Microbial ecosystems from ripened cheeses - Compositions and functions

Cheeses are highly prized products throughout the world. Their organoleptic properties are developed through the use of a variety of cheese-making technologies, all of which involve coagulation of the milk, draining of the curds, salting and ripening, generally at low temperatures. It is mainly during this last stage that a microbial community develops on the curds, the structure and composition of which vary according to the technology, thus generating a diversity of microbial ecosystems.

As in any ecosystem, the cheese microbial ecosystem or cheese microbiota is the result of a complex interaction between the physico-chemical environment (curd substrates, humidity, atmospheric composition, temperature, pH, etc.) and the micro-organisms growing in or on the cheese curd.

As with many traditional fermented products, recent data show that the microbiological complexity of cheeses is far greater than was imagined in the 20th century. Progress has been made not only in describing the biodiversity of this microflora, but also in the origins of the species that make up the ecosystem, the physico-chemical selection factors that lead to the multiplication of specific populations, and finally the functioning of these ecosystems in terms of biological interactions. The latter can be positive, neutral or negative. For several decades, most research has focused on lactic acid bacteria, important above all in fresh dairy products, while recent knowledge has focused more on refining flora, which appear to be much more diverse from a taxonomic and functional point of view.

This microbiota develops a set of properties that will make cheeses healthy and safe products, giving them resistance to contamination by spoilage agents or, more seriously and unacceptably, contamination by pathogenic bacteria. In addition, the physiological properties of the agents making up the ecosystem, combined with the characteristics triggered by cheese-making technologies, generate specific organoleptic characteristics and lead to the diversity of colors, textures, flavors and aromas we enjoy on our cheese boards.

Molecular approaches implemented over the last twenty years, and the more recent development of genomic techniques based on high-throughput sequencing, have enabled considerable progress to be made in these areas. Genomics (species-by-species analysis of DNA sequences) and metagenomics (sequencing all the DNA sequences in a cheese) have enabled us to assess the diversity of micro-organisms found in this biotope, as well as their potential:

• adaptation to dairy substrates and to the constraints imposed by the cheese-making technologies used;

• by their biological...