Nutrient-Dependent Plant Driven Colonization Patterns

Recent studies from the Earth Microbiome Project have shown that in moving from the rhizosphere to the surface or inside of the plant, the microbial diversity plummets (Thompson et al, 2017). While few in number the microbes that are able to live in close association with the plant, endophytes or strongly adherent epiphytes, have been shown to be widely culturable (Bai et al, 2015). Small synthetic communities in an environment that is both highly selective and easily cultured can then provide scientists a way to study the interactions between a host and it's colonizers. We created a synthetic community from isolates of the agriculturally relevant plant Medicago sativa and screened for physiological traits relating to plant growth promotion such as phosphate and potassium solubilization. Using drop out communities, where each community member is removed one at a time to determine its role in community structure, we identify two members who have large roles in overall community structure; Pantoea sp. R4 and Williamsia sp. R60. Within the drop out communities, we modulate nitrogen levels and uncover microbial structure changes that only occur within the presence of the plant and ones that are dependent on changes in nitrogen.