Metagenomic deep sequencing reveals association of microbiome signature with functional biases in bovine mastitis.

Milk microbiomes significantly influence the pathophysiology of bovine mastitis. To assess the association between microbiome diversity and bovine mastitis, we compared the microbiome of clinical mastitis (CM, n = 14) and healthy (H, n = 7) milk samples through deep whole metagenome sequencing (WMS). A total of 483.38 million reads generated from both metagenomes were analyzed through PathoScope (PS) and MG-RAST (MR), and mapped to 380 bacterial, 56 archaeal, and 39 viral genomes. We observed distinct shifts and differences in abundance between the microbiome of CM and H milk in phyla Proteobacteria, Bacteroidetes, Firmicutes and Actinobacteria with an inclusion of 68.04% previously unreported and/or opportunistic strains in CM milk. PS identified 363 and 146 bacterial strains in CM and H milk samples respectively, and MR detected 356 and 251 bacterial genera respectively. Of the identified taxa, 29.51% of strains and 63.80% of genera were shared between both metagenomes. Additionally, 14 archaeal and 14 viral genera were found to be solely associated with CM. Functional annotation of metagenomic sequences identified several metabolic pathways related to bacterial colonization, proliferation, chemotaxis and invasion, immune-diseases, oxidative stress, regulation and cell signaling, phage and prophases, antibiotic and heavy metal resistance that might be associated with CM. Our WMS study provides conclusive data on milk microbiome diversity associated with bovine CM and its role in udder health.