Geomicrobiology

Geomicrobiology is the scientific field at the intersection of geology and microbiology. It concerns the effect of microbes on geological and geochemical processes and vice versa. Such interactions occur in the geosphere (rocks, minerals, soils, and sediments), the atmosphere and the hydrosphere. Applications include aquifers and public drinking water supplies. Geomicrobiology is the scientific field at the intersection of geology and microbiology. It concerns the effect of microbes on geological and geochemical processes and vice versa. Such interactions occur in the geosphere (rocks, minerals, soils, and sediments), the atmosphere and the hydrosphere. Applications include aquifers and public drinking water supplies. Microorganisms are known to impact aquifers by modifying their rates of dissolution. In the karstic Edwards Aquifer, microbes colonizing the aquifer surfaces enhance the dissolution rates of the host rock. In the oceanic crustal aquifer, the largest aquifer on Earth, microbial communities can impact ocean productivity, sea water chemistry as well as geochemical cycling throughout the geosphere. The mineral make-up of the rocks affects the composition and abundance of these subseafloor microbial communities present. Through bioremediation some microbes can aid in decontaminating freshwater resources in aquifers contaminated by waste products. Some bacteria use metal ions as their energy source. They convert (or chemically reduce) the dissolved metal ions from one electrical state to another. This reduction releases energy for the bacteria's use, and, as a side product, serves to concentrate the metals into what ultimately become ore deposits. Biohydrometallurgy or in situ mining is where low-grade ores may be attacked by well-studied microbial processes under controlled conditions to extract metals. Certain iron, copper, uranium and even gold ores are thought to have formed as the result of microbe action. Subsurface environments, like aquifers, are attractive locations when selecting repositories for nuclear waste, carbon dioxide (See carbon sequestration), or as artificial reservoirs for natural gas. Understanding microbial activity within the aquifer is important since it may interact with and effect the stability of the materials within the underground repository. Microbe-mineral interactions contribute to biofouling and microbially induced corrosion. Microbially induced corrosion of materials, such as carbon steel, have serious implications in the safe storage of radioactive waste within repositories and storage containers. Microbes are being studied and used to degrade organic and even nuclear waste pollution (see Deinococcus radiodurans) and assist in environmental cleanup. An application of geomicrobiology is bioleaching, the use of microbes to extract metals from mine waste. Microbial remediation is used in soils to remove contaminants and pollutants. Microbes play a key role in many biogeochemistry cycles and can effect a variety of soil properties, such as biotransformation of mineral and metal speciation, toxicity, mobility, mineral precipitation, and mineral dissolution. Microbes play a role in the immobilization and detoxification of a variety of elements, such as metals, radionuclides, sulfur and phosphorus, in the soil.Thirteen metals are considered priority pollutants (Sb, As, Be, Cd, Cr, Cu, Pb, Ni, Se, Ag, Tl, Zn, Hg). Soils and sediment act as sinks for metals which originate from both natural sources through rocks and minerals as well as anthropogenic sources through agriculture, industry, mining, waste disposal, among others. Many heavy metals, such as chromium (Cr), at low concentrations are essential micronutrients in the soil, however they can be toxic at higher concentrations. Heavy metals are added into soils through many anthropogenic sources such industry and/or fertilizers. Heavy metal interaction with microbes can increase or decrease the toxicity. Levels of chromium toxicity, mobility and bioavailability depend on oxidation states of chromium. Two of the most common chromium species are Cr(III) and Cr(VI). Cr(VI) is highly mobile, bioavailable and more toxic to flora and fauna, while Cr(III) is less toxic, more immobile and readily precipitates in soils with pH >6. Utilizing microbes to facilitate the transformation of Cr(VI) to Cr(III) is an environmentally friendly, low cost bioremediation technique to help mitigate toxicity in the environment. Another application of geomicrobiology is bioleaching, the use of microbes to extract metals from mine waste. For example, sulfate-reducing bacteria (SRB) produce H2S which precipitates metals as a metal sulfide. This process removed heavy metals from mine waste which is one of the major environmental issues associated with acid mine drainage (along with a low pH).