Statistical Optimization of Crude Oil Biodegradation by Marinobacter sp. Isolated from Qeshm Island, Iran

Hydrocarbons degradation is principally achieved by microorganisms in natural environments. The extent of hydrocarbons biodegradation is mainly conditioned by environmental factors and its success depends on the optimal condition for the crude oil degrading isolates. The aims of the current study was to isolate and identify crude oil degrading bacterium from surface sediments of Qeshm Island, Iran and to evaluate the efficiency of a statistically-based experimental design for the optimization of crude oil degradation performed by the isolated strain. Crude oil degrading bacteria were isolated by serial dilutions of bacterial consortium. In order to optimize crude oil biodegradation by isolated strains, Plackett-Burman experimental design was used to evaluate nine factors affecting crude oil biodegradation in twelve experimental trials. To observe the best yield in crude oil biodegradation, factors that had higher effects were considered for the next stage in the biodegradation optimization process using the Taguchi experimental design. A gram-negative bacterium strain named as the KK1- strain (with 98% homology with Marinobacter litoralis) was isolated from enrichment consortium. Among the various variables screened using the Plackett-Burman experimental design, pH, temperature, salinity and NH4Cl were determined as the most significant factors and considered for the next stage of the biodegradation optimization process using the Taguchi experimental design. Theoretically, the optimum degradation conditions were determined to be: pH = 8, temperature = 35˚C, salinity = 30 ppt and NH4Cl = 1 g.L-1. The validity of the predicted optimized condition was tested by conducting experiments considering the predicted criteria. Biodegradation efficiency of 58.32±5.57% was achieved under the suggested conditions, which was significantly higher than that achieved by the primary conditions (35%). Indigenous bacteria from surface sediments of Qeshm Island were found to be able to degrade crude oil. Our results showed that a combination of the Plackett-Burman and the Taguchi experimental designs may be successfully used to find the optimal amounts of factors required for crude oil biodegradation.