Acidithiobacillus ferrooxidans

Bacteria may catalyze and considerably enhance the oxidation of pyrite and Fe(II) in water, especially under acidic conditions (Welch et al., 2000, 597). Many microbial species actually oxidize only specific elements in sulfides. With pyrite, Acidithiobacillus thiooxidans is important in the oxidation of sulfur, whereas Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans (formerly Thiobacillus fer-rooxidans) oxidize Fe(II) (Gleisner and Herbert, 2002, 140). Acidithiobacillus ferrooxidans obtain energy through Reaction 3.45 (Gleisner and Herbert, 2002, 140). The bacteria are most active at about 30 °C and pH 2-3 (Savage, Bird and Ashley, 2000, 407). Acidithiobacillus sp. and Leptospirillum ferrooxidans have the ability to increase the oxidation of sulfide minerals by about five orders of magnitude (Welch et al., 2000, 597). 

Fe(III) can oxidize arsenopyrite about 10 times faster than pyrite and the rates are even more rapid if Acidithiobacillus ferrooxidans is present (Welch et al., 2000, 597 Gleisner and Herbert, 2002, 140 Evangelou, Seta and Holt, 1998, 2084). Scorodite, a product of Reaction 3.52, may form colloids in water and natural organic matter (NOM) could assist in stabilizing the colloids (Buschmann et al., 2006, 6019). 

Duquesne, K., Lebrun, S., Casiot, C. et al. (2003) Immobilization of arsenite and ferric iron by Acidithiobacillus ferrooxidans and its relevance to acid mine drainage. Applied and Environmental Microbiology, 69(10), 6165— 73. 

Sweet, C.R., Ribeiro, A.A., Raetz, C.R.H. Oxidation and transamination of the 3//-position of UDP-N-acetylglucosamine by enzymes from Acidithiobacillus ferrooxidans Role in the... 

Acidithiobacillus ferrooxidans is able to degrade chalcocite (CU2S) by oxidizing the Cu(I) in the mineral to Cu and the sulphide-S to 804 . Because the end-products of this oxidation are soluble, the oxidation results in the mobilization of the copper and sulphur in the chalcocite. Evidence exists for two distinct mechanisms by which At. ferrooxidans can perform the oxidation of chalcocite. One mechanism involves a direct attack of the crystal lattice of chalcocite by cells attached to the surface of chalcocite. The other mechanism involves an indirect attack of the crystal lattice of chalcocite by the chemical oxidant Fe generated from Fe in the bulk phase by planktonic cells (unattached) oi At. ferrooxidans. 

Yarzabal, A., Brasseur, G., Ratouchniak, J. et al. (2002). The high-molecular-weight cytochrome c Cyc2 of Acidithiobacillus ferrooxidans is an outer membrane protein. Journal of Bacteriology, 184, 313-17. 

Acidithiobacillus thiooxidans, formerly known as Thiobacillus thiooxidans, is an acidophilic bacterium that oxidizes and thiosulfate, but not iron. Due to the rapid kinetics involved in sulfide oxidation by dissolved oxygen, some sulfide-oxidizing bacteria are in continuous competition with the chemical oxidation mechanism. Acidithiobacillus ferrooxidans, formerly known... 

Acidithiobacillus ferrooxidans H2S, sulfide minerals, S(0), S2O3, S4O6, Fe(II)... 

Figure 3. Diagram of a section through the cell wall of Acidithiobacillus ferrooxidans modified from Blake et al. (1992) showing the relationship between iron oxidation and pyrite dissolution. OM =outer membrane, P = periplasm, IM = inner or (cytoplasmic) membrane, cty = cytochrome, pmf = proton motive force. Passage of a proton (driven by proton motive force) into the cell catalyzes the conversion of ADP to ATP. Ferrous iron binds to a component of the electron transport chain, probably a cytochrome c, and is oxidized. The electrons are passed to a terminal reductase where they are combined with O2 and to form water, preventing acidification of the cytoplasm. Ferric iron can either oxidize pyrite (e.g. within the ore body) or form nanocrystalline iron oxyhydroxide minerals (often in surrounding groundwater or streams).

The mechanism hy which these bacteria produce ARD is still debated, but the fact that Acidithiobacillus ferrooxidans is a chemolithoautotropic microorganism that relies on oxidizing ferrous ions (Fe ) to ferric ions (Fe ) is well documented. The bacteria are aerobic, and they catalyze the oxidation by the following reaction ... 

Alvarez, S., and Jerez, C, A, (2004), Copper ions stimulate polyphosphate degradation and phosphate efflux in Acidithiobacillus ferrooxidans. Appl. Environ. Microbiol. 70, 5177-5182,... 

