It is widely accepted that microbe-carbonate interactions are biologically induced processes; however the participating agents are not well understood.  Here we attempt to probe these interactions by interrogating microbially mediated calcite dissolution and crystallization.  Six microbial isolated (3 bacteria, 3 fungi) were first tested in dissolution experiments and the results showed that the Ca release does not correspond well to the microbially induced pH change in the solutions; rather, it exhibits a strong correlation with the activity of carbonic anhydrase (CA) produced by different microorganisms, contradicting to the generally accepted theorem that acidity is the governing factor for calcite bioweathering.  This finding was further confirmed by crystallization experiments where only limited calcite nucleation occurred when the bacterial growth was limited by N, a condition leading to the excretion of large amount of extracellular polymeric substances (formation of thick capsules) and low CA activity.  Additional crystallization experiments carried out in the supernatant of cultural media, concentrated bacterial sludge, and the original culture found calcite formation in the presence of bacteria but a significant portion of co-precipitated vaterite in the supernatant.  Furthermore, our results revealed that the bacteria had a strong tendency to colonize the center area of the {104} calcite faces.  Morphological characteristics of calcite crystals formed in the original culture and concentrated bacterial media suggests that the bacterial colony might have promoted the growth normal to individual {104} faces when the cell concentration was high, but retarded it or even caused dissolution of the immediate substrate surfaces when the concentration was low.  d<sup>13</sup>C measurements showed the crystals were further enriched in the heavier carbon isotope, implying that the bacterial metabolism was not involved in the crystallization process, implying the biomineralization process is primarily promoted by epi- and inter-cellular growth.

Chemical and physical agents of microbe-carbonate interactions

251st National Meeting (2016)

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