The aeroponic rhizosphere microbiome: community dynamics in early succession suggest strong selectional forces

In the last decade there has been increased interest in the manipulation of rhizosphere microbial communities in soilless systems (hydroponics) through the addition of plant growth promoting microbes (PGPMs) to increase plant nutrition, lower plant stress response, and control pathogens. This method of crop management requires documenting patterns in communities living in plant roots throughout the growing season to inform decisions on timing of application and composition of the supplemental PGPM consortium. As a contribution to this effort, we measured changes in the bacterial community through early succession (first 26 days) in plant root biofilms growing in an indoor commercial aeroponic system where roots were sprayed with a mist of nutrient-amended water. By 12 days following seed germination, a root-associated community had established that was distinct from the source communities found circulating in the system. Successional patterns in the community over the following 2 weeks (12-26 days) included changes in abundance of bacterial groups that have been documented in published literature as able to utilize plant root exudates, release plant hormones, or augment nutrient availability. Six bacterial families/genera (Hydrogenophilaceae, Rhizobium, Legionellaceae, Methylophilus, Massilia, or Herbaspirillum) were the most abundant in each root sample, comprising 8-37% of the microbiome. Given the absence of soil-associated microbial communities in hydroponic systems, they provide an ideal design for isolating plant-microbial interactions and identifying key components possibly contributing to plant health.