Bacterial degradation of the petroleum biomarker cholestane

A petroleum isolated bacterium, later identified as Mycobacterium fortuitum was cultured in the presence of pristane and various isomers of cholestane. The cholestane isomers were found to be differentially degraded, resulting in the following degradation sequence: {dollar}5alpha, 14alpha, 17alpha,{dollar} 20R-cholestane {dollar}>{dollar} 5{dollar}alpha, 14beta, 17beta,{dollar} 20R-cholestane and 5{dollar}alpha, 14alpha, 17alpha, 20{dollar}S-cholestane {dollar}>{dollar} 5{dollar}alpha, 14beta, 17beta{dollar}, 20S-cholestane. However, the same cholestane isomers cultured in the presence of dodecane, in lieu of pristane were not degraded. The pristane, therefore promoted the degradation of the cholestane isomers, most likely by inducing a degradative mechanism capable of utilizing cholestane as a substrate. A structural comparison of the cholestane isomers to each other, and the cholestane molecule to pristane is used to provide an explanation for the above listed observations.