2014 Annual Science Report

University of Wisconsin Reporting  |  SEP 2013 – DEC 2014

Project 2A: The Catalysis Effect of Extracellular Polymeric Substances Excreted by Fermentative Bacteria on Ca-Mg Carbonate Precipitation

Project Summary

Experiments show that purified non-metabolizing biomass from pure cultures of both anaerobic fermenting and sulfate-reducing bacteria closely related to those organisms present in the consortium could also catalyze the precipitation of disordered dolomite. Polysaccharides that are the dominant components in the EPS act as catalysts for weakening surface water and Mg (II) boning and enhancing dolomite crystallization. Our study contributes to the understanding of the “dolomite problem” by revealing (1) the catalytic effect of bound EPS on Ca-Mg carbonate crystallization and (2) the possible involvement of anaerobic fermenting bacteria in sedimentary dolomite formation, which has not been reported previously.

4 Institutions
3 Teams
1 Publication
0 Field Sites
Field Sites

Project Progress

Because of its rare occurrence in modern sediments, as well as the difficulty in synthesizing it under low-temperature conditions in the laboratory, the origin of sedimentary dolomite has remained a long-standing enigma, often referred to as the “dolomite problem.” Recently, anaerobic microorganisms, such as sulfate-reducing bacteria and methanogens, have been recognized for mediating dolomite precipitation. However, the exact role of microorganisms in dolomite crystallization is still under debate and the possible involvement of anaerobic fermenting bacteria has not been studied. In our early studies, we characterized the effect of purified non-metabolizing biomass and bound extracellular polymeric substances (EPS) of a natural consortium of anaerobic microorganisms dominated by fermenting bacteria and sulfate-reducing bacteria on Ca-Mg carbonate precipitation. Our data show that disordered dolomite, a precursor of some sedimentary stoichiometric ordered dolomite, can be precipitated in calcite-seeded Ca-Mg carbonate solutions containing purified non-metabolizing consortium biomass. Bound EPS extracted from the consortium culture were shown to be the active component that triggered the crystallization of disordered dolomite. Recent experiments show that purified non-metabolizing biomass from pure cultures of both anaerobic fermenting and sulfate-reducing bacteria closely related to those organisms present in the consortium could also catalyze the precipitation of disordered dolomite (Figs. 1, 2).

Figure 1
Comparison of the MgCO3 contents of synthetic carbonates precipitated in control, non-metabolizing H. saccharolyticum or D. retbaense biomass-bearing solutions at different initial Mg:Ca ratios.
SEM images of synthetic carbonates. (a) SEM image of synthetic rhombohedral calcite seeds. (b) SEM image of high-Mg calcite clusters (~12 mol% MgCO3) synthesized in control solutions containing synthetic seeds. (c) SEM image of disordered Mg-rich dolomite (~57 mol% MgCO3) synthesized in experimental solutions containing non-metabolizing H. saccharolyticum biomass and synthetic seeds. Disordered dolomite overgrew synthetic seeds, and the rhombohedral shape was overall preserved. (d) A close up of the image in c shows that disordered dolomite occurred as extremely small nano-crystals.

It is proposed that polysaccharides that are the dominant components in the EPS act as catalysts for lowering surface water and Mg (II) boning and enhance dolomite crystallization. Future ab initio simulations based on density functional theory (DFT) will be carried out in order to understand the catalytic roles of EPS in sedimentary dolomite crystallization.

This study defines a plausible role of anaerobic ferment¬ing bacteria in sedimentary dolomite formation, which to our best knowledge has not been reported previously. Unlike SRB, which are limited to environments with high concentrations of dissolved sulfate, the ubiquitous distribution of anaerobic fermenting bacteria in both freshwater and marine environments may extend the range of natural environments where microbial-induced dolomite precipitation could take place.

  • PROJECT INVESTIGATORS:
  • PROJECT MEMBERS:
    Huifang Xu
    Project Investigator

    Eric Roden
    Co-Investigator

    Evgenya Shelobolina
    Collaborator

    Zhizhang Shen
    Collaborator

    Fangfu Zhang
    Collaborator

  • RELATED OBJECTIVES:
    Objective 7.1
    Biosignatures to be sought in Solar System materials

    Objective 7.2
    Biosignatures to be sought in nearby planetary systems