Characterization and Interactions of Soil Microbial Communities in Five Physiographic Regions and the Rhizosphere of Common Weeds

Kelsey Brown, Franklin Irvin, Julia Stevens


This paper explores the symbiotic bacteria and the antimicrobial activity of the common weeds Plantago major and Trifolium repens, as well as those of North Carolina soils collected from five physiographic regions. The purpose of this study is to characterize the diversity and interactions of symbiotic microbes in the rhizosphere of prolific weeds and different soil types. Cell cultures and isolations were taken from the rhizosphere, phyllosphere, and endosphere of each weed sample as well as bulk soil collected from Blue Ridge Mountains, Piedmont, Sandhills, Lower Coastal Plain, and Upper Coastal Plain physiographic regions. Competition assays between isolates were performed and a final set of disc diffusion assays were conducted to test effectiveness of prolific weed-associated bacteria against E. coli. The T. Repens associated bacteria produced the highest degree of inhibition against E. coli with 33.3% of its symbiotic bacteria displaying inhibition. No microbes from P. major were able to inhibit E. coli. When competing T. repens and P. major microbe isolates against one another, 60.38% participated in microbial warfare. For the regional soil types, 35.3% of Mountain, 85% of Piedmont, 71.4% of Upper Coastal, 80% of Lower Coastal, and 33.3% of Sandhills microbes showed zones of inhibition. The Mountain region exhibited the highest degrees of inhibition, while the Lower Coastal region exhibited the lowest degrees. The Mountain and Lower Coastal regions also displayed the largest amount of microbial diversity. In addition to understanding interactions between microbes and their symbiotic effects for plants, these microbes could also serve as the basis for future explorations into natural product discovery.


North Carolina; Microbiology; Secondary Metabolism; Microbial Inhibition

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