Seasonal Shifts in Soil Bacterial Diversity in Southwestern Pennsylvania

Abstract

Soil bacteria are essential components of terrestrial ecosystems. Soil bacterial composition and distribution are affected by anthropogenic factors as well as fluctuations in naturally occurring environmental factors such as the change in seasons. In this study, a total of 438 culturable heterotrophic soil bacteria were isolated in the winter, fall and summer so as to evaluate the effects of seasons on bacterial diversity in Southwestern Pennsylvania. 16S rDNA sequences of the isolated bacteria were analyzed in the microbial community analysis platform, MOTHUR. We found that the same phyla were represented in all seasons, albeit to different levels. While Bacteroidetes were most common in the winter, Firmicutes dominated during the summer. Firmicutes and Gamma-Proteobacteria were isolated throughout the year. Bacterial diversity fluctuated between seasons, being highest in the summer with 57 different bacterial species and lowest in the winter with 25 different bacterial species. Thus, this study has not only illustrated seasonal shifts in soil bacterial diversity, but has also been useful in establishing a baseline of soil bacterial diversity in this region of Southwestern Pennsylvania. Continued monitoring of soil bacterial diversity will enable long-term ecological monitoring and study of the potential environmental impacts of the Marcellus shale gas drilling.