Director & Technical Advisor
Although an unfamiliar molecule to many petroleum geochemists, bacteriohopanetetrol (BHT) is nevertheless an important one, being a major source of the hopanes found in oils and their source rocks (Ourisson et al., 1984). BHT is probably the most common of the many different hopanoid structures found in the membranes of a wide range of bacteria; it also has the simplest structure of those with a side chain – others can have complex functional groups attached, but I’ll leave those for another day!
Because of its diverse occurrence in bacteria, BHT is ubiquitous in modern soils and sediments. During diagenesis associated with progressive sediment burial the alcohol groups undergo various reactions including forming linkages that incorporate hopanoids into kerogen (Farrimond et al., 2003). Many of these kerogen-bound hopanoids retain the original C35 bacteriohopanoid structure intact, but with increasing maturation and the onset of hydrocarbon generation, a series of hopane products are released (C27 and C29 to C35) due to various extents of cracking of the side chain. The relative abundance of the different hopane homologues in an oil is a function of these complex reactions and the range of the original biohopanoids preserved in the source rock – not only BHT but a diverse range of similar bacterial hopanoids. These controls are still not fully understood and warrant further research.
References:
Farrimond, P., Love, G.D., Bishop, A.N., Innes, H.E., Watson, D.F. & Snape, C.E. (2003). Evidence for the rapid incorporation of hopanoids into kerogen. Geochimica et Cosmochimica Acta 67, 1383-1394.
Ourisson, G., Albrecht, P. & Rohmer, M. (1984). The Microbial Origin of Fossil Fuels. Scientific American 251, 44-51.
