Conflict under control

eLife publication shows fungal secondary metabolite is regulated by environment.

In his PhD Markus Greßler studied the substance Terrein from the mold Aspergillus terreus. (Photo: HKI/Anna Schroll)

Seldom understood are the ecological and physiological roles of fungal secondary metabolites. Like any organism, the goal of the fungus Aspergillus terreus is to survive; A. terreus has suitably evolved a helpful tool, the small molecule terrein. Scientists from the HKI have studied the competitive advantage conferred to A. terreus by terrein, and their results have now been published in the scientific journal, eLife.

Matthias Brock and Markus Greßler at the Leibniz Institute for Natural Product Research and Infection Biology – Hans-Knöll Institute set out to study the pigmentation of the fungus Aspergillus terreus. During this work, they serendipitously discovered the gene cluster responsible for terrein production. Terrein is the major secondary metabolite produced by A. terreus, yet it’s ecological relevance was unknown; Matthias Brock, group leader at the HKI until March 2015 and now a professor at the University of Nottingham, says “We asked ourselves: Why is the fungus wasting these resources?”

The brown spots on the banana peel are caused by Terrein (line WT, ΔakuB). If the responsible genes are destroyed, no Terrein can be formed and the browning does not occur (ΔterA, ΔterR). (Source: eLife)

Far from being wasted, terrein confers a competitive advantage to Aspergillus terreus. In particular, it reduces competition by attacking the cells of fruits, roots, and seeds, as well as possessing moderate antifungal activity, and supporting growth of A. terreus under iron starvation. Significantly, the fungus is able to sense its environment and regulate the production of terrein. Three independent environmental signals were found to be regulators: the absence of nitrogen, the absence of iron, and the presence of the amino acid, methionine. These factors signal the surrounding plant and rhizosphere environment, increasing terrein production in times of greater competition for resources.

Brock and Greßler, among others, required creative methods to study the factors affecting terrein production; Matthias Brock says, “There were days when my colleague, Markus Greßler, brought shopping bags full of various fruits and fruit juices to the laboratory. They were used to test how the fungus reacts to fruit.” Besides terrein, Aspergillus terreus also produces other substances of interest, for example lovastatin, a drug used clinically to lower cholesterol.

(Tina Kunath, translation: Robert Barnett)