Aerobic biodegradation of hopanes and norhopanes in Venezuelan crude oils

The microbial degradation of two Venezuelan crude oils enriched in 25-norhopanes was examined after a 5-week aerobic incubation using a microbial enrichment culture. Analysis of the oils using gas chromatography–mass spectrometry revealed degradation of the C28 tricyclic terpane, the C29–C34 17α(H),21β(H)-hopanes, and the C29 17α(H),21β(H)-25-norhopane. The C35 17α(H),21β(H)-hopane and 18α(H)-oleanane were conserved. Further, the C28–C34 17α(H),21β(H)-25-norhopanes were degraded and no formation of 25-norhopanes was observed. Degradation caused preferential removal of the 22R versus the 22S isomer in both the extended hopanes and 25-norhopanes, implying that bacteria remove these compounds in aerobic environments. These data demonstrate 25-norhopane degradation on a time scale similar to that for other biomarkers.