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Having fun with rock-eating microbes!
Study of the mechanisms of carbonate dissolution by boring cyanobacteria
Our research focuses in the study of some curious microbes that affect us in a very particular way. We are talking about cyanobacteria that excavate or bore into the rocks or other substrates know as euendolithic cyanobacteria, or as we like to call them, boring cyanobacteria (I can guarantee you, there is nothing "boring" about them). Carbonate minerals like calcite or dolomite, and other carbonates like dead coral, carbonate sand, marble sculptures, fountains or even concrete represent some the preferred substrates for endolithic microbes. By choosing this niche they improve their chances of survival, and play both friend and foe in the environment taking an important role in the rock cycle, and sometimes accelerating the deterioration of monuments made of carbonates.
See also an example of past microborers.
Cyanobacteria are photosynthetic bacteria. They utilize the sun's radiant energy and transform it into chemical energy by the process of oxygenic photosynthesis. Boring cyanobacteria belong to a group of microbes classified as endoliths (from the Greek "endo" wich means within and "lithos" which means stone). There are various types of endoliths, including chasmolitic, cryptoendolithic and euendolithic microbes. Chasmolitic and cryptoendolithic microbes live in crevasses and cracks of rocks, utilizing this naturally available space as a refuge from damaging UV radiation, desiccation and grazing. But the stars of our research are the true endoliths or "euendoliths" that actually dissolve the rock matrix, boring into the substrate and making a tunnel where the cells spend their life. This biogenic destruction of carbonates contributes to erosion and the transformation of the mineral matrix into microcrystalline carbonate or micrite. The process is not always negative; in some microbial communities like in the case of stromatolites the micritization actually contributes to the growth of these structures by cementing sediments together, providing support. The fascinating thing about these boring microbes is that no one really knows how they do it.
Some researchers have suggested various mechanisms including mechanical destruction, dissolution by acid deposition and active transport of metal ions by ATP driven pumps, the later being our proposed mechanism of action.
Our current model, Fischerella sp. is a marine cyanobacteria isolated from the coast of Cabo Rojo, a coastal town in the island of Puerto Rico. This particular microbe dissolves calcium carbonate by a mechanism that is not well understood and the one our lab is currently investigating. Our group is focusing on the hypothesis of an ATP-driven calcium pump (see García-Pichel, 2006) and our approach includes using calcium-sensitive fluorescent dyes like Calcium Green and confocal microscopy to try to image the dissolution of calcite (crystalline calcium carbonate) in situ. Other techniques include the use of calcium pump blockers to evaluate the effect on the boring activity, as well as measuring boring activity in minerals other than calcite.
If you are interested in knowing more about this research, don't hesitate to contact us at the FGP lab.
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