DFG-funded project (BL 971/1-1 and follow-up project BL 971/1-2): Biosynthesis and geochemical fate of bacterial hopanoids in anoxic environments

Principal investigator: Dr. M. Blumenberg

Concentrations and distributions of non-extended and extended hopanoids (bacteriohopanepolyols) in the upper Black Sea sediments were studied with respect to sources and changes during the Holocene. Interestingly, the distribution of bacterial BHP sources did not change remarkably during the shift from lacustrine to marine conditions after the first spills of Mediterranean sea water via the Bosporus. Moreover, an increase in BHP production at the end of the lacustrine stage mirror enhanced paleoproductivity in the euphotic zone at that time, most likely as a result of a shift in the N/P-regime (Blumenberg et al., 2009; GCA).

More than 40 strains of aerobic, marine bacteria were screened for the production of bacteriohopanepolyols by LC-MS. Our work supports other studies (e.g. Pearson et al., 2007, 2009) demonstrating a much lower distribution of BHPs in bacteria than previously suggested (e.g. Rohmer et al., 1984). However, in the frame of the project a suite of anaerobic, sulfate-reducing, Desulfovibrio were studied for hopanoids. In most of these bacteria hopanoids lacked. However, Desulfovibrio bastinii isolated from oil-field formation water were demonstrated to contain various BHPs (Blumenberg et al., 2009; FEMS Microb. Lett.), which indicates that BHP production in this δ-proteobacterial subgroup is widespread and not restricted to previously known members (Blumenberg et al., 2006). 

Overview of the project

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 2.77 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 anaerobic bacteria in the geological hopanoid-record and also the geochemical fate of hopanoids in anoxic settings are still unclear.
Major objectives of this project are to

  • determine the capability of still non-investigated anaerobic (and aerobic) bacteria of synthesising hopanoids,
  • identify hopanoid producing bacteria in anaerobically formed, methane fuelled microbial Black Sea mats, and to
  • characterise the fate and structural modifications of allochthonous and autochthonous bacteriohopanepolyols (BHPs) during early diagenesis in anoxic sediments (i.e. the Black Sea).

An excellent place to study different microbial processes and the impact on marine sediments is the Black Sea. Here in anaerobic, dysaerobic and aerobic bacteria thrive in various water depths and, moreover, changed remarkably through the Holocene.

In the recent running period (BL 971/1-2) the work is mainly focused on the distribution of sedimentary geo- and biohopanoids in a highly productive upwelling area (Benguela; Blumenberg et al., in revision). Moreover, in cooperation with Martin Krüger (BGR, Hannover) in vitro experiments will be designed in order to get information on the role of hopanoids. These approaches shall compare hopanoid production under various nitrogen and oxygen preconditions.

For further details or paper requests please contact Martin Blumenberg.

contact:

martin.blumenberg@geo.uni-goettingen.de