Metagenomic analysis of a Mexican ripened cheese reveals a unique complex microbiota.

Cotija cheese is a Mexican handcrafted product made from raw cow milk whose ripening process occurs spontaneously and, presumably, it is influenced by environmental conditions. Its sensory characteristics and safety are probably the result of the balance between microbial populations and their metabolic capacity. In this work, we studied the dominance and richness of the bacteria in the Cotija cheese microbiome, as well as their metabolic potential by high-throughput sequencing. By the analysis of 16S ribosomal sequences, it was found that this metagenome is composed mainly of three dominant genera: Lactobacillus, Leuconostoc and Weissella, and more than 500 of non-dominant genera grouped in 31 phyla of both bacteria and archaea. The analysis of single-copy marker genes reported a similar result for dominant genera, although with greater resolution that reached the species level. Pathogenic bacteria such as Salmonella, Listeria monocytogenes, Brucella or Mycobacterium were not found. The Cotija cheese microbiome has the metabolic capacity for the synthesis of a wide range of flavor compounds, mainly involved with the metabolism of branched chain amino acids and free fatty acids. Genes associated with bacteriocin production and immunity were also found. Arguably, this is one of the most diverse metagenomes among the microbial communities related to fermented products.