[Characterization of a thermophilic Geobacillus strain DM-2 degrading hydrocarbons].

A thermophilic Geobacillus strain DM-2 from a deep-subsurface oil reservoir was investigated on its capability of degrading crude oil under various conditions as well as its characters on degrading hydrocarbons in optimal conditions. The results showed that Geobacillus strain DM-2 was able to degrade crude oil under anoxic wide-range conditions with pH ranging from 4.0 to 10.0, high temperature in the range of 45-70 degrees C and saline concentration ranging from 0.2% to 3.0%. Furthermore, the optimal temperature and pH value for utilizing hydrocarbons by the strain were 60 degrees C and 7.0, respectively. Under such optimal conditions, the strain utilized liquid paraffine emulsified by itself as its carbon source for growth; further analysis by gas chromatography (GC) and infrared absorption spectroscopy demonstrated that it was able to degrade n-alkanes (C14-C30), branched-chain alkanes and aromatic hydrocarbons in crude oil and could also utilize long-chain n-alkanes from C16 to C36, among of which the degradation efficiency of C28 was the highest, up to 88.95%. One metabolite of the strain oxidizing alkanes is fatty acid.While utilizing C16 as carbon source for 5 d, only one fatty acid-acetic acid was detected by HPLC and MS as the product, with the amount of 0.312 g/L, which indicated that it degraded n-alkanes with pathway of inferior terminal oxidation,and then followed by a beta-oxidation pathway. Due to its characters of efficient emulsification, high-performance degradation of hydrocarbons and fatty-acid production under high temperature and anoxic condition, the strain DM-2 may be potentially applied to oil-waste treatment and microbial enhanced heavy oil recovery in extreme conditions.

[Isolation of functional bacteria guided by PCR-DGGE technology from high temperature petroleum reservoirs].

It is a brand-new method to isolate functional bacteria from high temperature petroleum reservoirs according to the sequence information obtained from PCR-DGGE patterns. Three-set primers of 16S rDNA high variable region, V3, V8, V9, were compared. The results showed that more microbial diversity information could be obtained from the PCR product of V9 region. Sequence analysis indicated that the dominant bacteria in the petroleum reservoir had high sequence similarity with bacteria from alpha, beta, gamma-Proteobacterias and Bacilli from the GenBank database. According to the sequences information, multi-cultivation technology including enrichment cultivation, special cultivation and direct cultivation methods were employed, and finally, five strains (three strains by traditional methods) were isolated from oil-water samples. Among them, three thermophilic hydrocarbon-degrading bacteria, which belonged to Bacillus sp., Geobacillus sp. and Petrobacter sp., respectively, could grow well under 55 degrees C in obligate anaerobic condition. The crude oil could be utilized by these strains with the degradation rate of 56.5%, 70.01% and 31.78% respectively along with the viscosity reduction rate of 40%, 54.55% and 29.09%, meanwhile the solidify points of crude oil were reduced by 3.7, 5.2 and 3.1 degrees C. Therefore, the combination of sequence information from PCR-DGGE and altering cultivation conditions is an available novel method to isolate more functional microorganisms which could be utilized for microbial enhanced oil recovery.

Improved biodesulfurization of hydrodesulfurized diesel oil using Rhodococcus erythropolis and Gordonia sp.

Substituted benzothiophenes (BTs) and dibenzothiophenes (DBTs) remain in diesel oil following conventional desulfurization by hydrodesulfurization. A mixture of washed cells (13.6 g dry cell wt l(-1)) of Rhodococcus erythropolis DS-3 and Gordonia sp. C-6 were employed to desulfurize hydrodesulfurized diesel oil; its sulfur content was reduced from 1.26 g l(-1) to 180 mg l(-1), approx 86% (w/w) of the total sulfur was removed from diesel oil after three cycles of biodesulfurization. The average desulfurization rate was 0.22 mg sulfur (g dry cell wt)(-1) h(-1). A bacterial mixture is therefore efficient for the practical biodesulfurization of diesel oil.