Acidithiobacillus caldus

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Acidithiobacillus caldus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Bacteria
Phylum: Pseudomonadota
Class: Acidithiobacillia
Order: Acidithiobacillales
Family: Acidithiobacillaceae
Genus: Acidithiobacillus
Species:
A. caldus
Binomial name
Acidithiobacillus caldus
(Kelly and Wood 2000)
Type strain
DSM 8584
(Kelly & Wood 2000)
Synonyms

Thiobacillus caldus
(Hallberg & Lindstrom 1994)

Acidithiobacillus caldus formerly belonged to the genus Thiobacillus prior to 2000, when it was reclassified along with a number of other bacterial species into one of three new genera that better categorize sulfur-oxidizing acidophiles. [1] As a member of the Gammaproteobacteria class of Pseudomonadota, A. caldus may be identified as a Gram-negative bacterium that is frequently found in pairs. [2] Considered to be one of the most common microbes involved in biomining, it is capable of oxidizing reduced inorganic sulfur compounds (RISCs) that form during the breakdown of sulfide minerals. [3] The meaning of the prefix acidi- in the name Acidithiobacillus comes from the Latin word acidus, signifying that members of this genus love a sour, acidic environment. Thio is derived from the Greek word thios and describes the use of sulfur as an energy source, and bacillus describes the shape of these microorganisms, which are small rods. [1] The species name, caldus, is derived from the Latin word for warm or hot, denoting this species' love of a warm environment.

Contents

History

Thiobacillus caldus was reclassified into Acidithiobacillus, one of three new genera (also including Halothiobacillus and Thermithiobacillus) created to further classify members of the genus which fall into the alpha-, beta-, and gamma-classes of the Pseudomonadota. Thiobacillus species exhibit a tremendous amount of diversity in physiology and DNA composition, which was one reason for reclassification of this species into a new genus containing four species of acidophiles (microorganisms which function best in an acidic environment), some of which are also capable of oxidizing iron[II] and sulfide minerals. [1]

A. caldus, originally isolated from spoils of unneeded rocks encountered when mining coal, was the first acidophilic species of thermophilic thiobacilli to be described. [2] The type strain of this species, DSM 8584, also known as strain KU, has been deposited in the Deutsche Sammlung von Mikroorganismen und Zellkulturen, a collection of microorganisms in Germany. [1]

Morphology

A. caldus is a short, rod-shaped, Gram-negative bacterium that possesses motility via a single polar flagellum located on its outer cell wall, which displays characteristics of a typical Gram-negative cell wall. It is about 1 by 1-2 μm in length and frequently is found in pairs. Different strains have been shown to vary in size when compared to one another. One of the smaller strains, BC13, has a diameter around 0.7 μm and is about 1.2 μm in length, whereas strain KU is a little longer, with a diameter of roughly 0.8 μm and a length around 1.8 μm. [2]

Physiological tolerance

A. caldus displays tolerance to a broad range of conditions, including acidic pH levels and temperature, with the best growth occurring at a pH of 2.0 to 2.5 and a temperature of 45 °C. Optimal growth results in a short generation time of 2–3 hours, depending on the environmental factors present. [2] A. caldus is not considered to be halophilic because it displayed no signs of growth in environments containing NaCl. [4]

Temperature

A. caldus is moderately thermophilic and thrives at an optimum temperature of 45 °C. [2] Certain strains, such as strain KU, have still been shown to exhibit growth on a tetrathionate medium in conditions with a temperature range as low as 32 °C and as high as 52 °C. [4] When grown on a medium containing sulfur, strain BC13 has been found to tolerate temperatures as high as 55 °C. [2] A genetic basis is thought to exist for the extreme temperature tolerance shown by A. caldus as compared to other species in its genus, such as A. ferrooxidans and A. thiooxidans. [5]

pH

As with all acidophilic microorganisms, A. caldus thrives best in an environment with a low, acidic pH with a preferred pH range of 2.0-2.5. [2] This microorganism is capable of coping with a large pH gradient across the cellular membrane, keeping its intracellular pH around a nearly neutral level of 6.5. [6] Certain strains, including KU and BC13, have been found to display signs of growth in a broad, acidic pH range, with a slow growth rate involving a longer generation time, about 45 hours, at a pH of 4.0 and a rate of 6–7 hours at a pH of 1.0. A. caldus has its shortest generation time of 2–3 hours in conditions involving a pH between 2.0 and 2.5. No growth was observed at a pH of 0.5, [2] showing that some conditions are simply too acidic to support the growth of even extreme acidophiles.

