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Vent Fluid Chemistry and the Microbial Habitat |
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Vent Fluid Chemistry and the Microbial Habitat Because microbial metabolism must derive energy by mediating thermodynamically favorable chemical reactions, it is axiomatic that the chemical and physical environment will have a direct impact on the type of organisms that can exist there. In an oversimplified view, favorable conditions for microbial growth in hydrothermal systems depend on the confluence of electron donors (reduced compounds derived from high-temperature water-rock interaction) and electron acceptors (more oxidized compounds present in seawater or interstitial water flowing below the seafloor) within a temperature range that is tolerable to microorganisms. This temperature range extends up to at least 110°C. Some of the reactions that microbes can mediate in submarine hydrothermal systems are shown in Figure 6, from Butterfield et al. 1997. Conditions below the sea floor in hydrothermal systems are ripe for microbial production. It is very likely that different types of fluid chemistry will give rise to different microbial populations, but very little work has been done on this in submarine hydrothermal systems. The figure above depicts chemical and microbial processes in a diffuse upflow zone. Injection of a magma dike results in delivery of reduced volatile compounds and metals through outgassing and water-rock interaction. Phase separation partitions volatiles and some metals into the vapor phase, and brines accumulate around heat source. The thermal and redox gradient provides a zone for chemical and microbial oxidation of reduced gases and metals as circulating seawater is entrained (microbial methanogenesis and sulfur reduction are known to occur at 110 C). (From Figure 6, Butterfield et al. 1997, Philosophical Transaction of the Royal Society, vol 355.)
For more information on this topic, the following papers are recommended as a starting point: Jannasch, H. W. 1995 Microbial interaction with hydrothermal fluids. In Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions (ed. S. E. Humphris et al.), pp. 273-296. Washington D.C.: American Geophysical Union. Karl, D. M. 1995 Ecology of free-living, hydrothermal vent microbial communities. In The Microbiology of Deep-Sea Hydrothermal Vents (ed. D. M. Karl), pp. 35-125. Boca Raton: CRC Press. D. A. Butterfield, I. R. Jonasson, G. J. Massoth, R. A. Feely, K.K. Roe, R. E. Embley, J. F. Holden, R. E. McDuff, M. D. Lilley, and J. R. Delaney 1997 Seafloor eruptions and evolution of hydrothermal fluid chemistry. Phil. Trans. R. Soc. Lond. A., 355, 369-386.
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