Bacteria take aim using toxic darts

UC SANTA BARBARA (US) — Bacteria use stick-like proteins on their surfaces with toxic dart tips to disable their competition, according to new research.

“The discovery of toxic darts could eventually lead to new ways to control disease-causing pathogens,” says Stephanie K. Aoki, first author and postdoctoral fellow in the department of molecular, cellular, and developmental biology at the University of California, Santa Barbara.

“This is important because resistance to antibiotics is on the rise.”

Details appear in the journal Nature.

“First we need to learn the rules of this bacterial combat. It turns out that there are many ways to kill your neighbors; bacteria carry a wide range of toxic darts,” says second author Elie J. Diner, graduate student in biomolecular sciences and engineering.

The darts are delivered to competing neighbor cells when the bacteria touch, a process called “contact dependent growth inhibition,” or CDI.

Some targets have a biological shield. Bacteria protected by an immunity protein called “contact dependent growth inhibition immunity.” can resist the enemy’s disabling toxic darts.

General CDI illustration_525

Illustration of contact dependent growth inhibition (CDI). (Credit: Stephanie Aoki)

Researchers discovered a wide variety of potential toxic-tip proteins carried by bacteria cells—nearly 50 distinct types have been identified so far, says Christopher Hayes, co-author and associate professor of molecular, cellular, and developmental biology.

Each bacterial cell must also have immunity to its own toxic dart. Otherwise, carrying the ammunition would cause cell suicide.

Surprisingly, when a bacterial cell is attacked—and has no immunity protein—it may not die but often ceases to grow.

Similarly, many antibiotics do not kill bacteria; they only prevent the bacteria from growing. Then the body flushes out the dormant cells.

Some toxic tips appear to function inside the targeted bacteria by cutting up enemy RNA so the cell can no longer synthesize protein and grow. Other toxic tips operate by cutting up enemy DNA, which prevents replication of the cell.

“Our data indicate that CDI systems are also present in a broad range of bacteria, including important plant and animal pathogens such as E. coli which causes urinary tract infections, and Yersinia species, including the causative agent of plague,” says senior author David Low, professor of molecular, cellular, and developmental biology.

“Bacteria may be using these systems to compete with one another in the soil, on plants, and in animals. It’s an amazingly diverse world.”

The team studied the bacteria responsible for soft rot in potatoes, called Dickeya dadantii. This bacteria also invades chicory leaves, chrisanthemums, and other vegetables and plants.

Funding for this research came from the National Science Foundation and the National Institutes of Health. The TriCounty Blood Bank also provided funding.

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