Biosynthesis and geochemical fate of bacterial hopanoids in anoxic environments
Zusammenfassung der Projektergebnisse
The project "Biosynthesis and geochemical fate of bacterial hopanoids in anoxic environments and paleo-environmental implications" focused on a better understanding of the origin, the biogeochemical controls on their production, and the cycling of a widespread compound class, hopanoids, in anoxic sediments and rocks. Extended hopanoids are pentacyclic molecules with a side chain in cell lipids and are solely produced by distinct bacterial groups. Unless almost 40 years of hopanoid research, major bacterial contributors of hopanoids in sediments have still to be identified. Of special interest in this project are bacteria, which live in oxygen-free settings. Respective bacteria were long thought to lack hopanoids, but in the frame of this project it was found that widespread sulfate-reducing bacteria (SRB) are indeed able to produce hopanoids in partially high amounts. One aim of the project was to identify hopanoid-producing SRB and to get knowledge on how much SRB contribute to the hopanoid inventory in recent and ancient geological settings. Organic geochemical data identified two widespread SRB, "Desulfovibrio zoosterae" and "D. salexigens", as yet unknown hopanoid-producing bacteria. Moreover, a genetic survey demonstrates that the key enzymes necessary for hopanoid production are also present in other SRB. The potential for SRB as hopanoid sources in anoxic settings was shown, but their actual relevance in different geological settings has still to be verified. However, suboxic zones in stratified water columns but also a massive microbial mat from Kiritimati were recognized as the main areas where hopanoid production occurs. Another aim of the project was to identify the role of hopanoids in bacteria and thus, the biogeochemical conditions favoring production of these structures (or growth of hopanoid producing bacteria). One hypothesis is the existence of a relationship between hopanoids and the capability of bacteria to fix atmospheric nitrogen (a process only occurring in nitrogen depleted settings). Strong evidence for this link and, hence, the applicability of hopanoids to indicate nitrogen limitation was found. In various geological settings, in Holocene Central Baltic Sea sediments, shallow water sediments deposited during the Cretaceous, and black shales from a 1.1 billion year old Precambrian sedimentary succession, hopanoids were particularly abundant. The respective periods obviously are characterized by the prevalence of bacteria and biogeochemical scenarios for the time intervals suggests a crucial role of hopanoid producing bacteria in nitrogen fixation. As the currently third-oldest undoubted record of hydrocarbon biomarkers from the Precambrian, it was recognized in the frame of the project that bacteria and not algae were key players in the studied setting. These findings are an important support for models suggesting nitrogen-limitation during most times of the Proterozoic and that this suppressed algal growth and the development of higher life. In addition to the biogeochemical clues encoded in hopanoid occurrences, the diagenetical turnover and preservation in anoxic sediments were intensively studied by the use of catalytic hydropyrolysis (HyPy). Different settings up to an age of the Mesoproterozoic were studied, and the applicability of HyPy for the study of macromolecular linked hopanoids was clearly demonstrated. With HyPy it was shown that even at the earliest stages of anoxic diagenesis abundances of hopanoids in the non-extractable organic matter (of Holocene Baltic Sea sediments) may exceed the amounts of extractable intact bacteriohopanepolyols. Oxygen limited conditions are thus not only crucial for hopanoid production but also for the transfer of these compounds from the bio- to the geosphere.
Projektbezogene Publikationen (Auswahl)
- Algen vor einer Milliarde Jahren weniger verbreitet als angenommen: Göttinger Forscher untersuchen Leben in erdgeschichtlich frühen Ozeanen. Presseinformation der Universität Göttingen, Nr. 3/2012 - 13.01.2012
- Biomarkers of black shales formed by microbial mats, Late Mesoproterozoic (1.1 Ga) Taoudeni Basin, Mauritania.
Precambrian Research, Vol. 196–197. 2012, pp. 113–127.
Blumenberg, M., Thiel, V., Riegel, W., Kah, L.C., Reitner, J.
(Siehe online unter https://doi.org/10.1016/j.precamres.2011.11.010) - Imbalanced nutrients as triggers for black shale formation in a shallow shelf setting during the OAE 2 (Wunstorf, Germany) Biogeosciences, Vol. 9. 2012, Issue 10, pp. 4139-4153.
Blumenberg, M. and Wiese, F.
(Siehe online unter https://doi.org/10.5194/bg-9-4139-2012) - Novel findings on hopanoid occurrences among sulfate reducing bacteria: is there a direct link to nitrogen fixation?
Organic Geochemistry, Vol. 49. 2012, pp. 1–5.
Blumenberg, M., Hoppert, M., Krüger, M., Dreier, A., Thiel, V.
(Siehe online unter https://doi.org/10.1016/j.orggeochem.2012.05.003) - Bacteriohopanepolyols in a stratified cyanobacterial mat from Kiritimati (Christmas Island, Kiribati). Organic Geochemistry, Vol. 55. 2013, pp. 55–62.
Blumenberg, M., Arp, G., Reitner, J., Schneider, D., Thiel, V.
(Siehe online unter https://doi.org/10.1016/j.orggeochem.2012.11.004) - Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the Central Baltic Sea. Biogeosciences, Vol. 10.2013, issue 4, pp. 2725- 2735
Blumenberg, M., Berndmeyer, C., Moros, M., Schmale, O., Thiel, V.
(Siehe online unter https://doi.org/10.5194/bg-10-2725-2013) - Biomarkers for aerobic methanotrophy in the water column of the stratified Gotland Deep (Baltic Sea). Organic Geochemistry, Vol. 55. 2013, pp. 103–111.
Berndmeyer, C., Thiel, V., Schmale, O., Blumenberg, M.
(Siehe online unter https://doi.org/10.1016/j.orggeochem.2012.11.010)
