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    Culturability, Temporal Change, Phylogenetic Analysis, And Yield Of Bacterial Communities In A Subarctic Lake: Harding Lake

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    Author
    Zhao, Xiaoming
    Chair
    Button, Don
    Keyword
    Biochemistry
    Molecular biology
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    URI
    http://hdl.handle.net/11122/8887
    Abstract
    Heterotrophic bacteria, adapted to small concentrations of substrate, are a main component of the microbial flywheel. However, understandings of their activity, isolation, genetics, and nutrition are restricted to the large, easily isolated and culturable bacteria. By using the dilution culture method, apparent culturabilities could approach 10% in unamended lake water and were inversely proportional to the number of cells inoculated from mixed species in a natural environment from Harding Lake. Substrate additions could not improve bacterial culturability in the dilution cultures. Comparative sequence analyses of 16S rDNA genes showed that all bacterial species have similar lengths in the phylogenetic tree, suggesting similar evolution rates. These indicated close relationships among the six bacterial divisions: alpha-proteobacteria, beta-proteobacteria, gamma-proteobacteria, cytophaga/flexibacter/bacteriodes, acidobacteria, and cyanobacteria. Possible reasons include that metabolic enzymes of these bacteria were modified to adapt to low temperatures from tropical temperatures in arctic areas at the same time. These findings may provide insight into the recent evolution of the bacteria in near polar freshwater. Moreover, a high abundance of alpha-proteobacteria and gamma-proteobacteria was found in Harding Lake, suggesting high growth rates of these bacteria in the freshwater region. This is consistent with a rapid continuous shift in the distribution of dominant species observed in Harding Lake, according to the TRFLP, DGGE, and flow cytometry data. Our results also suggested that input of dissolved organic matter derived from terrestrial plants and soils, introduction of terrestrial bacteria, and bacteria themselves led to the bacterial species shifts associated with the seasonal change. Bacterial growth yield is used to measure this carbon conversion efficiency. However, bacterial growth yields have been seriously underestimated in previous studies. Our in situ values for bacterial growth yield from an amino acid mix were actually closer to 50% and 70% in active systems by using a modified, sensitive and accurate method and increased with the increase of temperature between 1�C and 6�C.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 2005
    Date
    2005
    Type
    Dissertation
    Collections
    Chemistry and Biochemistry

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