Influence of crude oil contamination on the bacterial community of semiarid soils of Patagonia (Argentina)

Autochthonous bacteriocenoses in semiarid soils in Patagonia were found to be capable of rapidly adapting to high contamination with crude oil. This a daptation at community level is due to the selective enrichment of hydrocar bon-utilizing bacteria always present in these soils, immediately after a h eavy contamination with crude oil, the autochthonous bacteriocenosis contai ned about 28% hydrocarbon-utilizing bacteria which could be classified into eight ecotypes with characteristic metabolic profiles. Mainly n-alkanes we re used as growth substrates of representative strains. After seven months' exposure to crude oil, the bacteriocenosis consisted almost entirely of hy drocarbon-utilizing bacteria. At least fourteen ecotypes were distinguishab le, and the majority of representative strains were able to metabolize a br oad spectrum of aliphatic and aromatic hydrocarbons. Corresponding to the s ignificant alteration of the physiological diversity, drastic changes to th e taxonomic diversity were also found. Whereas at the beginning of the stud y the autochthonous bacteriocenoses were dominated by GRAM-POSITIVE genera of the Actinomycetales (Dietzia, Gordona, Nocardia, Rhodococcus, Streptomyc es) with high ecological potency, after just two months' exposure to crude oil, GRAM-negative bacteria (especially Pseudomonas stutzeri) became predom inant within the hydrocarbon-utilizing bacteriocenoses accompanied by some GRAM-positive genera of the Actinomycetales with a significantly lower abun dance. These findings underline the importance of Pseudomonas and some gene ra of Actinomycetales for processes of natural attenuation and the technica lly supported in situ bioremediation of soil polluted by crude oil in Patag onia.