Secondary Metabolites in Cheese Fungi

Several filamentous fungi grow on the surface or inside different types of cheese, produce secondary metabolites, and contribute to the organoleptic characteristics of mature cheese. Particularly relevant is the contribution of Penicillium roqueforti to the maturation of blue-veined cheeses (Roquefort, Danablu, Cabrales, etc.). P. roqueforti is inoculated into these cheeses as a secondary starter. This fungus is closely related taxonomically to Penicillium carneum and Penicillium paneum, but these two species are not used as starters because they produce the potent toxin patulin. P. roqueforti Thom has the capability to produce about 20 secondary metabolites of at least seven different families, but it seems that only some of them are produced in microaerobic conditions and accumulate inside the cheese (e.g., andrastins). This article focuses on the biosynthetic pathways, gene clusters, and relevance of the known metabolites of P. roqueforti including roquefortines, PR-toxin and eremofortins, andrastins, mycophenolic acid, clavines (agroclavine and festuclavine), citreoisocoumarin, and orsellinic acid. In addition the biosynthesis of patulin (a P. paneum and P. carneum product) is discussed. Penicillium camemberti grows on the surface of Camembert, Brie, and related white rind cheeses, and the penetration of secondary metabolites inside the cheese is relevant. One of the P. camemberti metabolites, cyclopiazonic acid, is important because of its neurotoxicity and its biosynthesis is reviewed. The removal of toxic metabolites gene clusters by precise gene excision while preserving all other characteristics of the improved starter strains, including enzymes involved in cheese ripening and aroma formation, is now open. A possible strain improvement application to the cheese industry is of great interest.