Analysis of Hopanoids From Three Psychrophilic Marine Bacterial Strains

Hopanoids are pentacyclic triterpenoids that are associated with the plasma membrane of some bacteria. These amphiphilic molecules, which share structural similarities with sterols, are believed to regulate the thermodynamic and mechanical properties of phospholipid packing in the cell membranes of some prokaryotes. Three psychrophilic bacterial strains isolated from Antarctica were rigorously screened for hopanoids. Past results with octadecyltrimethylammonium bromide (OTMAB), the squalene cyclase inhibitor, suggested that these bacteria might synthesize hopanoids. The bacterium, Acetobacter aceti subsp. aceti, known to contain hopanoids, was also analyzed as a control. Cellular lipids were extracted from freeze-dried cells using a chloroform/methanol/water solvent system. Crude extracts were treated with a solution of periodic acid followed by sodium borohydride reduction in order to convert the complex hopanoids to their primary alcohols. Preparative thin layer chromatography (TLC) was used to fractionate the treated extract. The treated hopanoids, recovered as TLC bands, were derivatized by acetylation, followed by gas chromatography/mass spectrometry (GC/MS) analysis. Lipid extracts from A. aceti yielded three compounds with mass spectra characteristic of hopanoids. Psychrophilic strains 116-01, 80-0 and 12-02 tested negative for these compounds