Abiotic and biological hopanoid transformation: towards the formation of molecular fossils of the hopane series

Tritium labeled hopane and bacteriohopane were incubated in the presence of the bacterium Arthrobacter simplex. In both experiments, the corresponding 17(21)-olefins and 17,21-epoxides were formed from the saturated hydrocarb on. In addition, hop-17(21)-en-20-one, 17,21-secohopane-17,21-dione and tri norhopan-21-one were found in the case of the hopane incubation, Control ex periments were performed in the absence of the bacteria either with the cul ture medium alone or with the culture medium containing the non-ionic surfa ctant Emulphogene(R). Tritium labeled hop-17(21)-ene and 17,21-epoxyhopane were incubated under the same conditions. Only the 17(21)-olefins and proba bly to some extent the 17,21-epoxides, resulted from the bioconversion of t he corresponding saturated hopanoids. The other hopanoids were formed by th e abiotic oxidation of hop-17(21)-ene. Their formation was however favored by the presence of the bacteria or of the non-ionic surfactant Emulphogene( R), suggesting that dispersion of the hydrophobic hopanoid in the aqueous p hase was essential for the oxidative degradation. Surprisingly, no degradat ion of the n-alkyl chain of bacteriohopane was observed. (C) 1999 Elsevier Science Ltd. All rights reserved.