Phenanthrene‐Degrader Community Dynamics in Rhizosphere Soil from a Common Annual Grass

Abstract

AbstractEnhanced rates of phenanthrene biodegradation were observed in rhizosphere soils (17.2 and 15.5 mg/kg/d for initial and re‐spiked additions, respectively) planted with slender oat (A vena barbata Pott ex Link) compared with unplanted bulk soil controls (12.4 and 10.7 mg/kg/d). Soil microbial populations were characterized using a modified most probable number (MPN) method to determine quantitative shifts in heterotrophic and phenanthrene degrader communities while principal component analysis (PCA) of fatty acid methyl ester (FAME) data from isolated phenanthrene degraders was used to identify qualitative differences and degrader community diversity. The average heterotrophic bacterial population over time was about three times larger in rhizosphere soil than in bulk soil while phenanthrene degrading populations increased by as much as an order of magnitude between 24 and 28 days after planting (DAP). Thus, phenanthrene degraders were selectively enriched in rhizosphere soil compared with bulk soil. The greatest selection for degraders occurred during the later stages of plant development from 24 to 32 DAP. A PCA plot of the FAME data from phenanthrene degrader isolates indicated that the rhizosphere degraders were less diverse than bulk soil degraders. These results give us some insight into the mechanisms responsible for enhanced biodegradation and selective degrader enrichment in rhizosphere soils.