Mechanisms of Carbonate Dissolution By Boring Cyanobacteria

在生物与矿物世界之间的许多相互作用中，从生物膜的微尺度钙化到珊瑚环礁的增生，碳酸盐的形成和破坏是最明显和最广泛的相互作用之一。生物成因碳酸盐沉淀一直是人们关注的焦点，但其溶解也可以由生物，特别是微生物介导。真菌、微藻和蓝藻活跃地钻入钙质基质中，人们已经知道了一个多世纪，自前寒武纪以来，它们就留下了化石和化石痕迹。这些无聊的微生物与各种地质现象密切相关，包括海岸石灰石的侵蚀形态形成、珊瑚礁的破坏、碳质砂的改造和叠层石的胶结。但是，尽管它们具有重要意义，但它们能够以受控的方式挖掘碳酸盐的机制仍有待研究。关于它们的作用机制，最普遍的假设是它们通过排泄酸来溶解石灰石。然而，我们认为，就像蓝藻这样的光合生物而言，它们的活动构成了一个明显的悖论，因为碳酸盐的溶解与众所周知的含氧光合代谢的地微生物效应相反，后者往往会使周围介质呈碱性，从而促进钙化，而不是碳酸盐的溶解。有人可以说无聊的蓝藻很有趣。我们将测试三种替代模型，这些模型可以解释蓝藻无聊，并且仍然与热力学，生理和矿物学限制相一致。有两种模型是基于光合作用和呼吸活动的分离（时间上或空间上）。第三种模型是基于局部和定向细胞钙运输。我们将采用三层实验方法，使用培养的微生物和具有良好特征的矿物基质，这将为每个模型的有效性提供证据。我们将使用：a)长期监测各种环境参数的生长和钻孔速度，b)短期研究主动钻孔系统中的微尺度传质，包括特定抑制剂的影响，使用微传感器，以及c)提供视觉和微观化学信息的活性矿物/微生物系统的高级显微镜研究：激光扫描共聚焦显微镜和二次离子质谱（SIMS）。该项目还包括重要的教育和外联活动。它呼吁为高中和K-12教育工作者开发地球微生物学材料，为公众建立一个网页，并参与每年的外展活动。

Among the many interactions between living organisms and the mineral world, the formation and destruction of carbonates stands as one of the most conspicuous and widespread, from microscale calcification in biofilms to the accretion of coralline atolls. Biogenic carbonate precipitation has received the most attention, but its dissolution can also be mediated by organisms, and by microorganisms in particular. Fungi, microalgae and cyanobacteria that actively bore into calcareous substrates have been known for more than a century, and have been leaving fossils and trace fossils since the Precambrian. These boring microorganisms are centrally implicated in a variety of geological phenomena, ranging from the erosive morphogenesis of coastal limestones, the destruction of coral reefs, the reworking of carbonaceous sands and the cementation of stromatolites. But for all their significance, the mechanism by which they can excavate carbonates in a controlled manner remains to be studied. The most common hypothesis as to their action mechanisms has been that they dissolve limestone by excretion of acids. However, we contend that, in the case of photosynthetic organisms like cyanobacteria, their activity constitutes an apparent paradox, since the dissolution of carbonates runs contrary to the well-known geomicrobial effects of oxygenic photosynthetic metabolism, which will tend to make the surrounding medium alkaline and therefore promote calcification, not carbonate dissolution. One can say that boring cyanobacteria are intriguing. We will test three alternative models than can explain cyanobacterial boring and still be consistent with thermodynamic, physiological and mineralogical constraints. Two models are based on the separation of photosynthetic and respiratory activities (either temporally or spatially). The third model is based on localized and directed cellular calcium transport. We will undertake a three-tiered experimental approach using cultivated microorganisms and well characterized mineral substrates that should offer evidence regarding the validity of each of these models. We will use: a) long-term monitoring of the rates of growth and boring with manipulations of various environmental parameters, b) short-term studies of microscale mass transfer in actively boring systems, including the effects of specific inhibitors, using microsensors , and c) advance microscopy studies of active mineral /microbe systems that offer both visual and micro-chemical information: laser scanning confocal microscopy and secondary ion mass spectroscopy (SIMS). The project also entails significant educational and outreach activities. It calls for the development of geomicrobiology materials for High School and K-12 educators, a web page for the general public, and participation in yearly outreach activities.