Anaerobic biodegradation of the isoprenoid biomarkers pristane and phytane

Abstract

Isoprenoids, a diverse class of compounds synthesized by all three domains of life, comprise many of the biomarker compounds used in paleoenvironmental and paleoecological reconstruction of Earth history. These biomarkers include hopanoids, sterols and archaeal membrane lipids. While changes in hydrocarbon profiles in anoxic sediments and oilfields indicate that anaerobic microbial metabolism is involved in the disappearance or alteration of isoprenoids, direct links between specific compounds and their microbial degraders are lacking. Here we describe pristane (Pr) and phytane (Ph) degradation associated with NO^-_3 reduction. We confirmed isoprenoid conversion to CO_2 using ^(13)C-labeled Ph. After 120 days, dissolved inorganic carbon (DIC) produced in incubations grown with ^(13)C-labeled Ph had a δ^(13)C value of +76.7 ± 11.9‰, significantly higher than values for incubations with unlabeled Ph (−35.7 ± 2.0‰) and those without an added carbon substrate (−30.0 ± 2.1‰). Additional incubations, displayed NO^-_3 reduction after amendment with archaeal diphytanyl glycerol diether (DGD) core lipids, but not in those amended with glycerol diphytanyl glycerol tetraether (GDGT) core lipids. Both 16S rRNA clone libraries and whole cell rRNA-targeted fluorescent in situ hybridization (FISH) indicated that the likely Pr and Ph degrading Bacteria were Gamma proteobacteria, with > 99% similarity to Pseudomonas stutzeri.