DNA stable isotope probing reveals contrasted activity and phenanthrene-degrading bacteria identity in a gradient of anthropized soils

International audiencePolycyclic aromatic hydrocarbons (PAHs) are ubiquitous soil organic pollutants. Although PAH degrading bacteria are present in almost all soils, their selection and enrichment have been shown in historically high PAH contaminated soils. We can wonder if the effectiveness of PAH biodegradation and the PAH-degrading bacterial diversity differ among soils. The stable isotope probing (SIP) technique with 13 C-phenanthrene (PHE) as a model PAH was used to: i) compare for the first time a range of ten soils with various PAH contamination levels, ii) determine their PHE-degradation efficiency, and iii) identify the active PHE-degraders using 16S rRNA gene amplicon sequencing from 13 C-labelled DNA. Surprisingly, the PHE degradation rate was not directly correlated to the initial level of total PAHs and phenanthrene in the soils, but was mostly explained by the initial abundance and richness of soil bacterial communities. A large diversity of PAH-degrading bacteria was identified for seven of the soils, with differences among soils. In the soils where the PHE degradation activities were the higher, Mycobacterium species were always the dominant active PHE degraders. A positive correlation between PHE-degradation level and the diversity of active PHE-degraders (Shannon index) supported the hypothesis that cooperation between strains led to a more efficient PAH degradation