Molecular characterization of the alkB gene in the thermophilic Geobacillus sp. strain MH-1.

An extremely thermophilic alkane-degrading bacterium, strain MH-1, was isolated from the deep subterranean petroleum reservoir in Shengli oil field, PR China. Based on its physiological characteristics and analysis of its 16S rRNA gene sequence, strain MH-1 was identified as Geobacillus stearothermophilus. Strain MH-1 was able to grow at temperatures ranging from 50 to 72 degrees C and effectively degraded hexadecane as the sole carbon source at 70 degrees C. Strain MH-1 degraded alkanes with different length chains (C(12)-C(31)) in crude oil, but it preferentially degraded middle chain-alkanes. The alkane hydroxylase system of G. stearothermophilus MH-1 was characterized. It contained at least three alkane monooxygenase gene homologs (alkB-geo1, alkB-geo4, and alkB-geo6). The AlkB-geo6 cluster, which had a high sequence similarity to the alkB2 cluster of Rhodococcus strains NRRL B-16531 and Q15, contained alkB-geo6, two rubredoxins and a putative transcriptional regulatory protein.