About BHPs

Bacteriohopanepolyols or BHPs

 

aminopentol

Bacteriohopanepolyols or BHPs are groups of pentacyclic triterpenoids with an extended polyfunctionalised side chain (e.g. Rohmer, 1993). They are produced by a wide range of bacteria (e.g. Rohmer et al., 1984; Farrimond et al., 1998). Current estimates suggest less than 10% of prokaryotes are capable of biosynthesizing BHPs based on occurrence of the gene squalene hopane cyclase (sqhC; Pearson et al., 2007; Pearson and Rusch, 2009).

Structural features of BHPs in addition to the ring system can include variation in the number and nature of the functional groups in the side chain (tetra-, penta- and hexafunctionalised structures are known), methylation at C-2 or C-3, and unsaturation at C-6 and/or C-11.

BHPs

Figure 1. Generalised structure of bacteriohopanepolyols (BHPs).  Most BHPs have four, five or six functional groups on the side chain, as indicated.  Composite groups typically comprise sugar or amino acid derivatives.

The composition of these BHPs varies widely between bacterial groups and species, making biohopanoids a rich pool of molecular information in environmental samples and sediments. Analysis of a wide range of environmental samples for intact BHPs has also shown that they are ubiquitous in lacustrine, marine, and riverine sediments, soils, peats and a range of extreme environments (see Current and Past Projects).

Hopanoids are derived from BHPs and are an important and ubiquitous class of hydrocarbon biomarker compound. Said to be the most abundant group of biomarkers in the geosphere (Ourisson and Albrecht, 1992), the relative stability of the hopanoid carbon skeleton allows them to be preserved in the sedimentary record as geohopanes. Clearly the recalcitrance, ubiquity, variation and specificity of BHPs makes them ideal biomarkers, however, demonstration of the direct link with bacteria and rate of production, abundance and composition within complex natural environments are yet to be unambiguously demonstrated so many conclusions drawn regarding BHPs currently remain tentative.

 BHP to geohopane

Figure 2. Conversion of BHPs to geohopanes.

 

Further Reading:

Farrimond et al., 1998. Ancient Biomolecules 2, 147 - 166.

Ourisson, G., Albrecht, P., 1992. Acc. Chem. Res. 25, 398 - 402.

Pearson A. et al., 2007. Env. Microbiol. 9, 2175 - 2188.

Pearson, A., Rusch, D.B., 2009. The ISME Journal 3, 352 - 363. 

Rohmer, M., et al., 1984. J. Gen. Microbiol. 130, 1137 - 1150.

Rohmer, M., 1993. Pure & Appl. Chem., 65, 1293 - 1298.