White hat fungus fights off pathogens

TEXAS A&M (US) — A fungus that already has a good reputation is making a name for itself as a therapeutic agent for human and plant health.

Because they are mycoparasites, Trichoderma virens are able to attack other, less desirable fungi that can harm roots and foliage of plants.

Colonization of plant roots by T. virens also prompts the plant to produce defense responses to fight off pathogenic fungi.

As a bonus, when no pathogens are loitering, T. virens enhance the growth of plants.

“We started working with this organism because it has what we would call biological control activity,” says Charles Kenerley, research plant pathologist at Texas A&M University. “They are used either as seed treatment, as a foliar spray, or in the mixtures of potting soil at nurseries (to help control disease).”

The research by an international group of scientists is reported in the Journal of Biological Chemistry.

“These fungi are very diversified organisms that have various roles in ecology,” Kenerley says, “so agriculture has adopted them for use in biocontrol or growth promotion.

“T. virens will colonize most agricultural crops including corn, cotton, sorghum, and alfalfa, as well as woody plants and numerous other nursery plants.”

Anything good enough to fight off disease and encourage growth might have more to offer, so scientists looked deeper and found that T. virens also produce antibiotics and short chains of amino acids called peptaibols.

Because they string together to form protein, amino acids are like the cinder blocks of all living things, Kenerley says.

In the new study, researchers found two classes of peptaibols that contain more than 70 components that had never been described.

“What is also exciting is that the 11- and 14-amino acid peptaibols have great diversity, Kenerley says. “The chemists I work with have been able to identify 52 different forms of  this 11-amino acid peptaibol. When you have so many different forms, you have now a suite of compounds that you can test  (for potential uses).”

Sorting out that diversity to determine any specific uses for each of the 52 forms is something the team continues to pursue.

“Some might be interesting for use in plant science and some might be looked at by the pharmaceutical industry for human uses,” he says.

“The biggest challenge is not only in selection of the most appropriate form, but then how do you gear the organism to produce more of what you want rather than the whole suite of its compounds.”

“There’s probably an ecological reason the fungus produces a diversity of these compounds. I’m sure it has to do with survival in the soil, and its interaction with other organisms and plant roots. The compounds are not necessarily there for our benefit, but we would like to use these compounds in different applications,” he adds.

While Kenerley’s team is considering agricultural uses for the peptaibols, others are considering pharmaceutical uses for treating tumors in humans or perhaps their ability to work against harmful bacteria, fungi and viruses.

“You can see that they would have great potential if they have therapeutic value but are not harmful to the hosts—the hosts being humans,” Kenerley adds.

Once researchers understand how the peptaibols are produced by the fungus, the fungus could be potentially modified to produce only the part needed for a specific use.

“If we can demonstrate a cheap way to make these, the specific form desired could be synthesized,” Kenerley says.

“The problem right now is there are so many forms of these peptaibols, you really don’t know which one to go after. We need to figure out ‘do I need a combination of these things?’ or really do I only need to make one or two?”

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