Pamela Ronald on breaking bacteria’s code

Researchers have deciphered a new chemical code that disease-carrying bacteria use to rally themselves. They call it Ax21.

Good news in the war on germs. Researchers have deciphered a new chemical code that disease-carrying bacteria use to rally themselves. They call it Ax21, a protein made inside the bacterial cell, processed to generate a signal and then secreted outside the bacterium. The knowledge that bacteria use Ax21 to communicate is expected to lead to new methods of controlling bacterial diseases of plants and animals. EarthSky’s Jorge Salazar spoke to plant scientist Pamela Ronald of University of California, Davis, who led the study.

You’ve compared the bacteria using this newly found code to people using the social media service Twitter. What are bacteria tweeting?

Bacteria are tweeting their location and their intent for group action.

The signals that the bacteria secrete are somewhat like hashtags that people will put on their Twitter communications, so that other people who are interested in taking the same action – who have the same target – can congregate together and more efficiently carry out that action. And it allows an action to occur from a group that could not have possibly happen by an individual alone.

Pamela Ronald studies the way bacteria communicate with each other.

So bacteria send out these signals. It’s sort of like enemy communication that allows them to mobilize group action. And when there are enough signals, that means that there are enough bacteria to completely change from benign organisms to being fierce invaders. They will then be able to coordinate attacks on their targets.

What are their targets?

They could be plants, animals and even humans that can become very susceptible to these bacterial infections.

The particular disease that we looked at infects rice crops. It can cause a 50 percent reduction in yield.

The hope is that now that we understand the strategy, with which these bacteria can communicate, we can develop methods to really disrupt their infection process.

How does this research compare to that done by Bruce Beutler and Jules Hoffman, who won the Noble Prize in 2011 in medicine and physiology for similar work with immune receptors?

It’s a really exciting time in plant and animal immunology. Most plants are virtually defenseless when these bacteria attack them, using this coordinated communication. The exception are those plants that carry an immune receptor that can intercept the message produced by the invading microbe. This receptor is called XA21. It belongs to a very large class of immune receptors that are found in both plants and animals.

Salmonella bacteria. Image Credit: NIH

The importance of these receptors is reflected by the Noble Prizes received by professors Bruce Beutler and Jules Hoffman. They discovered these type of receptors in flies and mice.

We know now that in plants and in higher animals, these immune receptors detect some components of microbes that are highly conserved. And so once the plant or animal detects these, it can then launch an immune response are highly conserved. And so once the plant or animal detects these, it can then launch an immune response.

What’s the most important thing you want people today to know about bacteria that signal each other?

I think it’s very interesting for people to know that bacteria can talk to each other. Plants and animals can intercept this coded communication, and then use that information to trigger their own response.

Jorge Salazar

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