Two thermophilic hydrocarbon-degrading bacteria

named N12-3 and Z3-14

were isolated from Zhan 3 block

Shengli oilfield.16S rRNA gene sequence analysis indicated that N12-3 belonged to Bacillus sp.and Z3-14 belonged to Geobacillus stearothermophilus.The n-alkane components with carbon number under 20 were preferably degraded by N12-3.After degradation

the content of alkane hydrocarbons

aromatic hydrocarbons and resin decreased by 3.59%

11.24% and 10.08% respectively

while asphalt increased by 26.01%.Furthermore

∑C21-/∑C22+ decreased from 2.62 to 0.74.On the other hand

longer n-alkane components were preferably degraded by Z3-14.After degradation

the content of saturated hydrocarbons

aromatic hydrocarbons decreased by 6.8% and 14.39% respectively

while resin and asphalt increased by 13.57% and 1% respectively. Furthermore

∑C21-/∑C22+ increased from 1.33 to 3.13.N12-3 could reduce oil viscosity by resin degradation

while Z3-14 could not.However

both strains could reduce oil viscosity by emulsification with bioemulsifiers secreted.The results suggest that microorganisms can improve oil mobility

mainly by emulsification but not by degradation.