Gut fungi: Unexpected source of novel chemicals

Anaerobic fungi, which die in the presence of oxygen, dwell in herbivore guts and help them digest their last leafy meal. In their evolutionary history, these fungi branched off early from aerobic fungi, which can breathe oxygen – just like we do.

Oxygen is a rich source of energy, and because anaerobic fungi can't harness it, scientists long held that these fungi don't have the energy to make complex compounds called natural products. Yet, combing through the genomes of four anaerobic fungal species has revealed, for the first time, that this group is unexpectedly powerful: they can whip up dozens of complex natural products, including new ones.

A team led by Michelle O'Malley, a chemical engineer at the University of California (UC), Santa Barbara, collected the droppings of a sheep and a goat at the Santa Barbara Zoo, and those of a horse in Massachusetts, in their hunt for anaerobic fungi. By growing extracts without oxygen in ruminant fluid – which smells terrible – they were able to isolate four strains: Anaeromyces robustus, Caecomyces churrovis, Neocallimastix californiae, and Piromyces finnis.

In the past, natural products have been an important source of antibiotics. Indeed, these anaerobic fungi may be using these compounds for self-defense. But the compounds may also be involved in how the fungi metabolize plant biomass, which could inform how scientists can more easily convert plants into carbon-neutral biofuels.

What's more, many natural products have potential to be used as precursors for polymers and commodity chemicals, as well as drop-in biofuels. This work shows that anaerobic fungi might be a new source of novel compounds to help bolster the bioeconomy.