The U.S. National Mall Microbiome: A Census of Rhizosphere Bacteria Inhabiting Landscape Turf

Turf contains living assemblages of not only grass plants but also a plethora of microorganisms that may play critical roles in plant health through interactions such as predation, mutualism, and resource competition.  Little is known about the turf microbiome, and how it might change in response to renovations such as new sod installation or overseeding.  In this work, we survey bacteria inhabiting the rhizosphere of mature and recently renovated turf stands at the United States National Mall in Washington, D.C.  We contrasted these data with the microbiomes of sod soon to be planted at the National Mall, and from the lawn of a nearby government facility.  The soil-inhabiting microbiome was quantified through high-throughput next generation sequencing of the 16S rDNA SSU. 1,657 OTUs were identified from 9.2 million sequence reads, of which 751 could be diagnosed at the genus level.  Over 50% of the 751 identifiable bacterial taxa were members of the phylum Proteobacteria, predominately in the genus Rhodoplanes.  Phenotypic mapping of predicted microbial function based on taxonomy showed all four locations were diverse, and in general contained an abundance of gram-negative, aerobic, free-living thermophilic organisms.  Ordination plots showed clustering of samples according to location.  However, this pattern of differentiation between locations was not recapitulated using hierarchical clustering analysis, alpha diversity measurements, or ANOSIM, with no significant differences between the four locations identified.  Given the commonality of bacterial communities between locations, these data suggest that the resident National Mall microbiome may not experience appreciable change due to the renovation process.