The aim of this work was to study the production of bioemulsifier by Rhodococcus erythropolis OSDS1, and the improvement of crude oil depletion efficiency using a consortium of petroleum hydrocarbon degraders and OSDS1. The results showed that R. erythropolis OSDS1 produced highly stable bioemulsifier under various salinity (0-35 g/L NaCl) and pH (5.0-9.0) conditions; more than 90% of the initial emulsification activity was retained after 168 h. Emulsification capacity of the bioemulsifier on different petroleum hydrocarbons was diesel > mineral oil/crude oil > gasoline. A mixed bacterial consortium combining OSDS1 and four other petroleum hydrocarbon degraders was constructed. GC-MS results revealed that the constructed consortium achieved 85.26% depletion efficiency of crude oil in 15 days, which was significantly higher than that of individual strains. During the process, alkane hydroxylase gene (alkB) was successfully amplified from the consortium, confirming presence of crude oil degrading enzymes.

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a b s t r a c tThis research is part of a multidisciplinary research program to develop a bioremediation protocol for a solid waste management (SWM) site in Northern California -a site which is heavily contaminated with petroleum hydrocarbons. In this initial study, 30 bacterial strains were isolated and evaluated for their efficiencies to deplete crude oil. The 3 most efficient bacterial isolates for crude oil depletion were designated as S1BD1, OPKDS2, and OSDS1; they were identified as Serratia proteamaculans, Alcaligenes sp. and Rhodococcus erythropolis, respectively, based on partial 16S rRNA gene sequences. Determination of crude oil depletion efficiency by gas chromatographyemass spectrometry (GC-MS) revealed that Serratia proteamaculans S1BD1 was the most efficient (68.0 ± 1.78%), followed by Alcaligenes sp. OPKDS2 (63.7 ± 3.28%), and Rhodococcus erythropolis OSDS1 (54.9 ± 5.07%). S. proteamaculans S1BD1 was able to deplete a wide spectrum of carbon compounds within the individual components of crude oil. Alcaligenes sp. OPKDS2 was the most efficient at depleting BTEX (91.2 ± 1.90%), and R. erythropolis OSDS1 exhibited a substrate preference of n-alkanes. All three strains exhibited unusually high crude oil depletion efficiencies and tolerated a wide range of salinity and pH levels, which makes them excellent candidates for bioaugmentation of the SWM site.

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