Genetic Variation in Janthinobacterium lividum; An Examination of the Violacein Operon

Probiotic therapeutics are revolutionizing the way we conceptualize and approach the management of pathogens in our environment, from hospitals and households to remote tropical rainforests. Janthinobacterium lividum is an excellent candidate for probiotic use because it produces violacein, a metabolite that destroys or inhibits many types of microorganisms, including bacteria, fungi, protozoans and nematodes, while being nonpathogenic to humans and other vertebrates. Researchers are exploring probiotic treatments based on the antibiotic metabolites produced by live strains of the bacterium in vitro, yet little is known about the broader phylogeny or regional variation of the organism in vivo. Here we examine the variability of the violacein gene coding region in Janthinobacterium species across geographic space and different environmental sources. Sixteen regional strains of the bacterium were included in this study, isolated from environmental sources, such as soil and water, and from the microbiome of living organisms, including amphibians. Genomic analysis focused on the five genes responsible for the production of violacein, along with the 16S rRNA gene, a commonly used bacterial marker gene. Phylogenetically, the violacein operon was more informative than the 16S rRNA gene for determining evolutionary relationships between strains. This operon may be the best choice for classifying violacein- producing bacteria at the species level, short of full genome assembly and analysis. This data set revealed no detectable correlation between environmental source and genotype (e.g. amphibian vs soil or water). A regional pattern was observed at the continental scale