Sphingomonas from petroleum-contaminated soils in Shenfu, China and their PAHs degradation abilities

Abstract

Members of the Sphingomonas genus are often isolated from petroleum-contaminated soilsdue to their unique abilities to degrade polycyclic aromatic hydrocarbons (PAHs), whichare important for in situ bioremediation. In this study, a combined phenotypic and geno-typic approach using streptomycin-containing medium and Sphingomonas-specific PCR wasdeveloped to isolate and identify culturable Sphingomonas strains present in petroleum-contaminated soils in the Shenfu wastewater irrigation zone. Of the 15 soil samplesexamined, 12 soils yielded yellow streptomycin-resistant colonies. The largest number ofyellow colony-forming units (CFUs) could reach 105CFUs g-1soil. The number of yellow CFUshad a significant positive correlation (p < 0.05) with the ratio of PAHs to total petroleumhydrocarbons (TPH), indicating that Sphingomonas may play a key role in degrading the PAHfraction of the petroleum contaminants at this site. Sixty yellow colonies were selected ran-domly and analyzed by colony PCR using Sphingomonas-specific primers, out of which 48isolates had PCR-positive signals. The 48 positive amplicons generated 8 distinct restrictionfragment length polymorphism (RFLP) patterns, and 7 out of 8 phylotypes were identifiedas Sphingomonas by 16S rRNA gene sequencing of the representative strains. Within these7 Sphingomonas strains, 6 strains were capable of using fluorene as the sole carbon source,while 2 strains were phenanthrene-degrading Sphingomonas. To the best of our knowledge,this is the first report to evaluate the relationship between PAHs contamination levels andculturable Sphingomonas in environmental samples.