In cultures of sulfur bacteria the reactions at Eqs. (20)-(22) are catalyzed by appropriate enzymes. The sulfane monosulfonate formed in the reaction at Eq. (22) is unstable and decomposes to polythionate anions and elemental sulfur which are the components of Raffo and 8elmi sols as shown above see Eqs. (10) and (11). These reactions take place, for example, if cultures of Acidithiobacillus ferrooxidans (formerly Thiobacillus ferrooxidans) are incubated (mixed) with tetra- or pentathionate at 30 °C in air. After some time all polythionate anions with up to 17 sulfur atoms could be detected by ion-pair chromatography in the filtrated aqueous phase while the sulfur globules excreted extracellularly were isolated and extracted by C82. According to a HPLC analysis this extract contained 8s and small amounts of the homocycles 85, 87, and 812 [53]. 

Steudel proposed a number of models for the composition of bacterial sulfur globules in which he did not always distinguish between intracellular-ly and extracellularly stored sulfur. In a model proposed for sulfur globules excreted by Acidithiobacillus ferrooxidans [39] the globules consist of a sulfur nucleus (mainly Ss rings and small amounts of other sulfur rings) and... 

Acidithiobacillus ferrooxidans 167, 177 Acidoid sol 161, 163 Agriculture 184-185 Allochromatium vinosum 172, 174-176 Allotropes 1, 3-4, 12, 17, 19, 47, 54-57 -, high-pressure 59 Aqueous sulfur sol 154 Assimilatory reduction 169 Aten s sulfur 17... 

Among the acidophilic iron-oxidizing bacteria, Acidithiobacillus ferrooxidans (Kuenen, 1989) and Leptospirillum ferrooxidans (Eccleston et al., 1985) are well... 

In Nature, there reside bacteria that acquire the energy for life processes by oxidizing ferrous ion to ferric ion. Acidithiobacillus ferrooxidans and Leplospirillum ferrooxidans oxidize ferrous ion to ferric ion at pH 2.0 and are the most well known among the bacteria that oxidize ferrous ion. Ferrous ion is easily oxidized spontaneously by molecular oxygen at neutral pH, while at pH 2.0 it is not oxidized spontaneously but is easily oxidized even at pH 2.0 by the action of the acidophilic iron-oxidizing bacteria. These bacteria are utilized in various industrial processes because of their ability to oxidize ferrous to ferric ions at pH 2.0. In particular, A. ferrooxidans has been well studied industrially as well as scientifically. 

Bacterial oxidation of ferrous ion in Acidithiobacillus ferrooxidans occurs by the catalysis of a system consisted of several enzymes and proteins. In the oxidation of ferrous ion by A. ferrooxidans Fel (JCM 7811), electrons are first pulled out of the ion by the catalysis of Fe(II)-cytochrome c oxidoreductase. Then, electrons are transferred to ferricytochrome c-552 (native cytochrome c of the bacterium), fer-rocytochrome c-552 formed is oxidized with oxygen by the catalysis of cytochrome c oxidase (Yamanaka and Fukumori, 1995). However, the mechanism of the oxidation of ferrous ion appears to be a little different between the strains of A. ferrooxidans. Thus, in certain strains of the bacterium the oxidation of ferrous ion is catalyzed by Fe(II)-rusticyanin oxidoreductase (Blake and Shute, 1994). However, as will be pointed out below, the enzyme should be carefully checked. Moreover, in a moderately thermophilic iron-oxidizing bacterium, the oxidation of ferrous ion is reported to be catalyzed by an iron oxidase containing heme A (Takai et al., 1999, 2001). 

Many kinds of cytochromes c occur in Acidithiobacillus ferrooxidans. One of them is water-soluble cytochrome c-552(s) (14 kDa) (hereafter s means soluble, and m means membrane bound) highly purified by Sato et al. (1989). This cytochrome seems to be the same protein as that partially purified by Vernon et al. (1960) and Ingledew (1982). Besides the cytochrome, several c-type cytochromes are obtained cytochrome c-552(m) (22.3 kDa), cytochrome c-550(m) (51 kDa) (Tamegai et al., 1994) Valkova-Valchanova and Chan, 1994) and cytochrome c-552(m) (30 kDa) (Elbehti and Lemesle-Meunier, 1996), cytochrome c4 (21.2 kDa) (Cavazza et al., 1996), and brown soluble cytochrome c-553 (12789 Da) (Cavazza and Bruschi, 1995). Furthermore, occurrence of several cytochromes c besides those mentioned above has been indicated (Yarzabal et al., 2002a). It has also been reported that cytochrome c (46 kDa) occurs in the outer membrane of the bacterium and participates in removing electrons from insoluble iron compounds such as pyrite (Yarzabal et al., 2002b). 

