Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cyanide. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to recover copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.
Bacteria biooxidation is an oxidation process caused by microbes where the valuable metal remains in the solid phase. In this process, the metal remains in the solid phase and the liquid can be discarded. Bacterial oxidation is a biohydrometallurgical process developed for pre-cyanidation treatment of refractory gold ores or concentrates. The bacterial culture is a mixed culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans. The bacterial oxidation process comprises contacting refractory sulfide ROM ore or concentrate with a strain of the bacterial culture for a suitable treatment period under an optimum operating environment. The bacteria oxidise the sulfide minerals, thus liberating the occluded gold for subsequent recovery via cyanidation.
Acidithiobacillus is a genus of the Acidithiobacillia in the "Proteobacteria". The genus includes acidophilic organisms capable of iron and/or sulfur oxidation. Like all "Proteobacteria", Acidithiobacillus spp. are Gram-negative. They are also important generators of acid mine drainage, which is a major environmental problem around the world in mining.
Halothiobacillus is a genus in the Gammaproteobacteria. Both species are obligate aerobic bacteria; they require oxygen to grow. They are also halotolerant; they live in environments with high concentrations of salt or other solutes, but don't require them in order to grow.
Sulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen. The final product or these processes, sulfide, has a considerable influence on the chemistry of the environment and, in addition, is used as electron donor for a large variety of microbial metabolisms. Several types of bacteria and many non-methanogenic archaea can reduce sulfur. Microbial sulfur reduction was already shown in early studies, which highlighted the first proof of S0 reduction in a vibrioid bacterium from mud, with sulfur as electron acceptor and H2 as electron donor. The first pure cultured species of sulfur-reducing bacteria, Desulfuromonas acetoxidans, was discovered in 1976 and described by Pfennig Norbert and Biebel Hanno as an anaerobic sulfur-reducing and acetate-oxidizing bacterium, not able to reduce sulfate. Only few taxa are true sulfur-reducing bacteria, using sulfur reduction as the only or main catabolic reaction. Normally, they couple this reaction with the oxidation of acetate, succinate or other organic compounds. In general, sulfate-reducing bacteria are able to use both sulfate and elemental sulfur as electron acceptors. Thanks to its abundancy and thermodynamic stability, sulfate is the most studied electron acceptor for anaerobic respiration that involves sulfur compounds. Elemental sulfur, however, is very abundant and important, especially in deep-sea hydrothermal vents, hot springs and other extreme environments, making its isolation more difficult. Some bacteria – such as Proteus, Campylobacter, Pseudomonas and Salmonella – have the ability to reduce sulfur, but can also use oxygen and other terminal electron acceptors.
Iron-oxidizing bacteria are chemotrophic bacteria that derive energy by oxidizing dissolved ferrous iron. They are known to grow and proliferate in waters containing iron concentrations as low as 0.1 mg/L. However, at least 0.3 ppm of dissolved oxygen is needed to carry out the oxidation.
Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC) or biocorrosion, is "corrosion affected by the presence or activity of microorganisms in biofilms on the surface of the corroding material." This corroding material can be either a metal or a nonmetal.
Lithotrophs are a diverse group of organisms using an inorganic substrate to obtain reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic respiration. While lithotrophs in the broader sense include photolithotrophs like plants, chemolithotrophs are exclusively microorganisms; no known macrofauna possesses the ability to use inorganic compounds as electron sources. Macrofauna and lithotrophs can form symbiotic relationships, in which case the lithotrophs are called "prokaryotic symbionts". An example of this is chemolithotrophic bacteria in giant tube worms or plastids, which are organelles within plant cells that may have evolved from photolithotrophic cyanobacteria-like organisms. Chemolithotrophs belong to the domains Bacteria and Archaea. The term "lithotroph" was created from the Greek terms 'lithos' (rock) and 'troph' (consumer), meaning "eaters of rock". Many but not all lithoautotrophs are extremophiles.
