Structural diversity of the triterpenic hydrocarbons from the bacterium Zymomonas mobilis: the signature of defective squalene cyclization by the squalene/hopene cyclase.

Twelve polycyclic triterpenic hydrocarbons (alpha- and gamma-polypodatetraenes, dammara-20(21),24-diene, 17-isodammara-12,24-diene, eupha-7,24-diene, hop-17(21)-ene, neohop-13(18)-ene, 17-isodammara-20(21),24-diene, neohop-12-ene, fern-8-ene, diploptene and hop-21-ene) were detected in the hydrocarbon fraction from the bacterium Zymomonas mobilis. Some of them have never been reported from bacteria. These triterpenes were present in Z. mobilis in significant amounts, comparable to those of diploptene, which is usually the major triterpenic hydrocarbon in hopanoid-producing bacteria. The occurrence of such compounds confirms the lack of specificity of bacterial squalene cyclases and the possibility of alternative cyclization routes induced by the existence in the cyclization process of intermediate carbocations of sufficient lifetime.