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Front Microbiol. 2017 May 30;8:949. doi: 10.3389/fmicb.2017.00949. eCollection 2017.

Nutrient Stoichiometry Shapes Microbial Community Structure in an Evaporitic Shallow Pond.

Author information

1
School of Life Sciences, Arizona State University, TempeAZ, United States.
2
School of Earth and Space Exploration, Arizona State University, TempeAZ, United States.
3
Department of Statistics, Rice University, HoustonTX, United States.
4
J. Craig Venter Institute, La JollaCA, United States.
5
Department of Biology and Biotechnology Graduate Program, American University in CairoNew Cairo, Egypt.
6
Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, La JollaCA, United States.
7
Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de MéxicoCiudad de México, Mexico.
8
Flathead Lake Biological Station, University of Montana, PolsonMT, United States.

Abstract

Nutrient availability and ratios can play an important role in shaping microbial communities of freshwater ecosystems. The Cuatro Ciénegas Basin (CCB) in Mexico is a desert oasis where, perhaps paradoxically, high microbial diversity coincides with extreme oligotrophy. To better understand the effects of nutrients on microbial communities in CCB, a mesocosm experiment was implemented in a stoichiometrically imbalanced pond, Lagunita, which has an average TN:TP ratio of 122 (atomic). The experiment had four treatments, each with five spatial replicates - unamended controls and three fertilization treatments with different nitrogen:phosphorus (N:P) regimes (P only, N:P = 16 and N:P = 75 by atoms). In the water column, quantitative PCR of the 16S rRNA gene indicated that P enrichment alone favored proliferation of bacterial taxa with high rRNA gene copy number, consistent with a previously hypothesized but untested connection between rRNA gene copy number and P requirement. Bacterial and microbial eukaryotic community structure was investigated by pyrosequencing of 16S and 18S rRNA genes from the planktonic and surficial sediment samples. Nutrient enrichment shifted the composition of the planktonic community in a treatment-specific manner and promoted the growth of previously rare bacterial taxa at the expense of the more abundant, potentially endemic, taxa. The eukaryotic community was highly enriched with phototrophic populations in the fertilized treatment. The sediment microbial community exhibited high beta diversity among replicates within treatments, which obscured any changes due to fertilization. Overall, these results showed that nutrient stoichiometry can be an important factor in shaping microbial community structure.

KEYWORDS:

algae; bacteria; beta diversity; community structure; growth rate hypothesis; rRNA gene copy number; stoichiometry

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