Shotgun Metagenomics of Traditional Bulgarian Green Cheese Reveals Key Roles of <em>Brevibacterium aurantiacum</em> and <em>Aspergillus puulaauensis</em> in the Ripening Process

The distinct sensory properties of artisanal cheeses are defined by unique microbial communities and the key compounds they produce during maturation. Traditional Bulgarian green cheese is only produced in the village of Cherni Vit. To better understand the unique microbial community of this type of cheese, we performed shotgun metagenomic sequencing on a sample of the cheese. We found the dominant microorganisms are various species from the genus Brevibacterium (51%), most notably B. aurantiacum (29%). While having a much lower abundance, the genus Brachybacterium (2%) also plays an important role in ripening. Lactic acid bacteria, specifically Lactobacillus delbrueckii subsp. bulgaricus (19%) and Streptococcus thermophilus (7%) also represented a significant share of the community composition. Functional profiling suggests Brevibacterium is a major producer of amino acids such as Phe, Arg, and Lys, as well as cofactors and vitamins like B5 and B6, and lipoic acid. We found the mold Aspergillus puulaauensis (3%) plays a key role in both lipid and amino acid metabolism within the community, despite its low abundance. No pathogens were present, but genes and plasmids encoding antibiotic resistance were detected at low concentrations. We found green cheese consumption is safe, and could be a source of useful secondary metoblites.