Biodegradation of Heavy Crude Oil Using Persian Gulf Autochthonous Bacterium

Abstract

Petroleum hydrocarbons are potential sources of soil and water contamination. There are various clean-up technologies for removal of these crude spilled oil pollutants, such as microorganisms of different ecosystems. In the present study the capability of an autochthonous Rhodococcus ruber KE1, which was previously isolated from Persian Gulf water and sediment (Khark Island, south part of Iran), was evaluated for biodegradation of the contaminated seawater by Iranian exported heavy crude oil. In the crude oil biodegradation, both biotic and abiotic factors should be considered. So biotic factors such as growth curve of the Rhodococcus ruber KE1 have been studied. Results demonstrated that the maximum colony count was achieved to 9.50 × 109 cfu mL−1 after 26 h then reached to the death phase. The specific growth rate constant (μ) of the bacteria in logarithmic phase and mean generation times are calculated 0.10 h−1 and 3.02 h, respectively. Also different physical parameters such as pH, temperature, crude oil concentration, and agitation speed were optimized to achieve the maximum degradation efficiency. The best results were obtained at pH 8.5, temperature 40 °C, agitation speed of 250 rpm, and crude oil concentration 1% (v/v). The related data showed that Rhodococcus ruber KE1 in favourable conditions was able to degrade about 90% of total hydrocarbons after a week. The residual was analyzed for nitrogen- and sulfur-containing compounds using CHNS technique. Total nitrogen and sulfur were decreased 48 and 44%, respectively. The ability of this specific strain, as a surfactant producer was investigated under optimal conditions. A reduction in surface tension from 60 (control) to 26 mN/m was achieved. To the best of our knowledge, this is the first report of isolated Rhodococcus ruber KE1 from Persian Gulf, which has the ability to degrade crude oil and at the same time produce biosurfactant in a week’s time. The results indicated that autochthonous Rhodococcus ruber KE1 may be a good option to be utilized as a crude oil degrader.