Nematode-Trapping Fungus Arthrobotrys oligospora is Hungry for COQ7 to Alleviate Environmentally Triggered Iron Overload

Abstract

Choosing the right and appropriate amount of substances in a changing environment is essential for the growth and survival of all species. We found that elevated oxygen levels significantly enhanced the iron-rich trapping devices of a nematode-trapping fungus (NTF), Arthrobotrys oligospora. Interestingly, genomic analysis revealed that all NTFs lacked coq7, a key gene involved in ubiquinol (UQ) biosynthesis and iron chelation. Notably, A. oligospora utilizes UQ instead of UQ for low-aerobic respiration. Transcriptional, metabolic, mutational, and phenotypic analyses revealed that A. oligospora produces a chemotaxonomic class of highly oxygenated arthrobotrins with characteristics similar to UQ skeleton, for high-aerobic respiration. Disruption of arthrobotrin biosynthesis in the {Delta}art mutant not only enhanced UQ biosynthesis, but also triggered trapping device formation and nematicidal activity under elevated oxygen conditions. The addition of UQ to both wild-type and {Delta}art mutants strongly inhibited trapping device development. Remarkably, the iron-rich trapping devices preferentially capture N2 nematodes harboring iron-chelating COQ7 with ferritin properties. Time-calibrated evolutionary analyses, combined with geological data, indicated that the NTF ancestor lost the coq7 gene after acquiring the arthrobotrin biosynthetic gene cluster during the "superoligotrophy" period, characterized by dramatic shifts in global oxygen levels and temperature changes. Our results demonstrate that oxygen is a critical factor in inducing iron overload, highlighting the origin and role of coq7 loss in the evolution of predatory behavior of NTFs. Our finding that NTFs capture nematodes for iron chelation therapy, rather than for food, explains a long standing debate about the limited carnivorous ability of trapping devices.