Isolation of halophilic microbial consortia capable of degrading diesel oil for the bioremediation of drilling wastes

drilling for exploration and production of petroleum requires the use of drilling fluid in order to lubricate and cool the drill bit. Oil based muds (OBMs) containing diesel, are the preferred drilling fluids because of their better lubricity. After mixing with drill cuttings, OBMs form complex industrial wastes containing hydrocarbons and brine. Bioremediation can be considered as a promising alternative to physicochemical methods for cleaning up drilling wastes because of its environmental friendly and cost effective properties. Due to high salinity and lack of active microflora in drill cuttings, developing halophilic consortia could be beneficial for enhancing bioremediation efficiency.
different oil-polluted and unpolluted saline soil and water samples have been used to enrich halophilic consortia able to degrade diesel hydrocarbons using a multistep enrichment technique. The growth capability of diesel-degrading consortia was evaluated by Bradford protein assay and standard plate count and growth curves were plotted. Furthermore, dominant strains of the consortia which were isolated from oil polluted saline soils were identified by molecular method.
Among 10 microbial consortia isolated from different environments, the best consortium was isolated from Qom oil-polluted soil sample which could grow very well on Bushnell Haas mineral medium containing diesel as the sole source of carbon. The bacterial count of the consortium was increased up to 1.88×1015 CFU/ml after 96h of incubation. Comparison of the growth curves indicated that in comparison to unpolluted samples, polluted ones reached the logarithmic phase more quickly and the final turbidity was more. 16S rRNA gene sequencing analysis revealed that the dominant strains of consortia isolated from oil polluted saline soil samples belonged to the genera of Dietzia, Microbacterium and Salinicola.
Discussion and Due to long term exposure of the polluted samples to oil pollution and high salinity, they have naturally been enriched by bacterial communities capable of degrading oil derivatives such as diesel in extreme conditions.