Metabolism

A. caldus is capable of oxidizing reduced inorganic sulfur compounds along with other substrates including molecular hydrogen, and formate, in addition to numerous organic compounds and sulfide minerals. It displays chemolithotrophic growth when exposed to substrates containing sulfur, tetrathionate, or thiosulfate, with sulfate being produced as the end product. [2] Reduced sulfur compounds are used by A. caldus to support its autotrophic growth in an environment which lacks sunlight. [1] The growth of A. caldus is enhanced when the air used for sparging, a process by which bubbles of a chemically inert gas are pumped through a liquid, is supplemented with 2% (w/v) CO2. [2] Neither 0.05% yeast extract (a yeast product formed when a cell's walls are removed and its internal contents are extracted [7] ), casamino acids (an amino acid/peptide mixture common to microbial growth media formed from the acid hydrolysis of casein [8] ), nor a 2.5 mM concentration of glucose as the sole substrate have been shown to induce heterotrophic growth of A. caldus. Instead, growth is seen to occur mixotrophically with tetrathionate and yeast extract or glucose. Strain BC13 is capable of growth on a glucose medium, but not after being transferred to a glucose medium from one that contained sulfur in addition to glucose. [2]

Key intermediates in the metabolism of A. caldus are elemental sulfur (S0) and tetrathionate. The hydrolysis of tetrathionate by the key enzyme tetrathionate hydrolase (tetH), composed of 503 amino acids, yields pentathionate, thiosulfate, and sulfur, while elemental sulfur is oxidized by sulfite into sulfate. [3]

Genomics

Most of what is known about the genus Acidithiobacillus comes from experimentation and genomic analyses of two of its species: A. ferrooxidans and A. caldus. With a length of 2,932,225 base pairs, the genomic sequence of A. caldus is GC-rich with a GC content (mol%) in the range of 63.1-63.9% for strain KU [4] and 61.7% for strain BC13. [2] DNA hybridization studies have revealed that strains KU and BC13 exhibited 100% homology with each other, yet showed no DNA hybridization of significance (2-20%) with other species in the genus including A. ferrooxidans and A. thiooxidans, or with other similar Pseudomonadota, such as Thiomonas cuprina or Thiobacillus thioparus. [1]

Strains of A. caldus have been differentiated from other related acidithiobacilli, including A. ferrooxidans and A. thiooxidans, by sequence analyses of the PCR-amplified 16S-23S rDNA intergenic spacer (ITS) and restriction fragment length polymorphism. [9] Phylogenetic analysis of ITS sequences was sufficient to differentiate three unique species of Acidithiobacillus that were found to have slightly different physiological tolerances. The 16S-23S rDNA spacer region is a useful target for developing molecular methods that focus on the detection, rapid differentiation, and identification of Acidithiobacillus species. [9]

Applications

Since its discovery in 1994, A. caldus has been found to have a significant practical application in the industrial field of biomining and mineral biotechnology, contributing to the enhanced recovery of desired minerals from rocks known as ores. [3] Metals such as gold have been recovered from ores which contain pyrite (also known as fool's gold) and arsenopyrite, two sulfide minerals that are often associated with considerable amounts of this precious metal. [2]

Biomining refers to both biooxidation, where the sulfide mineral surrounding the desired metal is oxidized to expose the metal of interest, and bioleaching, where the sulfide mineral is solubilized to obtain the metal of interest. [3] Due to the exothermic nature of bioleaching, the thermophilic nature of A. caldus allows for less cooling and quicker rates of bioleaching overall. [2] Bacteria belonging to the genus Acidithiobacillus possess the ability to oxidize sulfidic ores and thereby solubilize metals. This ability has contributed to a general public interest in this microorganism because of its application in the industrial bioleaching of metals from ores and because of its effective means by which to recover precious metals. [2] Bacteria involved in bioleaching function primarily to produce Fe3+ from the oxidation of ferrous iron, which is then used to carry out sulfur oxidization, which provides an essential energy source for important cellular metabolic functions [3]

Related Research Articles

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.

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 University in the United States of America. While over 30 "species" have been named in this genus since it was defined by Martinus Beijerinck in 1904,, most names were never validly or effectively published. The remainder were either reclassified into Paracoccus, Starkeya ; Sulfuriferula, Annwoodia, Thiomonas ; Halothiobacillus, Guyparkeria, or Thermithiobacillus or Acidithiobacillus. The very loosely defined "species" Thiobacillus trautweinii was where sulfur oxidising heterotrophs and chemolithoheterotrophs were assigned in the 1910-1960s era, most of which were probably Pseudomonas species. Many species named in this genus were never deposited in service collections and have been lost.