Cytochrome c-552(s) (14kDa) of Acidithiobacillus ferrooxidans acts not only as the electron acceptor for Fe(II)-cytochrome c oxidoreductase but also as the electron donor for cytochrome c oxidase. Cytochromes c-552(m) (22.3 kDa) and c-550(m) (51 kDa) also act as the electron donor for cytochrome c oxidase although it has not yet been clarified whether they act as the electron acceptors for Fe(II)-cytochrome c oxidoreductase. The reactivity with cytochrome c oxidase of cytochrome c-550(m) is larger than that of cytochrome c-552(s), while the reactivity of cytochrome c-552(m) is much less than that of cytochrome c-552(s) (Kai et al., 1992 Yamanaka and Fukumori, 1995). However, a big difference is observed in the effect of sulfate on the reactions with the oxidase between these cytochromes c the reaction with the oxidase of cytochrome c-552(s) is much stimulated by sulfate ion, while those of cytochromes c-552(m) and c-550(m) are inhibited by the ion. Considering that Acidithiobacillus ferrooxidans requires sulfate for its growth (Lazaroff, 1963), the stimulation of the reaction with the oxidase of cytochrome c by sulfate ion seems to suggest that cytochrome c-552(s) is a real electron donor for cytochrome c oxidase, although several kinds of cytochromes c occur in the bacterium (cf. Fig. 5.2). 

Cytochrome c oxidase of Acidithiobacillus ferrooxidans was previously called cytochrome a1( as it shows the a peak at 595 nm (Ingledew, 1982). However, as the oxidase purified from the bacterium has two heme A molecules and two copper atoms in the minimal functional unit and one of the two molecules of heme A combines with carbon monoxide, it is a cytochrome aa3-type cytochrome c oxidase although it has the a peak at 595 nm (Kai et al., 1992). It differs from the usual cytochrome aa3 in having only one molecule of heme A and one atom of copper in the minimal structural unit, which comprises one molecule each of three kinds of subunits (54 kDa, 21 kDa, 15 kDa) like Starkeya novella cytochrome c oxidase (Shoji et al., 1992). [The DNA study suggests the presence of four subunits with the molecular masses of 69, 28, 18 and 6.4 kDa (Appia-Ayme et al., 1999)]. The minimal functional unit of the A. ferrooxidans oxidase is a dimer of the minimal structural unit, and the dimer shows general properties of cytochrome ach except that the a peak is present at a wavelength shorter than 600 nm of the absorption spectrum. The oxidase resembles Nitrosomonas europaea cytochrome c oxidase (Yamazaki et al., 1985) (see pp. 25-26) in the position of the a peak of the absorption spectrum. 

Fig. 5.1. Electron transfer pathway in the oxidation of ferrous ion by Acidithiobacillus ferrooxidans Fel (JCM 7811) (prepared on the basis of Fukumori et al., 1988b Sato et al., 1989 Kai et al., 1992 Tamegai et al., 1994). Dashed line with arrow, unverified Cyt, cytochrome...

Acidithiobacillus ferrooxidans grows on formate at concentrations below 100 pM but its growth is inhibited by the compound at higher concentrations than 100 pM... 

Acidithiobacillus ferrooxidans anaerobically oxidizes elemental sulfur and formate with ferric ion (Sugio et al., 1985 Pronk et al., 1991a Das et al., 1992). The bacterial oxidation of elemental sulfur and formate with ferric ion is inhibited by HOQNO but not by azide. In the oxidation of elemental sulfur with ferric ion free energy of 75 kcal/S° is liberated, which is enough to support the growth of the bacterium. Thus, the bacterium grows anaerobically by oxidizing elemental sulfur with ferric ion (Pronk et al., 1992). 

Fig. 5.3. A diagram of the apparatus for the bacterial leaching on a laboratory scale. The acidophilic iron-oxidizing bacteria (e.g., Acidithiobacillus ferrooxidans) are present in the pool and oxidize ferrous ion to ferric ion...

Botuyan MV, Toy-Palmer A, Chung J, Blake RC Jr, Beroza P, Case DA, Dyson HJ (1996) NMR solution structure of Cu(I) rusticyanin from Thiobacillus ferrooxidans structural basis for the extreme acid stability and redox potential. J Mol Biol 263 752-767 Bramblett RN, Peck HD Jr (1975) Some physical and kinetic properties of adenylyl sulfate reductase from Desulfovibrio vulgaris. J Biol Chem 250 2979-2986 Brasseur G, Bruscella P, Bonnefoy V, Lamesle-Meunier D (2002) The be, complex of the iron-grown acidophilic chemolithotrophic bacterium Acidithiobacillus ferrooxidans in the reverse but not in the forward direction. Is there a second be, complex Biochim Biophys Acta 1555 37 13... 

Bruscella P, Cassagnaud L, Ratouchniak J, Brasseur G, Lojou E, Amils R, Bonnefoy V (2005) The HiPIP from the acidophilic Acidithiobacillus ferrooxidans is correctly processed and translocated in Escherichia coli, in spite of the periplasm pH difference between these two micro-organisms. Microbiology 151 1421-1431... 

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