Abstract Detail

Molecular Ecology

Baker, Stokes S. [1], Peeples, Keona [1], Shella, Sameh M. [1], Fijal, Savannah [1], Lopez, Sarah M. [1], Chames, Nicholas M. [1], Kooner, Taj P. [1], Mims, Mitchell A. [1].

Metagenomic Analysis of Giant Duckweed (Spirodela polyrhiza) Microbiota Suggests a Role for Rhizobia in Nutrient Sequestration.

The goal of this investigation is to identify candidate bacterial species that help aquatic plants grow in low-nutrient environments. Giant duckweed (Spirodela polyrhiza) is a free-floating plant that is distributed throughout much of North America. To evaluate S. polyrhiza's growth response in low phosphorus environments, axenic cultures were grown on modified Schenk and Hildebrandt media containing varying concentrations of phosphate. In media containing as much as 500 ?g/L P, only linear increases in frond counts were observed. The plants were chlorotic. Plants were evaluated for their ability to grow in sterile lake water. Plants that were inoculated with duckweed biofilm microbes had a 26% higher growth rate than their axenic counterparts. In another experiment the same S. polyrhiza clone was grown in free-flowing containment cages in Lake Saint Clair (Harrison Township, Michigan, USA), frond number increased exponentially. Additionally, no chlorosis was observed. Chemical analysis of the lake water detected orthophosphate at 7 to 15 ?g/L P. Since retarded growth was detected in the axenic cultures, a microbial role in duckweed nutrient assimilation is suspected. Vital staining with SYTO9/propidium iodide showed rich microbial communities consisting of bacteria and fungi residing on epidermal surfaces of giant duckweed. A metagenomics approach, using the protocols established by the Earth Microbiome Project, was used to identify the bacteria growing on the surface of S. polyrhiza. Amplicon libraries made to Variable Region 4 of 16S rRNA genes were sequenced with an Illumina (San Diego, CA, USA) MiSeq. Results from queries of the SILVA rRNA gene database showed that the duckweed biofilm contained diverse bacterial biota. Shannon diversity indices at the level of the operational taxonomic unity (OTU) had a median value of 3.15 with an interquartile from 2.54 to 3.72. Differential abundance statistical analysis using the Gaussian fit model in metagenonmeSeq showed that members of the Aeromonadales, Rhizobiales, and Enterobacteriales preferentially resided on S. polyrhiza. Rhizobiales are well known soil bacteria that have nitrogen-fixing relationships with members of the Fabaceae (a.k.a., Leguminosae) as well as playing a role in phosphate solubilization in legumes and non-legume land plants. The presence of rhizobia on S. polyrhiza suggests a nutrient sequestration role for S. polyrhiza. Experiments to test this hypothesis are planned.

1 - University of Detroit Mercy, Biology Dept., 4001 W. McNichols Rd., Detroit, MI, 48221, USA

Keywords:
16S rRNA
Aeromonadales
bacteria
Barcode
Giant duckweed
mesotrophic
Metagenomics
Nutrient uptake
oligotrophic
phosphate
phosphorus
Rhizobiales
Rhizobium
rhizobia
Spirodela polyrhiza.

Presentation Type: Oral Paper
Session: 22, Molecular Ecology
Location: 107/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 11:15 AM
Number: 22012
Abstract ID:700
Candidate for Awards:None