''Acidithiobacillus'' is a genus of the ''

Acidithiobacillia Acidithiobacillia is a class of the "''Pseudomonadota''". Its type order, the '' Acidithiobacillales'', was formerly classified within the ''Gammaproteobacteria'', and comprises two families of sulfur-oxidising autotroph An autotroph or prim ...

'' in the " Pseudomonadota". The genus includes acidophilic organisms capable of iron and/or sulfur oxidation. Like all ''"Pseudomonadota"'', ''Acidithiobacillus'' spp. are

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

. They are also important generators of

acid mine drainage Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines or coal mines. Acid rock drainage occurs naturally within some environments as part of the rock weathering ...

, which is a major environmental problem around the world in

mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...

Genus ''Acidithiobacillus''

''Acidithiobacillus'' are acidophilic obligate autotrophs (''Acidithiobacillus caldus'' can also grow mixotrophically) that use elementary sulfur, tetrathionate and ferrous iron as electron donors. They assimilate carbon from carbon dioxide using the transaldolase variant of the Calvin-Benson-Bassham cycle. The genus comprises motile, rod-shaped cells that can be isolated from low pH environments including low pH microenvironments on otherwise neutral mineral grains.

Phylogeny

The order

Acidithiobacillales The Acidithiobacillales are an order of bacteria within the class ''Acidithiobacillia'' and comprises the genera ''Acidithiobacillus'' and ''Thermithiobacillus''. Originally, both were included in the genus ''Thiobacillus'', but they are not rela ...

(i.e. ''Thermithiobacillus'') were formerly members of the ''Gammaproteobacteria'', with considerable debate regarding their position and that they could also fall within the ''Betaproteobacteria'', but the situation was resolved by whole-genome alignment studies and both genera have been reclassified to the new class ''Acidithiobacillia''. Some members of this genus were classified as ''

Thiobacillus ''Thiobacillus'' is a genus of Gram-negative Betaproteobacteria. ''Thiobacillus thioparus'' is the type species of the genus, and the type strain thereof is the StarkeyT strain, isolated by Robert Starkey in the 1930s from a field at Rutgers Un ...

'' spp., before they were reclassified in 2000. * ''Acidithiobacillus ferrooxidans'' (basonym ''Thiobacillus ferrooxidans'') can be isolated from iron-sulfur minerals such as

pyrite The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral. Pyrite's metallic luster and pale brass-yellow hue giv ...

deposits, oxidising

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

and sulfur as energy sources to support

autotrophic An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

growth and producing

ferric In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjective ferric or the prefix ferri- is often used to sp ...

iron and sulfuric acid. * ''Acidithiobacillus thiooxidans'' (basonym ''Thiobacillus thiooxidans'', ''Thiobacillus concretivorus'') oxidises sulfur and produces sulfuric acid; first isolated from the soil, it has also been observed causing

biogenic sulfide corrosion Biogenic sulfide corrosion is a bacterially mediated process of forming hydrogen sulfide gas and the subsequent conversion to sulfuric acid that attacks concrete and steel within wastewater environments. The hydrogen sulfide gas is biochemically ox ...

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...

sewer pipes by altering hydrogen sulfide in sewage gas into sulfuric acid.

Bioleaching

Species within ''Acidothiobacillus'' are used in the

biohydrometallurgy Biohydrometallurgy is a technique in the world of metallurgy that utilizes biological agents (bacteria) to recover and treat metals such as copper. Modern biohydrometallurgy advances started with the bioleaching of copper more efficiently in the 195 ...

industry in methods called

bioleaching 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 ...

and

biomining Biomining is the technique of extracting metals from ores and other solid materials typically using prokaryotes, fungi or plants (phytoextraction also known as phytomining or biomining). These organisms secrete different organic compounds that ...

, whereby metals are extracted from their ores through bacterial

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

. Biomining uses radioactive waste as an ore with the bacteria to obtain gold, platinum, polonium, radon, radium, uranium, neptunium, americium, nickel, manganese, bromine, mercury, and their isotopes. ''Acidithiobacillus ferrooxidans'' has emerged as an economically significant bacterium in the field of

, in the leaching of sulfide ores since its discovery in 1950 by Colmer, Temple and Hinkle. The discovery of ''A. ferrooxidans'' led to the development of “

”, which deals with all aspects of microbial mediated extraction of metals from minerals or solid wastes and acid mine drainage. ''A. ferrooxidans'' has been proven as a potent leaching organism, for dissolution of metals from low-grade sulfide ores. Recently, the attention has been focused upon the treatment of mineral concentrates, as well as complex sulfide ores using batch or continuous-flow reactors. ''Acidithiobacillus ferrooxidans'' is commonly found in

and mine

tailings In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that overli ...

. The oxidation of ferrous iron and reduced sulfur oxyanions, metal sulfides and elementary sulfur results in the production of ferric sulfate in sulfuric acid, this in turn causes the solubilization of metals and other compounds. As a result, ''A. ferrooxidans'' may be of interest for

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...

processes. ''Acidithiobacillus'' is also commonly abundant upon inner surfaces of sewers in areas exhibiting corrosion; Genetic Sequencing identifies ''Acidothiobacillus thiooxidans'' as the usual species present, although it is occasionally absent from such locations.Li, X., Kappler, U., Jiang, G., & Bond, P. L. (2017). The Ecology of Acidophilic Microorganisms in the Corroding Concrete Sewer Environment. Frontiers in microbiology, 8, 683. https://doi.org/10.3389/fmicb.2017.00683

Morphology

''Acidithiobacillus'' spp. occur as single cells or occasionally in pairs or chains, depending on growth conditions. Highly motile species have been described, as well as nonmotile ones. Motile strains have a single flagellum with the exception of ''A. albertensis'', which has a tuft of polar flagella and a glycocalyx. Nitrogen fixation also is an important ecological function carried out by some species in this genus, as is growth using molecular hydrogen as a source of energy - neither property is found in every species. Ferric iron can be used by some species as a terminal electron acceptor. *

References

External links