For some scientists, there’s no place more romantic than a cheese cave. When Tufts University biologist Benjamin Wolfe, then a biology postdoc, shepherded his colleague Rachel to a surprise rendezvous with her boyfriend in a Vermont cheese cave, a marriage proposal ensued. And, according to Wolfe and his colleagues’ new paper in Current Biology, so did a discovery about evolution.
Some cheese varieties are ripened in caves where they attract microbes—yeast, bacteria, and fungi (molds)—which form a rind on the cheese surface. Molds like Penicillium (the same genus that produces the human antibiotic, but a different species) spur the ripening of the cheese. P. roqueforti, for example, gets blue cheese started, while P. candidum confers a soft, creamy texture.
Some molds are beneficial, while others can ruin the cheese, so aging cheeses is a delicate balance between cultivating and culling the molds.
Read more: “The Man Who Blamed Aging on His Intestines”
Wolfe was intrigued by the scene surrounding the marriage proposal in that Vermont cheese cave, and he took samples of Bayley Hazen Blue cheese back to his lab and froze them, for years. At the time, he noted the mottled greenish brown microbial rind on the cheese, which he analyzed, realizing it consisted mostly of a filamentous fungus, Penicillium solitum.
But when he sent his grad student, Nicholas Louw, to get new samples from the farm years later, the cheese rinds were totally white.
“This was really exciting because we thought it could be an example of evolution happening right before our eyes,” said Wolfe, now a microbiologist at Tufts University, in a statement. The cheese-making process had not changed, nor had the environment in the caves, suggesting that the microbes had evolved on their own, reacting to some unseen selection pressure.
When Louw, Wolfe, and colleagues analyzed the new composition of microbes in the cheese rind, they discovered a genetic explanation for the color change. A disruption in a gene, alb1, which plays a role in melanin production, had changed the rind from greenish brown to white. The researchers surmise that, in the dark environment of the cave, melanin was no longer necessary for protection from sunlight. So, in an example of “relaxed selection,” the pathway for melanin production was genetically silenced.
“By breaking that pathway and going from green to white, the fungi are essentially saving energy to invest in other things for survival and growth,” added Wolfe.
Witnessing mold evolution may not spark further instances of romance, but it is likely to inform the cheese-making process through intentional cultivation and selection for microbial communities that could yield new flavors of cheese. 
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