Determining sensitivity to heavy metals in surfactant-producing bacteria and their efficiency in removing Total petroleum hydrocarbons

Due to the association of some heavy metals with petroleum hydrocarbons, the use of native degrading bacteria of surfactant-producing oil that is resistant to heavy metals is one of the priorities of bioremediation technology. For this purpose, in this study, 39 alkane-degrading and biosurfactant-producing strains were used (isolated from saline soils contaminated with oil in the oil-rich areas of southern Khuzestan province) belonging to the soil microbiology laboratory gene bank of Tehran University. Then, the sensitivity of the isolates to different concentrations (40 to 80 ppm) of heavy metals (chromium, lead, copper, nickel, and cadmium) was tested. The results showed that only three strains Ochrobactrum lupini</em> strain SH23, Ochrobactrum lupini</em> strain SH24, and Bacillus subtilis</em> subsp. Inaquosorum</em> strain SH34 could grow in the presence of all heavy metals. The effects of different concentrations of heavy metals on the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of selected bacteria showed that Ochrobactrum lupini</em> strain SH23 had the highest tolerance to heavy metals. The evaluation of the ability to degrade petroleum hydrocarbons in the presence of heavy metals by selected bacteria showed that the microbial consortium (SH23, SH24, and SH34) and Ochrobactrum lupini</em> strain SH23 were able to degrade 71 and 64% of crude oil with a concentration of 0.5% (v/v), respectively after 10 days of aeration at 30 0C. The findings of this research proved that by conducting additional environmental studies, the bacterium Ochrobactrum lupini</em> strain SH23 can be used in the treatment of water and wastewater contaminated with petroleum hydrocarbons and heavy metals.