Bacteriohopanepolyols (BHPs)

Bacteriohopanepolyols are Hopanoids with extended polyhydroxylated or amino-functionalized C₅ side chains attached to the hopane ring system. They are the intact, polar form of hopanoids produced by living bacteria and serve as both functional membrane lipids and valuable biomarkers for bacteria in the environment and geologic record.

Key Structures

• BHT (bacteriohopanetetrol): the most commonly occurring BHP in the environment; four hydroxyl groups on the side chain. Often the most abundant BHP in any sample.
• BHT II: an isomer of BHT associated specifically with suboxic and anoxic marine environments. Proposed as a biomarker for water column oxygen depletion (Sáenz et al., 2011, Organic Geochemistry).
• BHT-CE (bacteriohopanetetrol cyclitol ether): a composite structure with a cyclitol sugar ether. Dominant hopanoid in [[crocosphaera-watsonii|Crocosphaera watsonii]] (~99% of total BHP) and enriched in detergent-resistant membrane fractions (Sáenz, 2010, Organic Geochemistry).
• BHT-GCE (guanidine-modified BHT-CE): found in [[methylobacterium-extorquens|Methylobacterium extorquens]] alongside BHT-CE.
• Adenosylhopane: a likely biosynthetic intermediate and a marker for soil-derived organic matter.
• Aminotriol, aminotetrol, aminopentol: amino-functionalized BHPs associated with methanotrophic and sulfate-reducing bacteria.

Environmental Distribution

Our surveys revealed contrasting patterns across environments:

Marine water column: BHP structural diversity is low (typically 2–6 structures), dominated by BHT. Highest abundance occurs at suboxic and anoxic depths in OMZs and anoxic basins (Sáenz et al., 2011, Organic Geochemistry).

Terrigenous environments: Soils and riverine SPM have high structural diversity (up to 11 structures) and 10× greater BHP concentrations than marine SPM. Adenosylhopane is diagnostic of soil input (Sáenz et al., 2011, Organic Geochemistry).

Marine cyanobacteria: In pure culture, BHPs are restricted to nitrogen-fixing species. C. watsonii produces almost exclusively BHT-CE; Trichodesmium produces BHT-CE plus an unsaturated variant (Sáenz et al., 2012, Geobiology).

Analytical Methods

BHPs are typically analyzed by reversed-phase HPLC coupled to atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI/MSⁿ) after acetylation. Quantification uses external BHT standard curves with PD (pregnane diacetate) as internal standard. Response factors vary significantly between BHP structures, so absolute quantification is reliable only for BHT and BHpentol.