Investigating the Functions of the Plant-associated Genus Variovorax in the Populus Rhizosphere

Plants host a diverse microbial community living in close association with their roots (rhizosphere) or inside plant tissues (endosphere) that can form beneficial, pathogenic, or neutral relationships. Understanding these relationships can inform strategies for manipulating the microbiome of plants to promote plant growth and productivity. Among the microbes isolated and sequenced from the Populus rhizosphere and endosphere are a number of Variovorax isolates. Variovorax ssp. are motile, Gram-negative bacteria that belong to the family Comamonadaceae and are known for their diverse metabolism. For this work, we characterized thirteen new Populus-associated Variovorax strains, twelve of which were isolated from the endosphere and one from the rhizosphere of Populus. Genomic comparisons indicate that these isolates encode a high level of genomic and metabolic diversity. We have performed assays to characterize interactions between Variovorax and other bacterial strains, examined biosurfactant production, and performed genome analyses to predict biosynthetic gene clusters for natural product production by the Variovorax species. Despite being isolated from a common host, these analyses indicate that the Populus-associated Variovorax strains show variations in metabolic potential, in their interactions, in the diversity and abundance of biosynthetic gene clusters, and in biosurfactant production.