Beggiatoa is a genus of Gammaproteobacteria belonging the order Thiotrichales, in the Proteobacteria phylum. This genus was one of the first bacteria discovered by Russian botanist Sergei Winogradsky. During his research in Anton de Bary’s laboratory of botany in 1887, he found that Beggiatoa oxidized hydrogen sulfide (H2S) as energy source, forming intracellular sulfur droplets, oxygen is the terminal electron acceptor and CO2 is used as carbon source. Winogradsky named it in honor of the Italian doctor and botanist Francesco Secondo Beggiato. Winogradsky referred to this form of metabolism as "inorgoxidation" (oxidation of inorganic compounds), today called chemolithotrophy. These organisms live in sulfur-rich environments such as soil, both marine and freshwater, in the deep sea hydrothermal vents and in polluted marine environments. The finding represented the first discovery of lithotrophy. Two species of Beggiatoa have been formally described: the type species Beggiatoa alba and Beggiatoa leptomitoformis, the latter of which was only published in 2017. This colorless and filamentous bacterium, sometimes in association with other sulfur bacteria (for example the genus Thiothrix), can be arranged in biofilm visible at naked eye formed by very long white filamentous mate, the white color is due to the stored sulfur. Species of Beggiatoa have cells up to 200 µ in diameter and they are one of the largest prokaryotes on Earth.
Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.
Biomining is the technique of extracting metals from ores and other solid materials typically using prokaryotes, fungi or plants. These organisms secrete different organic compounds that chelate metals from the environment and bring it back to the cell where they are typically used to coordinate electrons. It was discovered in the mid 1900s that microorganisms use metals in the cell. Some microbes can use stable metals such as iron, copper, zinc, and gold as well as unstable atoms such as uranium and thorium. Companies can now grow large chemostats of microbes that are leaching metals from their media, these vats of culture can then be transformed into many marketable metal compounds. Biomining is an environmentally friendly technique compared to typical mining. Mining releases many pollutants while the only chemicals released from biomining is any metabolites or gasses that the bacteria secrete. The same concept can be used for bioremediation models. Bacteria can be inoculated into environments contaminated with metals, oils, or other toxic compounds. The bacteria can clean the environment by absorbing these toxic compounds to create energy in the cell. Microbes can achieve things at a chemical level that could never be done by humans. Bacteria can mine for metals, clean oil spills, purify gold, and use radioactive elements for energy.
Hydrogen oxidizing bacteria are a group of facultative autotrophs that can use hydrogen as an electron donor.
Thiosulfate dehydrogenase is an enzyme that catalyzes the chemical reaction:
An enzymatic biofuel cell is a specific type of fuel cell that uses enzymes as a catalyst to oxidize its fuel, rather than precious metals. Enzymatic biofuel cells, while currently confined to research facilities, are widely prized for the promise they hold in terms of their relatively inexpensive components and fuels, as well as a potential power source for bionic implants.
The outflow of acidic liquids and other pollutants from mines is often catalysed by acid-loving microorganisms; these are the acidophiles in acid mine drainage.
Rusticyanin (RCN) is a copper protein with a type I copper center that plays an integral role in electron transfer. It can be extracted from the periplasm of the gram-negative bacterium Thiobacillus ferrooxidans, also known as Acidithiobacillus ferrooxidans. Rusticyanin is also found in the membrane-bound form in the surface of T. ferrooxidans. It is a part of an electron transfer chain for Fe(II) oxidation.
Iron:rusticyanin reductase is an enzyme with systematic name Fe(II):rusticyanin oxidoreductase. This enzyme catalyses the following chemical reaction
An electrolithoautotroph is an organism which feeds on electricity. These organisms use electricity to convert carbon dioxide to organic matters by using electrons directly taken from solid-inorganic electron donors. Electrolithoautotrophs are microorganisms which are found in the deep crevices of the ocean. The warm, mineral-rich environment provides a rich source of nutrients. The electron source for carbon assimilation from diffusible Fe2+ ions to an electrode under the condition that electrical current is the only source of energy and electrons. Electrolithoautotrophs form a third metabolic pathway compared to photosynthesis (plants converting light into sugar) and chemosynthesis (animals consuming food).
Acidithrix ferrooxidans is a heterotrophic, acidophilic and Gram-positive bacterium from the genus of Acidithrix. The type strain of this species, A. ferrooxidans Py-F3 was isolated from an acidic stream draining from a copper mine in Wales. This species grows in a variety of acidic environments such as streams, mines or geothermal sites. Mine lakes with a redoxcline support growth with ferrous iron as the electron donor. A. ferrooxidans grows rapidly in macroscopic streamer, producing greater cell densities than other streamer-forming microbes. Use in a bioreactors to remediate mine waste has been proposed due to cell densities and rapid oxidation of ferrous iron oxidation in acidic mine drainage. Exopolysaccharide production during metal substrate metabolism, such as iron oxidation helps to prevent cell encrustation by minerals.
Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of energy-rich oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).
