Microbial Community Structure of Submerged Aquatic Vegetation in the Potomac River

Abstract

Background

Submerged aquatic vegetation (SAV) are plants that are rooted in sediment and fully submerged most of the time, and have many adaptations for coping with varied salinity and osmotic conditions. We focus here on one aspect of SAV - their microbiome - which was studied in the Potomac River along a salinity gradient as the river empties into the Chesapeake Bay. The goal was to find a link between the microbial communities on different SAV species and the changing salinity across the river.

Results

One of the four successfully sampled sites was very different from the rest in terms of microbial community and water/sediment chemistry, clustering separately from the other sites on PCoA plots. Methylotenera, Planctomyces, Rhodobacter, and Providencia are commonly found amongst most SAV species across all sites, and sulfur oxidizing bacteria were present in high relative abundance in the roots of Potamogeton perfoliatus at one site.

Conclusions

Site location, which had distinct water and sediment chemistries, was a main driver of the microbial community structure. Host species of SAV and sample types (leaves or roots) also have different microbial communities. Due to the small sample size in this study, it is difficult to draw robust conclusions about the impact of salinity on microbial community structure. Therefore, future efforts will sample more thoroughly along the Potomac river, as well as along the length of the James River, which provides a nearby, parallel salinity gradient.

Background

Salinity is an important factor in determining the distribution of aquatic organisms. Nevertheless, there are some species adapted to a wide range of osmotic conditions, including fish (Whitehead 2011), insects (Pallarés 2015), and plants (Garrote-Moreno 2014). Submerged aquatic vegetation (SAV) are plants that are rooted in the sediment and remain fully submerged most of the time. They are a polyphyletic assemblage restricted to shallow waters by light penetration. They posses several, convergent adaptations to life underwater, including the loss of a waxy cuticle, air cells that allow leaves to float, and specialized epidermal osmoregulartory cells