French cheese under threat

01.16.2024, by

Cheeses host a multitude of microorganisms that turn milk into curds. Selected by humans, these ferments are not exempt from food industry regulations – to the point that blue cheeses and Camembert could disappear.

Ever heard of Termignon blue? This little-known cheese, produced by just a few farms in the French Alps, could well save the entire blue cheese industry, which is threatened with extinction due to the standardisation of production processes. This is because its characteristic blue-green mould comes from a previously unknown population of Penicillium roqueforti, the fungus used in the fermentation of all blue and veined cheeses. The discovery is a bombshell in the world of cheese.

Termignon blue, made in the Savoie region in the French Alps, naturally develops a blue-green mould, unlike other blue cheeses that are inoculated with “Penicillium”.

“Until now, only four populations of the P. roqueforti species were known in the world,” reports Jeanne Ropars, who, with Tatiana Giraud and their team at the ESE1 in Gif-sur-Yvette (near Paris), has successfully sequenced the genome of the microorganism responsible for the fermentation of Termignon blue.

This consists in “two ‘wild’ populations, involved in the rotting of fruit, the decomposition of certain foods and silage (the fermentation of fodder for livestock - Editor's note), plus another two used in cheese production”, the researcher specifies. Of the two domesticated populations, one is specifically dedicated to PDO (Protected Designation of Origin) Roquefort, whereas all the other blue cheeses are inoculated with a single strain of P. roqueforti.

To produce cheese in large quantities, manufacturers have selected fungus strains that meet their self-imposed specifications. The cheeses must be appealing, with a good flavour, no unappetising colours and no mycotoxins (toxins secreted by fungi), and the chosen fungus must grow quickly in the cheese that it is intended to colonise. In pursuit of this goal, the food industry has exerted so much pressure on the selection of fungi that the microbial diversity among non-farm-produced, non-PDO cheeses has become extremely impoverished.

Blues entering the red zone

“We’ve been able to domesticate these invisible organisms just as we did with dogs or cabbage,” Ropars explains. “But what happened, as it does every time an organism large or small is subjected to overly drastic selection, is that their genetic diversity has been greatly reduced. Working with microorganisms, the cheese makers didn’t realise that they had selected a single individual, which is not sustainable over the long term.” Microorganisms are capable of both sexual and asexual reproduction, but the industry relied primarily on the asexual method, producing clonal lineages to perpetuate the moulds. As a result, they can no longer reproduce with other strains that could provide them with new genetic material, a situation that, over time, induces the degeneration of the strain in question.

A 3D illustration of the “Penicillium roqueforti” fungus used in the production of blue cheeses.

“The population used in PDO Roquefort has not suffered so much from the selection process, and still has a bit more diversity,” adds Giraud, who reports having identified several different strains. This is not the case for the clonal line used by the rest of the producers, which has been weakened to the point of becoming nearly infertile. “Even the smallest cheese makers are affected,” the researcher recounts. “For a long time they ‘grew’ their own strains of P. roqueforti, but now they mostly buy their ferments directly from large spore producers that supply the entire food industry.”

Consequently, the fungi that have accumulated multiple deleterious mutations in their genomes over years of vegetative propagation become virtually infertile, adversely affecting cheese production. “This is what happens when we completely stop using sexual reproduction,” Giraud explains. “It’s the only way to compensate for detrimental mutations through the introduction of new genes – the famous genetic mixing.”

This is where Termignon blue, with its newly-discovered population of P. roqueforti, comes into play: it could in fact offer cheese producers the genetic diversity that is woefully lacking in their ferments. However, this means assuming the risk of sexual reproduction, which does indeed create diversity but also causes greater variability in the finished product.

Camembert on the endangered list

Blue cheeses may be under threat, but the situation is much worse for Camembert, which is already on the verge of extinction. The world over, this other symbol of French gastronomy is inoculated exclusively with one single strain of Penicillium camemberti, a white mutant that was selected for Brie cheeses in 1898 and Camemberts in 1902.

The problem is that ever since then the strain has been replicated by vegetative propagation only. Until the 1950s, Camemberts still had grey, green or in some cases orange-tinged moulds on their surface. But the industry was not fond of these colours, considering them unappealing, and staked everything on the albino strain of P. camemberti, which is completely white and moreover has a silky texture. This is how Camembert acquired its now-characteristic pure white rind.

Year after year, generation after generation, the albino strain of P. camemberti, which was already incapable of sexual reproduction, lost its ability to produce asexual spores. As a result it is now very difficult for the entire industry to obtain enough P. camemberti spores to inoculate their production of the famous Norman cheese.

The albino strain of “P. camemberti” gives Camembert its characteristic white, silky rind.

Worse still, while the Roquefort PDO standard retains a degree of microbial biodiversity, the PDO specifications for Camembert require farmers and other producers to use P. camemberti exclusively. To compensate for the shortcomings caused by its degeneration, some cheese makers resort to supplementing P. camemberti with a second species of fungi: Geotrichum candidum, also selected for its white, cottony texture.

So what can be done to save Camembert? Should producers return to a “wild” population, similar to P. camemberti, and restart the long process of domestication? Could they resort to genome editing technologies in order to counter the accumulation of mutations or the loss of specific genes with a given desirable function? “People in the industry sometimes ask us whether it’s possible to modify a gene and allow a strain to sporulate in greater quantities,” Giraud reveals, quickly adding that this would not solve the problem: “Genome editing is another form of selection. What we need today is the diversity provided by sexual reproduction between individuals with different genomes.”

Cultures of “Penicillium camemberti” (white and cottony) and “Penicillium biforme” (greyish green) in a petri dish.

A species that is genetically similar to P. camemberti, called Penicillium biforme, also found in cheese because it is naturally present in raw milk, possesses an incredible genetic and phenotypic diversity. This opens up the possibility of inoculating Camemberts and Bries with P. biforme. If cheese lovers want to keep enjoying these products, they will have to learn to appreciate greater diversity in flavour, colour and texture, perhaps even among cheeses from a single source. And, who knows, thereby contribute to enriching our gastronomic heritage. ♦

Footnotes