Biologists at UCSB have published a study in the journal Nature that found that certain bacteria fight for evolutionary dominance using “toxic darts” to attack and disable their competitors.

According to first author and postdoctoral fellow of molecular, cellular and developmental biology Stephanie K. Aoki, the “darts” are long proteins with a sharp end that pierces surrounding bacteria and injects them with a toxic compound that attacks their ability to grow and reproduce. This process is known as “contact dependent growth inhibition,” or CDI.

[media-credit name=”PHOTO COURTESY OF Stephanie K. Aoki” align=”alignleft” width=”148″][/media-credit]

A diagram describing contact-dependant growth inhibition in protected and vulnerable bacteria.

“The idea is that when you mix the two bacteria together they touch, and upon contacting each other the very end of the toxic dart protein (on the inhibitor cell) transfers into the target cell, resulting in growth inhibition of the target,” Aoki said in an e-mail.

The toxic darts, rather than killing the bacteria, prevent it from reproducing or growing by breaking down RNA strands, which are required to synthesize new proteins.

The bacteria do not target themselves or other bacteria that use the toxin, helping to secure a place in the microbial pecking order by allowing their genetic counterparts to proliferate among their stagnant rivals.

“If the target cell contains the matching immunity protein … [the bacteria] will be protected from inhibition,” Aoki said. “Inhibitor cells that have the toxic protein always have an immunity protein — if they didn’t have an immunity protein they would not be protected from themselves and would auto-inhibit.”

Aoki said the study may be used to find ways to control microorganisms that cause disease.

“The discovery of toxic darts could eventually lead to new ways to control disease-causing pathogens,” Aoki said in a press release. “This is important because resistance to antibiotics is on the rise.”

Aoki worked with biomolecular sciences and engineering graduate student and second author Elie J. Diner, as well as associate biology professor Christopher Hayes and biology professor David Low to produce the research.

Low said the study has found many forms of the toxic darts within bacteria.

“Our data indicate that CDI systems are also present in a broad range of bacteria, including important plant and animal pathogens,” Low said in a press release. “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.”

In the future, Aoki said the researchers will continue to look into the various kinds of toxic darts.

“We’ve just scratched the surface — we don’t know how many types of toxic tips there are, as there seem to be many bacterial species out there with this system … In a plant pathogen, this system is useful for competing against other bacteria on a plant,” Aoki said. “We still do not know if this system gives an advantage to other bacteria in different environments. We are also trying to understand how the toxic tips get into target cells. Although we still have a long way to go, perhaps an understanding of this system will eventually lead to the development of new antimicrobial therapies.”