Differential expression of two bc 1 complexes in the strict acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans suggests a model for their respective roles in iron or sulfur oxidation. Microbiology 153: 102-110

University of Santiago, Chile, CiudadSantiago, Santiago Metropolitan, Chile
Microbiology (Impact Factor: 2.56). 02/2007; 153(Pt 1):102-10. DOI: 10.1099/mic.0.2006/000067-0
Source: PubMed


Three strains of the strict acidophilic chemolithoautotrophic Acidithiobacillus ferrooxidans, including the type strain ATCC 23270, contain a petIIABC gene cluster that encodes the three proteins, cytochrome c1, cytochrome b and a Rieske protein, that constitute a bc1 electron-transfer complex. RT-PCR and Northern blotting show that the petIIABC cluster is co-transcribed with cycA, encoding a cytochrome c belonging to the c4 family, sdrA, encoding a putative short-chain dehydrogenase, and hip, encoding a high potential iron-sulfur protein, suggesting that the six genes constitute an operon, termed the petII operon. Previous results indicated that A. ferrooxidans contains a second pet operon, termed the petI operon, which contains a gene cluster that is similarly organized except that it lacks hip. Real-time PCR and Northern blot experiments demonstrate that petI is transcribed mainly in cells grown in medium containing iron, whereas petII is transcribed in cells grown in media containing sulfur or iron. Primer extension experiments revealed possible transcription initiation sites for the petI and petII operons. A model is presented in which petI is proposed to encode the bc1 complex, functioning in the uphill flow of electrons from iron to NAD(P), whereas petII is suggested to be involved in electron transfer from sulfur (or formate) to oxygen (or ferric iron). A. ferrooxidans is the only organism, to date, to exhibit two functional bc1 complexes.

