Genomic analysis of Brucella melitensis reveals new insights into phylogeny and evolutionary divergence.

PURPOSE: Brucellosis is a bacterial zoonotic disease caused by genus Brucella. The disease is often transmitted to humans by direct or indirect contact with infected livestock or from laboratory exposure. In this study two clinical isolates of Brucella melitensis were subjected to whole genome sequencing (WGS) using Ion Torrent PGM and Oxford Nanopore MinIon platform. METHODS: The two hybrid complete genomes were subjected to core gene SNP analysis to identify the relative evolutionary position. To distinguish between the various lineages of B. melitensis, Pangenome analysis was carried out. RESULTS: Phylogenetic analysis revealed that both the study isolates (ST8) clustered along the other Asian isolates that formed genotype II. Genome wide analyses of 326 B melitensis isolates suggests 2171 gene clusters were shared across all the genomes while 3552 gene clusters were considered as accessory genes. CONCLUSION: Here we attempted to provide the gain and loss of six unique genes that defined the phylogenetic lineages and complex evolutionary process. As the severity and prevalence of human brucellosis is increasing a better understanding of Brucella genomics and transmission dynamics is needed.