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Abstract Eukaryotes produce highly modified sterols, including cholesterol, essential to eukaryotic physiology. Although few bacterial species are known to produce sterols, de novo production of cholesterol or other complex sterols in bacteria has not been reported. Here, we show that the marine myxobacteriumEnhygromyxa salinaproduces cholesterol and provide evidence for further downstream modifications. Through bioinformatic analysis we identify a putative cholesterol biosynthesis pathway inE. salinalargely homologous to the eukaryotic pathway. However, experimental evidence indicates that complete demethylation at C-4 occurs through unique bacterial proteins, distinguishing bacterial and eukaryotic cholesterol biosynthesis. Additionally, proteins from the cyanobacteriumCalothrixsp. NIES-4105 are also capable of fully demethylating sterols at the C-4 position, suggesting complex sterol biosynthesis may be found in other bacterial phyla. Our results reveal an unappreciated complexity in bacterial sterol production that rivals eukaryotes and highlight the complicated evolutionary relationship between sterol biosynthesis in the bacterial and eukaryotic domains.
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Analysis of Sterol Diagenesis Stages in a Peat Core from Kamchatka, Russia
Peatlands are a critical part of the global carbon cycle. While many studies of peat carbon focus on accumulation, less is known about peat decay. We use the diagenesis of sterols to track the decomposition of peat in a Holocene-length core of a sedge fen on the Kamchatka Peninsula, Russia. Diagenesis can transform sterols as soon as the peat is initially deposited, but they can also remain unchanged for millennia. We have quantified the transformation of sterols into their diagenetic products to measure the maturity of peat and estimate carbon loss. Further, there are two pathways in sterol diagenesis, oxidative and reductive, and the products of these two pathways can indicate the conditions under which the peat degraded. This project focuses on the transformations of cholesterol, campasterol, and β- sitosterol, to cholestanol, campastanol, and stigmasta-3,5-diene-7-one, respectively. During the late Glacial period (before 10 ka) the oxidative pathway dominated sedimentary sterol transformation, indicating strongly reducing conditions. These sediments were deposited before the site transitioned to a peatland, and are dominated by sapropel, supporting the steroid evidence for reducing conditions. During the Early Holocene, (about 8 -6 ka) sterols, and, presumably, peat, were well preserved, and coincided with high carbon accumulation rates. In the middle Holocene (5 – 2 ka) the reductive diagenetic pathway dominated, indicating oxidizing conditions, and coincided with low rates of C accumulation. At 2.5 ka, conditions favoring the preservation of sterols returned, along with higher C accumulation.
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- Award ID(s):
- 1757602
- PAR ID:
- 10091131
- Date Published:
- Journal Name:
- American Geophysical Union, Fall Meeting 2018, abstract #PP23A-05
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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