| The studies presented here used bacterial enrichment cultures to examine the distribution and extent of biomarker-degrading activity in aerobic and anaerobic environments.; The biodegradation of C30 17alpha,21beta(H)-hopane within Bonny Light crude oil by laboratory enrichment cultures was demonstrated to be temperature sensitive through incubation at 4°C, 15°C, 30°C, and 37°C. Although degradation of the n-alkanes and the branched alkanes, pristane and phytane, was observed at 15°C, 30°C, and 37°C, the degradation of hopane was limited to 30°C. At 4°C, no degradation of any crude oil components was observed. DGGE analysis of the cultures at these different temperatures revealed no striking differences in the composition of the microbial communities.; The aerobic microbial degradation of two Venezuelan crude oils enriched in 25-norhopanes was examined after a five-week aerobic incubation using the Light Crude (LC) enrichment culture, an enrichment culture developed from a creosote-contaminated soil and previously shown to degrade the C30 17alpha,21beta(H)-hopane. After five weeks, analysis of the Venezuelan oils using gas chromatography-mass spectrometry revealed extensive biomarker degradation. The C28 tricyclic terpane, C29--C 34 17alpha(H),21beta(H)-hopanes, and the C29 17alpha(H),21beta(H)-25-norhopane were all degraded. The C35 17alpha(H),21beta(H)-hopane and 18alpha(H)-oleanane were conserved. Further and previously unreported, the C28--C34 17alpha(H),21beta(H)-25-norhopanes were degraded and no formation of 25-norhopanes was observed. Degradation caused preferential removal of the 22R versus the 22 S isomer in both the extended hopanes and 25-norhopanes, implying that bacteria remove these compounds in aerobic environments. These data also demonstrated 25-norhopane degradation on a time scale similar to other biomarkers, suggesting that the 25-norhopanes and hopanes share a microbial mechanism of degradation.; The potential cometabolic mechanisms of C30 17alpha,21beta-hopane transformation were examined using the Degraded Light Crude (DLC) enrichment culture and a Hopane-Enriched Fraction (HEF) of Bonny Light crude oil. These studies demonstrated hopane degradation within HEF, suggesting that the degradation of C30 17alpha,21beta(H)-hopane by the DLC culture is not cometabolic. The elucidation and description of aerobic and anaerobic mechanisms of biomarker transformation may reveal metabolically distinct routes that can be used as signatures of aerobic and anaerobic transformations. (Abstract shortened by UMI.)... |