<i>Acidithiobacillus</i> Genus of bacteria

Acidithiobacillus is a genus of the Acidithiobacillia in the phylum "Pseudomonadota". This genus includes ten species of acidophilic microorganisms capable of sulfur and/or iron oxidation: Acidithiobacillus albertensis, Acidithiobacillus caldus, Acidithiobacillus cuprithermicus, Acidithiobacillus ferrianus, Acidithiobacillus ferridurans, Acidithiobacillus ferriphilus, Acidithiobacillus ferrivorans, Acidithiobacillus ferrooxidans, Acidithiobacillus sulfuriphilus, and Acidithiobacillus thiooxidans.A. ferooxidans is the most widely studied of the genus, but A. caldus and A. thiooxidans are also significant in research. Like all "Pseudomonadota", Acidithiobacillus spp. are Gram-negative and non-spore forming. They also play a significant role in the generation of acid mine drainage; a major global environmental challenge within the mining industry. Some species of Acidithiobacillus are utilized in bioleaching and biomining. A portion of the genes that support the survival of these bacteria in acidic environments are presumed to have been obtained by horizontal gene transfer.

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 of 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 H
2 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.

Microbial corrosion, also called microbiologically influenced corrosion (MIC), microbially induced corrosion (MIC) or biocorrosion, is "corrosion affected by the presence or activity (or both) of microorganisms in biofilms on the surface of the corroding material." This corroding material can be either a metal (such as steel or aluminum alloys) or a nonmetal (such as concrete or glass).

<i>Ferroplasma</i> Genus of archaea

Ferroplasma is a genus of Archaea that belong to the family Ferroplasmaceae. Members of the Ferroplasma are typically acidophillic, pleomorphic, irregularly shaped cocci.

Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions. These organisms can be found in different branches of the tree of life, including Archaea, Bacteria, and Eukarya.

<span class="mw-page-title-main">Biomining</span> Technique of extracting metals from ores using prokaryotes or fungi

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. Large chemostats of microbes can be grown to leach 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. Bacteria can mine for metals, clean oil spills, purify gold, and use radioactive elements for energy.

<span class="mw-page-title-main">Thiosulfate dehydrogenase</span>

Thiosulfate dehydrogenase is an enzyme that catalyzes the chemical reaction:

Thermithiobacillus tepidarius is a member of the Acidithiobacillia isolated from the thermal groundwaters of the Roman Baths at Bath, Somerset, United Kingdom. It was previously placed in the genus Thiobacillus. The organism is a moderate thermophile, 43–45 °C (109–113 °F), and an obligate aerobic chemolithotrophic autotroph. Despite having an optimum pH of 6.0–7.5, growth can continue to an acid medium of pH 4.8. Growth can only occur on reduced inorganic sulfur compounds and elementary sulfur, but unlike some species in other genus of the same family, Acidithiobacillus, Thermithiobacillus spp. are unable to oxidise ferrous iron or iron-containing minerals.

Sulfur is metabolized by all organisms, from bacteria and archaea to plants and animals. Sulfur can have an oxidation state from -2 to +6 and is reduced or oxidized by a diverse range of organisms. The element is present in proteins, sulfate esters of polysaccharides, steroids, phenols, and sulfur-containing coenzymes.

<span class="mw-page-title-main">Acidophiles in acid mine drainage</span>

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.

Iron:rusticyanin reductase is an enzyme with systematic name Fe(II):rusticyanin oxidoreductase. This enzyme catalyses the following chemical reaction

<i>Acidimicrobium ferrooxidans</i> Species of bacterium

Acidimicrobium ferrooxidans is a bacterium, the type species of its genus. It is a ferrous-iron-oxidizing, moderately thermophilic and acidophilic bacterium.

Sulfolobus metallicus is a coccoid shaped thermophilic archaeon. It is a strict chemolithoautotroph gaining energy by oxidation of sulphur and sulphidic ores into sulfuric acid. Its type strain is Kra 23. It has many uses that take advantage of its ability to grow on metal media under acidic and hot environments.

