organism they could possibly target, from fungi to 140 different bacteria. Among these potential adversaries, the toxins specifically targeted their own kind: other Streptomyces species. “We think this exquisite specificity may be due to the proteins that make up the spokes of the umbrella, which vary across the particles. These include proteins that might latch onto specific sugars found on the surface of competitor bacteria,” commented study author S. Brook Peterson, a senior scientist in the Mougous lab.

Potential Clinical Applications for Combating Drug-Resistant Bacteria

In addition to the many questions still to be answered about the basic biology of umbrella toxin particles, Mougous and his colleagues are intrigued by their potential clinical applications. They suspect that the bacteria that cause tuberculosis and diphtheria may be sensitive to umbrella toxins, even though these same bacteria have become resistant to traditional antibiotics. The scientists suggested that umbrella toxin particles might be worth exploring for their potential to subdue these serious disease-causing bacteria.