Rhizosphere microbial communities of Puccinella angustata thriving in pristine diesel-contaminated Arctic soils

Petroleum hydrocarbon contamination has reached Arctic soils, Puccinellia angustata thrives in such habitats. Hydrocarbon removal during phytoremediation treatments strongly depends on the catabolic activities of root associated microorganisms. This research compared the rhizospheric microorganisms from P. angustata established at Arctic soils under different degrees of contamination with petroleum hydrocarbons to determine if this plant species has phytoremediation potential. The abundance, diversity, and activity of soil bacterial communities were investigated by means of plate and microscopic counts, strains isolation, 16S rRNA gene DGGE fingerprinting, functional gene PCR detection, microcosm hydrocarbon mineralization assays, and TPH quantification. This study was divided in three experimental stages. In the first stage a comparison of samples vegetated by five different plant species as well as four bulk samples, showed that P. angustata had greater enrichment of hydrocarbon-degrading bacteria than samples vegetated by other plant species. In the second stage, a comparison between the rhizosphere of P. angustata and bulk samples collected at pristine (Pr), hydrocarbon-contaminated but non-bioremediated (NBr) and hydrocarbon-contaminated and bioremediated (Br) Arctic soils, revealed that the presence of P. angustata enhanced the abundance and the activity of hydrocarbon-degrading microorganisms in two soils (Pr and NBr) but not at Br since this soil was subjected to fertilizations as bioremediation process. In the third stage, via growth chamber experiments, in which high Arctic summer conditions were simulated, P. angustata (with and without nitrogen fertilization) was assessed for phytoremediation of a soil artificially contaminated with diesel (10,000 mg Kg-1). Puccinellia showed tolerance to fresh diesel contamination and enhanced hydrocarbon-degrading bacteria that significantly increased the TPH removal. Also, the rhizosphere of P. angusatata had high bacterial diversity, encompassing members from Actinobacteria, Bacteroidetes, Firmicutes, Gemmatimonadetes and Proteobacteria phyla. These findings indicate that P. angustata stimulates soil microflora responsible for biodegradation of hydrocarbons therefore it has potential for phytoremediating contaminated Arctic soils.Abbreviation: PCR (polymerase chain reaction), DGGE (Denaturing Gradient Gel Electrophoresis), TPH (Total Petroleum Hydrocarbons).%%%%La contamination par hydrocarbures petroliers a touche les sols arctiques ; Puccinellia angustata se developpe dans ces habitats. L'elimination de l'hydrocarbure pendant les traitements de phytoremediation depend fortement des activites cataboliques des microorganismes associes a la racine. Cette recherche a compare les microorganismes rhizospheriques de P. angustata etablis dans les sols arctiques a differents niveaux de contamination par hydrocarbures petroliers pour determiner si cette espece de plante a du potentiel pour la phytoremediation. L'abondance, la diversite, et l'activite des communautes…