Alkanindiges illinoisensis gen. nov., sp. nov., an obligately hydrocarbonoclastic, aerobic squalane-degrading bacterium isolated from oilfield soils.

An alkane-degrading bacterium, designated GTI MVAB Hex1(T), was isolated from chronically crude oil-contaminated soil from an oilfield in southern Illinois. The isolate grew very weakly or not at all in minimal or rich media without hydrocarbons. Straight-chain aliphatic hydrocarbons, such as hexadecane and heptadecane, greatly stimulated growth; shorter-chain (</=C(15)) hydrocarbons did not (with decane as the sole exception). Growth was also greatly enhanced by the branched aliphatic hydrocarbons pristane and squalane. The latter of these was most intriguing, as catabolism of squalane has hitherto been reported only for Mycobacterium species. Although unable to utilize mono- or polycyclic aromatic hydrocarbons as sole carbon sources, the isolate did show slight fluorene-mineralizing capability in Luria-Bertani medium, which was partially repressed by hexadecane. In contrast, hexadecane supplementation greatly increased mineralization of (14)C-dodecane, which was not a growth substrate. Further testing emphasized the isolate's extremely narrow substrate range, as only Tween 40 and Tween 80 supported significant growth. Microscopic examination (by scanning and transmission electron microscopy) revealed a slightly polymorphic coccoidal to bacillar morphology, with hydrocarbon-grown cells tending to be more elongated. When grown with hexadecane, GTI MVAB Hex1(T) accumulated a large number of electron-transparent intracytoplasmic inclusion bodies. These were also prevalent during growth in the presence of squalane. Smaller inclusion bodies were observed occasionally with pristane supplementation; they were, however, absent during growth on crude oil. On the basis of 16S rRNA gene sequence data and range of growth substrates, classification of this isolate as the type strain of Alkanindiges illinoisensis gen. nov., sp. nov. is proposed, which is most closely related (approx. 94 % sequence similarity) to Acinetobacter junii.