Taming wild mould to make new cheese flavours

Industrial cultures of filamentous fungi are used to add unique aesthetics and flavours to cheeses and other microbial foods. Fermented foods are hybrid microbiomes where wild microbial species from the environment mix with domesticated microbes that are added as starter cultures.

The flavours of fermented foods are heavily shaped by the fungi that grow on them, but the evolutionary origins of those fungi aren’t well understood. Experimental findings published in mBio provide a new view on how those moulds evolve from wild strains into the domesticated ones used in food production.

According to study leader and microbiologist Dr Benjamin Wolfe, PhD, the research paper reports that in a matter a matter of weeks, wild-type Penicillium moulds resembled their domesticated cousin, Penicillium camemberti, the mould that gives camembert cheese its distinctive flavour. The work suggests that some wild strains could evolve quickly to produce new flavours and aesthetics in fermented foods.

Wolfe’s lab at Tufts University focuses on microbial diversity in fermented foods, but he said the new experiments began with an accidental discovery. His lab had been growing and studying Penicillium commune, a bluish, wild-type fungus well known for spoiling cheese and other foods. Wolfe likens its smell to a damp basement.

But over time, researchers noticed changes in some of the lab dishes containing the stinky mould. “Over a very short time, that funky, blue, musty-smelling fungus stopped making toxins,” Wolfe said. The cultures lost their bluish hue and turned white; they smelled like fresh grass and began to look more like P. camemberti. “That suggested it could really change quickly in some environments,” he said.

To study that evolution in real time, Wolfe and his collaborators collected fungal samples from a cheese cave in Vermont that had been colonised by wild strains of Penicillium moulds. The researchers grew the moulds in lab dishes containing cheese curds. In some dishes, the wild mould was grown alone; in others, it was grown alongside microbes that are known competitors in the fierce world of cheese colonisation.

After one week, Wolfe said, the moulds appeared blue-green and fuzzy — virtually unchanged — in all the experimental tests. But over time, in the dishes where the mould grew alone, its appearance changed. Within three or four weeks of serial passage, during which mould populations were transferred to new dishes containing cheese curds, 30–40% of the mould samples began to look more like P. camemberti. In some dishes, it grew whiter and smoother; in others, less fuzzy. (In the competitive test cases, the wild mould did not evolve as quickly or noticeably.)

In follow-up analyses, Wolfe and his team tried to identify genomic mutations that might explain the quick evolution but didn’t find any obvious culprits. “It’s not necessarily just genetic,” Wolfe said. “There’s something about growing in this cheese environment that likely flips an epigenetic switch. We don’t know what triggers it, and we don’t know how stable it is.”

Researchers suspect that the microbes used in most fermented foods — including cheese, but also beer, wine, sake and others — were unintentionally domesticated, and that they evolved different flavours and textures in reaction to growing in a food environment. Wolfe said his lab’s study suggests that wild strains could be domesticated intentionally to produce new kinds of artisanal foods.

Starting with cheese, of course. “The fungi that are used to make American camembert are French,” Wolfe said, “but maybe we can go out and find wild strains, bring them into the lab and domesticate them. We could have a diverse new approach to making cheese in the United States.”

mBio is published by the American Society for Microbiology.

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