Download full-text


Available from: David S Holmes,
  • Source
    • "These operons are differentially transcribed in response to growth conditions. Namely, bc 1 complex form II encoded by the pet II operon is preferably expressed in S 0 -cells (Bruscella et al. 2007). Part of the pet II operon is a short-chain dehydrogenase/ reductase family protein (SdrA2; spot No. 318, AFE_0377). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Elemental sulfur oxidation by ferric iron in Acidithiobacillus ferrooxidans was investigated. The apparent Michaelis constant for ferric iron was 18.6 mM. An absence of anaerobic ferric iron reduction ability was observed in bacteria maintained on elemental sulfur for an extended period of time. Upon transition from ferrous iron to elemental sulfur medium, the cells exhibited similar kinetic characteristics of ferric iron reduction under anaerobic conditions to those of cells that were originally maintained on ferrous iron. Nevertheless, a total loss of anaerobic ferric iron reduction ability after the sixth passage in elemental sulfur medium was demonstrated. The first proteomic screening of total cell lysates of anaerobically incubated bacteria resulted in the detection of 1599 protein spots in the master two-dimensional electrophoresis gel. A set of 59 more abundant and 49 less abundant protein spots that changed their protein abundances in an anaerobiosis-dependent manner was identified and compared to iron- and sulfur-grown cells, respectively. Proteomic analysis detected a significant increase in abundance under anoxic conditions of electron transporters, such as rusticyanin and cytochrome c(552), involved in the ferrous iron oxidation pathway. Therefore we suggest the incorporation of rus-operon encoded proteins in the anaerobic respiration pathway. Two sulfur metabolism proteins were identified, pyridine nucleotide-disulfide oxidoreductase and sulfide-quinone reductase. The important transcription regulator, ferric uptake regulation protein, was anaerobically more abundant. The anaerobic expression of several proteins involved in cell envelope formation indicated a gradual adaptation to elemental sulfur oxidation.
    Antonie van Leeuwenhoek 11/2011; 101(3):561-73. DOI:10.1007/s10482-011-9670-2 · 1.81 Impact Factor
  • Source
    • "It was suggested about a decade ago that the cellular ATP/ADP ratio regulates the balance of reducing equivalents from Fe(II), favouring either the activation of the aa3 cytochrome oxidase and thus promote the downhill pathway or, conversely, the repression of the aa3 cytochrome oxidase promoting the use of the uphill pathway (Elbehti et al., 2000). In addition to regulatory decisions regarding the flux of electrons uphill or downhill, At. ferrooxidans also regulates enzymes and electron carriers depending on whether its energetic substrate is Fe(II) or RISCs (Yarzabal et al., 2004; Bruscella et al., 2007; Amouric et al., 2009; Quatrini et al., 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: This minireview presents recent advances in our understanding of iron oxidation and homeostasis in acidophilic Bacteria and Archaea. These processes influence the flux of metals and nutrients in pristine and man-made acidic environments such as acid mine drainage and industrial bioleaching operations. Acidophiles are also being studied to understand life in extreme conditions and their role in the generation of biomarkers used in the search for evidence of existing or past extra-terrestrial life. Iron oxidation in acidophiles is best understood in the model organism Acidithiobacillus ferrooxidans. However, recent functional genomic analysis of acidophiles is leading to a deeper appreciation of the diversity of acidophilic iron-oxidizing pathways. Although it is too early to paint a detailed picture of the role played by lateral gene transfer in the evolution of iron oxidation, emerging evidence tends to support the view that iron oxidation arose independently more than once in evolution. Acidic environments are generally rich in soluble iron and extreme acidophiles (e.g. the Leptospirillum genus) have considerably fewer iron uptake systems compared with neutrophiles. However, some acidophiles have been shown to grow as high as pH 6 and, in the case of the Acidithiobacillus genus, to have multiple iron uptake systems. This could be an adaption allowing them to respond to different iron concentrations via the use of a multiplicity of different siderophores. Both Leptospirillum spp. and Acidithiobacillus spp. are predicted to synthesize the acid stable citrate siderophore for Fe(III) uptake. In addition, both groups have predicted receptors for siderophores produced by other microorganisms, suggesting that competition for iron occurs influencing the ecophysiology of acidic environments. Little is known about the genetic regulation of iron oxidation and iron uptake in acidophiles, especially how the use of iron as an energy source is balanced with its need to take up iron for metabolism. It is anticipated that integrated and complex regulatory networks sensing different environmental signals, such as the energy source and/or the redox state of the cell as well as the oxygen availability, are involved.
    Environmental Microbiology 11/2011; 14(7):1597-611. DOI:10.1111/j.1462-2920.2011.02626.x · 6.20 Impact Factor
  • Source
    • "This second bc1 complex has been proposed to function directly transferring electrons from sulfur to oxygen (Figure 2), and possibly in the aerobic and anaerobic oxidation of sulfur and formate described by Pronk et al. [55]. In that case, the bc1 complex receives the electrons from the quinol pool and transfers them to the membrane-bound cytochrome c4 CycA2 and/or to the periplasmic high potential iron-sulfur protein Hip that subsequently gives the electrons to the terminal oxidase [2,13,14] (Figure 2). SdrA2, like SdrA1 (see above), may promote electron flow from the quinone pool to the NADH complex (Figure 2). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Acidithiobacillus ferrooxidans gains energy from the oxidation of ferrous iron and various reduced inorganic sulfur compounds at very acidic pH. Although an initial model for the electron pathways involved in iron oxidation has been developed, much less is known about the sulfur oxidation in this microorganism. In addition, what has been reported for both iron and sulfur oxidation has been derived from different A. ferrooxidans strains, some of which have not been phylogenetically characterized and some have been shown to be mixed cultures. It is necessary to provide models of iron and sulfur oxidation pathways within one strain of A. ferrooxidans in order to comprehend the full metabolic potential of the pangenome of the genus. Bioinformatic-based metabolic reconstruction supported by microarray transcript profiling and quantitative RT-PCR analysis predicts the involvement of a number of novel genes involved in iron and sulfur oxidation in A. ferrooxidans ATCC23270. These include for iron oxidation: cup (copper oxidase-like), ctaABT (heme biogenesis and insertion), nuoI and nuoK (NADH complex subunits), sdrA1 (a NADH complex accessory protein) and atpB and atpE (ATP synthetase F0 subunits). The following new genes are predicted to be involved in reduced inorganic sulfur compounds oxidation: a gene cluster (rhd, tusA, dsrE, hdrC, hdrB, hdrA, orf2, hdrC, hdrB) encoding three sulfurtransferases and a heterodisulfide reductase complex, sat potentially encoding an ATP sulfurylase and sdrA2 (an accessory NADH complex subunit). Two different regulatory components are predicted to be involved in the regulation of alternate electron transfer pathways: 1) a gene cluster (ctaRUS) that contains a predicted iron responsive regulator of the Rrf2 family that is hypothesized to regulate cytochrome aa3 oxidase biogenesis and 2) a two component sensor-regulator of the RegB-RegA family that may respond to the redox state of the quinone pool. Bioinformatic analysis coupled with gene transcript profiling extends our understanding of the iron and reduced inorganic sulfur compounds oxidation pathways in A. ferrooxidans and suggests mechanisms for their regulation. The models provide unified and coherent descriptions of these processes within the type strain, eliminating previous ambiguity caused by models built from analyses of multiple and divergent strains of this microorganism.
    BMC Genomics 09/2009; 10(1):394. DOI:10.1186/1471-2164-10-394 · 3.99 Impact Factor
Show more