<i>Acidithiobacillus thiooxidans</i> Species of bacterium

Acidithiobacillus thiooxidans, formerly known as Thiobacillus thiooxidans until its reclassification into the newly designated genus Acidithiobacillus of the Acidithiobacillia subclass of Pseudomonadota, is a Gram-negative, rod-shaped bacterium that uses sulfur as its primary energy source. It is mesophilic, with a temperature optimum of 28 °C. This bacterium is commonly found in soil, sewer pipes, and cave biofilms called snottites. A. thiooxidans is used in the mining technique known as bioleaching, where metals are extracted from their ores through the action of microbes.

Metallosphaera sedula is a species of Metallosphaera that is originally isolated from a volcanic field in Italy. Metallosphaera sedula can be roughly translated into “metal mobilizing sphere” with the word “sedulus” meaning busy, describing its efficiency in mobilizing metals. M. sedula is a highly thermoacidophilic Archaean that is unusually tolerant of heavy metals.

<span class="mw-page-title-main">Microbial oxidation of sulfur</span>

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 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).

Sulfobacillus thermosulfidooxidans is a species of bacteria of the genus Sulfobacillus. It is an acidophilic, mixotrophic, moderately thermophilic, Gram-positive, sporulating facultative anaerobe. As its name suggests, it is capable of oxidizing sulfur.

References

  1. 1 2 3 4 5 6 Kelly, Donovan P.; Wood, Ann P. (2000). "Reclassification of some species of Thiobacillus to the newly designated genera Acidithiobacillus gen. nov., Halothiobacillus gen. nov. and Thermithiobacillus gen. nov". International Journal of Systematic and Evolutionary Microbiology. 50 (2): 511–516. doi: 10.1099/00207713-50-2-511 . PMID   10758854.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Hallberg, Kevin B.; Lindström, E. Börje (1994). "Characterization of Thiobacillus caldus sp. nov., a moderately thermophilic acidophile". Microbiology. 140 (12): 3451–3456. doi: 10.1099/13500872-140-12-3451 . PMID   7533596.
  3. 1 2 3 4 5 Rzhepishevska, Olena I.; et al. (2007). "Regulation of a novel Acidithiobacillus caldus gene cluster involved in metabolism of reduced inorganic sulfur compounds". Applied and Environmental Microbiology. 73 (22): 7367–7372. Bibcode:2007ApEnM..73.7367R. doi:10.1128/aem.01497-07. PMC   2168230 . PMID   17873067.
  4. 1 2 3 You, Xiao-Yan; et al. (2011). "Unraveling the Acidithiobacillus caldus complete genome and its central metabolisms for carbon assimilation". Journal of Genetics and Genomics. 38 (6): 243–252. doi:10.1016/j.jgg.2011.04.006. PMID   21703548.
  5. ↑ Valdes, Jorge; Pedroso, Inti; Quatrini, Raquel; Holmes, David S. (2008). "Comparative genome analysis of Acidithiobacillus ferrooxidans, A. thiooxidans and A. caldus: insights into their metabolism and ecophysiology". Hydrometallurgy. 94 (1–4): 180–184. Bibcode:2008HydMe..94..180V. doi:10.1016/j.hydromet.2008.05.039. hdl: 10533/142069 .
  6. ↑ Mangold, Stephanie; et al. (2013). "Response of Acidithiobacillus caldus toward suboptimal pH conditions". Extremophiles. 17 (4): 689–696. doi:10.1007/s00792-013-0553-5. PMID   23712908. S2CID   14275938.
  7. ↑ Herbst, Sharon (2001). Food Lover's Companion. Hauppauge, New York: Barron's Educational Series, Inc.
  8. ↑ Mueller, J. Howard; Johnson, Everett R. (1941). "Acid hydrolysates of casein to replace peptone in the preparation of bacteriological media". The Journal of Immunology. 40 (1): 33–38. doi: 10.4049/jimmunol.40.1.33 . S2CID   88040100.
  9. 1 2 Bergamo, Rogério F.; Novo, Maria Teresa M.; Verissimo, Ricardo V.; Paulino, Luciana C.; Stoppe, Nancy C.; Sato, Maria Inês Z.; Manfio, Gilson P.; Inácio Prado, Paulo; Garcia Jr., Garcia; Ottoboni, Laura M.M. (2004). "Differentiation of Acidithiobacillus ferrooxidans and A. thiooxidans strains based on 16S-23S rDNA spacer polymorphism analysis". Research in Microbiology. 155 (7): 559–567. doi:10.1016/j.resmic.2004.03.009. PMID   15313256.

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