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Georgia Journal of Science

Abstract

Pueraria montana, better known as kudzu, is an invasive species rapidly spreading throughout the southeastern United States. This plant can form root nodules which house nitrogen-fixing bacteria, allowing atmospheric nitrogen to be converted into biologically available forms of nitrogen for use by the plant host. Given the centrality of these bacteria to the spread of kudzu, isolates from nodules were characterized after collection from seven different locations across the metropolitan Atlanta area. Twenty-five isolates were grown on two different variants of nitrogen free media. Four different carbon sources were evaluated as well. Finally, growth under both aerobic and anaerobic conditions was investigated. Almost all isolates grew better under anaerobic conditions. Additionally, the carbon source and other components of the composition of the media affected growth. These data suggest significant metabolic diversity inside a relatively small geographic area posing questions about the relative contribution of nitrogen fixing bacteria to kudzu’s invasive expansion in this region. In addition, four possible “promiscuous ineffective” isolates were identified using data evaluating relative growth, possibly reflecting reduced nitrogen fixation and corresponding benefit to the host. The kudzu can be described as “promiscuous ineffective” because it allows nodulation of bacteria that have very poor nitrogen fixing capabilities. Two sequences, 16S rRNA and the gene nifD, were amplified from these four isolates. The 16S rRNA sequence reveals minor evolutionary diversity amongst isolates. Analysis of nifD reveals variations between isolates and some correspondence with an ability to fix nitrogen. With these data, further characterization of the “promiscuous ineffective” isolates may reveal the mechanism of reduced fixation rates and provide insight into possible bioremediation of kudzu.

Acknowledgements

This work was funded by a STEM mini-grant from the College of Science and Technology at Georgia Gwinnett College.

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