Previous studies have determined that introduced plant species can alter microbial community dynamics.  This studied evaluated the impacts of a severe infestation of an invasive species, Alliaria petiolata, on microbial community dynamics in a forest soil. We sampled areas of infestation vs. non-infestation within a sand prairie pine plantation in central Illinois using several techniques to evaluate bacterial activity. In situ measurements of total soil respiration showed significant increases in CO₂ efflux for infested sites.  In vitro, carbon mineralization was evaluated on unamended and amended garlic mustard and non garlic mustard soils. These soils were exposed to 12 different carbon/nitrogen treatments over 20 days and resulted in a 2-fold increase in the output of CO₂ for infested soils treated with glucose and a nitrogen source. Nitrogen mineralization rates were evaluated using thirty-two day incubations.  There were significant increases in nitrification in infested soils. Microbial community dynamics were further evaluated by inoculating soil slurries on non-selective nutrient agar plates and nitrogen free selective agar plates. Direct counts of colonies on selective plates revealed an almost ten-fold increase in bacteria for infested soils. These studies suggest that Alliaria petiolata infestations shift microbial community structure by increasing the population of free-living nitrogen fixing bacteria.  As garlic mustard is currently invading forests at high rates there is a concern that changes in microbial community structure will alter nutrient availability or competitive dynamics of aboveground biomass and alter nutrient dynamics of North American forests.