Short-Term Effects of Critical Metal Concentrations on Usnic Acid Production in Cladonia rangiferina

Abstract

Cladonia rangiferina is a lichen that produces usnic acid, a selectively toxic biomolecule, allowing the lichen to protect itself from predators and regulate populations of microorganisms, other fungi, and animals in its vicinity. Unfortunately, metal pollution associated with human industrial activity has hindered C. rangiferina’s metabolism, as indicated by its decreasing population in areas with high metal concentrations. It was unclear whether C. rangiferina’s ability to produce usnic acid was also hindered in polluted environments and whether the type of metal pollutant led to different effects. A short-term experimental study was used to isolate the effects of concentrated copper, nickel, and zinc ions on this metabolic pathway. It was found that nickel (+2) does not significantly affect usnic acid production, whereas even small concentrations of copper (+2) dramatically reduce it. Meanwhile, the concentration of zinc (+2) seems to be negatively correlated with usnic acid production in the short term. This means that priority regions for C. rangiferina population restoration projects include areas with critically high concentrations of copper and zinc, but not nickel. Further research is needed to a) explain how usnic acid synthesis changed rapidly under varying copper conditions compared to zinc and b) identify changes to this molecule’s synthesis under a combination of metal stresses. This study could clarify the metabolic pathway of usnic acid production and refine plans for artificial dispersal (a lichen conservation method).