Biosynthesis and geochemical fate of bacterial hopanoids in anoxic environments

DFG-funded project (2007-2013; current grant BL 971/1-3)

Principal investigator: Dr. Martin Blumenberg

Bacteriogenic hopanoids (bacteriohopanepolyols; BHPs) are widely distributed high-molecular weight components, found in about 50% of bacterial isolates analysed so far, and account for the ubiquity of their diagenetical products, the geohopanoids. Hopanoids with a likely bacterial origin have a geological record of more than 2 billion years. Until recently it was thought that the biosynthesis of hopanoids is restricted to aerobic bacteria and therefore occurrences in recent and fossil samples are used as indication for an oxygenated milieu. However, few recent studies showed that anaerobic bacteria are indeed capable of producing hopanoids (Sinninghe Damsté et al., 2004; Fischer et al., 2005; Härtner et al., 2005; Blumenberg et al., 2006). Nevertheless, the importance of these and yet unknown bacteria in the geological hopanoids record, the geochemical fate of hopanoids in anoxic settings, and the palaeoenvironmental implications are still rarely understood.

Therefore, the project aims at revealing information on

(i) which and how much bacteriohopanepolyols (BHPs) are synthesised by marine bacteria in specific anoxic environments, who are the producers and what are the palaeoenvironmental implications,
(ii) how much and by which mechanisms are BHPs fixed in anoxic sediments and
(iii) how important are these processes for the conservation of organic carbon in anoxic sedimentary environments?.


In the current, third phase (Dec. 2010 to Dec. 2013) focus will be laid on the function of hopanoids in bacteria and the paleoenvironmental implications of sedimentary BHPs variations (distributions and concentrations) on the biogeochemical setting in the overlying water column(s). The study of sources and fate of BHPs in two different marine systems (Black Sea and Benguela Upwelling System) during the first project period suggests that increased abundances of sedimentary BHPs were linked to low nitrogen status, favouring hopanoids-producing bacteria. For this purpose, the Baltic Sea is used as model system, a brackish/marine setting with considerable but heterogeneous recent and past N2-fixation activities and extraordinary high amounts of BHPs (see figure).
Furthermore, hopanoids will be also studied in much older samples to get information on the biogeochemical regimes during deposition (Cretaceous and Jurassic black shales; Neoproterozoic Cap carbonates). Here, the focus is laid on hopanoids, which are incorporated in kerogen to minimize problems of cross contamination from hopanoids in mobile bitumen. This will be accomplished by catalytic hydropyrolysis (HyPy); a powerful method, which quantitatively and qualitatively releases indigenous biomarkers that are obscured in geomacromolecular organic matter.




Figure: Concentrations and compositions and potential sources of BHPs in various marine surface sediments. Highest amounts were found in sediments from a deep basin of the Baltic Sea, where in the overlying waters high rates of nitrogen fixation have been reported (Blumenberg et al., 2009; 2010; unpublished).

Publications of the previous project period

Blumenberg, M., Krüger, M., Nauhaus, K., Talbot, H. M., Oppermann, B., Seifert, R., Pape, T., and Michaelis, W., 2006. Biosynthesis of hopanoids by sulfate-reducing bacteria (genus Desulfovibrio). Environ. Microbiol. 8, 1220-1227.

Blumenberg, M., Mollenhauer, G., Zabel, M., Reimer, A., and Thiel, V., 2010. Decoupling of bio- and geohopanoids in sediments of the Benguela Upwelling System (BUS). Organic Geochemistry 41, 1119-1129.

Blumenberg, M., Oppermann, B., Guyoneaud, R., and Michaelis, W., 2009a. Hopanoid-production by Desulfovibrio bastinii isolated from oilfield formation water. FEMS Microbiol. Lett. 293, 73-78.

Blumenberg, M., Seifert, R., Kasten, S., Bahlmann, E., and Michaelis, W., 2009b. Euphotic zone bacterioplankton sources major sedimentary bacteriohopanepolyols in the Holocene Black Sea. Geochimica et Cosmochimica Acta 73, 750-766.

Blumenberg, M., Seifert, R., and Michaelis, W., 2007. Aerobic methanotrophy in the oxic-anoxic transition zone of the Black Sea water column. Organic Geochemistry 38, 84-91.

Krüger, M., Blumenberg, M., Kasten, S., Wieland, A., Kanel, L., Klock, J.-H., Michaelis, W., and Seifert, R., 2008. A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black Sea. Environ. Microbiol. 10, 1934-1947.

 



For further details or paper requests please contact Martin Blumenberg.

contact:
martin.blumenberg@bgr.de