Characterization of bacterial assemblages from the rhizosphere of eastern hemlock (Tsuga canadensis) using culturing methods and molecular cloning

Characterization of bacterial assemblages from the rhizosphere of eastern hemlock (Tsuga canadensis) using culturing methods and molecular cloning

Bacteria -- Ecology

Eastern hemlock -- Microbiology

Eastern hemlock -- Roots

Eastern hemlock -- Soils

Rhizobacteria

Soil microbial ecology

Bacteria

York, Emily Ann

2008

O'Connell, Sean

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Traditionally, microbial community structure was assessed through the cultivation and isolation of microorganisms. However, bacterial species that are readily cultured in the lab may not be the most abundant within their environment and therefore may not accurately depict the microbial diversity of a sample site. To illustrate a more inclusive assessment of microbial diversity, this study incorporated two methods: cultivation and molecular cloning. The bacterial diversity of eastern hemlock rhizosphere in Albright Grove, Great Smoky Mountains National Park (G MNP), was assessed using culture-independent and modified culture-dependent methods. A longer incubation period and low nutrient media were used to culture rarely cultivated bacterial groups and attempt to bridge the gap between culture and clone libraries. Fifty isolates and one hundred and ninety-one clones were obtained, their 16S rDNA amplified using primers 341F/907R, and identified via DNA sequences submitted to the Ribosomal Database Project II. The isolates were from seven major groups, including three proteobacterial classes; the two gram positive phyla (Firmicutes and Actinobacteria); the Bacteroidtes; and the Acidohacteria, an abundant but rarely cultured bacterial division. Actinobacteria (34.0%) and Alphaproteobacteria (34.0%) co-dominated the culture collection. The clones were from ten major groups and were dominated heavily by the Acidohacteria (67.5%). The hemlock rhizosphere culture and clone collections were compared with bulk soil isolates and clones from previous studies in Albright Grove. Bacterial communities associated with the hemlock root zone were shown to be more diverse and to differ significantly from those found in bulk soil. It is best to use multiple techniques to assess diversity; however, each method in this study showed different microbial communities from bulk soil versus hemlock rhizosphere. Isolating new species - even from phyla with many cultured representatives - and interpreting their distributions will lead to better understanding of bacterial/plant interactions and ecosystem functioning.

2015-06-11

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Great Smoky Mountains National Park (N.C. and Tenn.)

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