Fossil steroid acids can arise from microbial alteration of steranes

• Published in: Organic geochemistry Vol. 194; p. 104816
• Main Authors: Xie, Can, Zhu, Gangtian, Hou, Yuguang, He, Zhiliang
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.08.2024
• Subjects: Biodegradation; biomarkers; carbon; Carboxyl group; fossils; Molecular fossil; oxidation; petroleum; Sterane; Steroid acids; Biodegradation; Sterane; Carboxyl group; Molecular fossil; Steroid acids
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/j.orggeochem.2024.104816

•Origin of steroid acids by biodegradation of steranes observed for the first time.•Aerobic bacteria can oxidize the terminal methyl group of steranes to form steroid acids.•The substitution at C-24 affects isomerization of C-5 for steroid acids.•Terminal carboxylation at side chain of steranes generates 25S and 25R steroid acids. Steroid acids are unique molecular fossils composed of a steroid carbon skeleton linked to a carboxyl group. These biomarkers contain special geological and biological clues in their structures. However, the origin of steroid acids remains a subject of debate, and there is a lack of direct evidence in previous studies. Here, we present experimental evidence for the origin of steroid acids. The origin of steroid acids during biodegradation in crude oil was observed for the first time. Molecular structures of these steroid acids reveal that they arose from steranes via bacterial oxidation of sidechain terminal methyl groups. Our results suggest that microbial activities indeed contribute to the formation of carboxyl groups on the eukaryotic steroid skeletons, and we believe steroid acids are a promising biomarker for both geomicrobial processes and ancient eukaryotic life in the rock record.