Intracellular metal pumping in microbial excavation by microbes

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Cyanobacteria are among the most common, widespread and environmentally significant agents of bio-erosion, boring microscopic galleries as they grow within carbonate substrates. The mechanisms by which they achieve this against chemical equilibrium are poorly known. Our work showed that boring is likely driven by the action of membrane-bound Ca2+ transporting ATPases, powered directly by photosynthetically derived ATP, acting to maintain the levels of free Ca2+ in the interstitial space of the distal borehole very low, a situation that promotes local calcite dissolution, with Ca2+ then travelling intra-cellularly down a concentration gradient in the filament to be released into the outside medium. We intend here to advance our understanding of the boring mechanism at the molecular, genetic and cellular level and to test its universality, by probing its variability in essence or detail with respect to microbial agents other than the models previously used, and for mineral substrates other than CaCO3. We will achieve this through genetic and cellular characterization of the Ca2+ transport systems, molecular biology techniques and micro-imaging techniques based on confocal microscopy of model microbes. We will also interrogate natural complex communities of boring microorganims from a variety of geographic and mineralogical settings (limestones, dolostones and biogenic carbonates) for their compliance with the Ca2+-transport mechanism. Finally, renewed efforts of cultivation will be used to address the mysterious excavation of phosphates, dolomite, and magnesite, a capacity that model microbes lacks, but is assumed to take place in nature. Moving from descriptive to mechanistic models of understanding, as this work will attempt, remains one of the frontiers of geobiology. The research will attempt to ascertain the exact mechanisms by which microbes can use the energy from the sun to power dissolving minerals like limestone, when geochemistry would predict they should not dissolve at all. This knowledge would offer the potential to explain several biological and geological phenomena of widespread importance. For example, it will involve the study of physiology of calcium transport, the same phenomenon that drives muscle movement in humans, in a very different setting. It may also contribute to our ability to predict the consequences of global acidification of the oceans with respect to coastal limestone dissolution. It will contribute basic knowledge with potential applications in biomaterial science, potentially even providing a means for combating calcification in engineered systems, or for deterring the bio-deterioration of buildings and monuments. The research will be intricately embedded with activities in education, training, dissemination and outreach.