Background: Increasing worldwide contamination with hydrocarbons has urged environmental remediation using biological agents such as bacteria. Our goal here was to study the phylogenetic relationship of two crude oil degrader bacteria and investigation of their ability to degrade hydrocarbons.

Materials and Methods: Phylogenetic relationship of isolates was determined using morphological and biochemical characteristics and 16S rDNA gene sequencing. Optimum conditions of each isolate for crude oil degradation were investigated using one factor in time method. The rate of crude oil degradation by individual and consortium bacteria was assayed via Gas chromatography–mass spectrometry (GC-MS) analysis. Biosurfactant production was measured by Du Noüy ring method using Krüss-K6 tensiometer.

Results: The isolates were identified as Dietzia cinnamea KA1 and Dietzia cinnamea AP and clustered separately, while both are closely related to each other and with other isolates of Dietzia cinnamea. The optimal conditions for D. cinnamea KA1 were 35°C, pH9.0, 510 mM NaCl, and minimal requirement of 46.5 mM NH4Cl and 2.10 mM NaH2PO4. In the case of D. cinnamea AP, the values were 30°C, pH8.0, 170 mM NaCl, and minimal requirement of 55.8 mM NH4Cl and 2.10 mM NaH2PO4, respectively. Gas chromatography – Mass Spectroscopy (GC-MS) analysis showed that both isolates were able to utilize various crude oil compounds, but D. cinnamea KA1 was more efficient individually and consortium of isolates was the most. The isolates were able to grow and produce biosurfactant when cultured in MSM supplemented with crude oil and optimization of MSM conditions lead to increase in biosurfactant production.

Conclusion: To the best of our knowledge this is the first report of synergistic relationship between two strains of D. cinnamea in biodegradation of crude oil components, including poisonous and carcinogenic compound in a short time.