Monitoring the Impact of Hydrocarbon Contamination and Nutrient Addition on Microbial Density, Activity, and Diversity in Soil

The development of optimal in situ bioremediation strategies requires a better knowledge of their impact on the soil microbial communities. We have evaluated the impact of hexadecane contamination and different nutrient amendments on soil microbial density and activity. Microbial density was measured via total DNA quantification, and microbial activity via respiration and RNA variation. The RNA/DNA ratio was also determined, as it is a potential indicator of microbial activity. PCR-amplified 16S rRNA genes were cloned and sequenced to analyze the diversity of bacterial communities. Nutrient addition significantly increased respiration and DNA and RNA concentrations in contaminated soil, indicating a limitation of degradation and growth by the availability of nitrogen and phosphorus in unamended microcosms. Hexadecane treatment slightly affected the diversity of the bacterial community, while it was dramatically reduced by nutrient treatments, particularly the addition of nitrogen and phosphorus. Microbial community composition was also altered with the enrichment of populations related to Nocardia in bioremediated soils, while uncultured Proteobacteria were mostly detected in uncontaminated soil.