c-Type Cytochromes in Pelobacter carbinolicus

Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA.
Applied and Environmental Microbiology (Impact Factor: 3.67). 12/2006; 72(11):6980-5. DOI: 10.1128/AEM.01128-06
Source: PubMed


Previous studies failed to detect c-type cytochromes in Pelobacter species despite the fact that other close relatives in the Geobacteraceae, such as Geobacter and Desulfuromonas species, have abundant c-type cytochromes. Analysis of the recently completed genome sequence of Pelobacter carbinolicus revealed 14 open reading frames that could encode c-type cytochromes. Transcripts for all but one of these open reading frames were detected in acetoin-fermenting and/or Fe(III)-reducing
cells. Three putative c-type cytochrome genes were expressed specifically during Fe(III) reduction, suggesting that the encoded proteins may participate
in electron transfer to Fe(III). One of these proteins was a periplasmic triheme cytochrome with a high level of similarity
to PpcA, which has a role in Fe(III) reduction in Geobacter sulfurreducens. Genes for heme biosynthesis and system II cytochrome c biogenesis were identified in the genome and shown to be expressed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis
gels of protein extracted from acetoin-fermenting P. carbinolicus cells contained three heme-staining bands which were confirmed by mass spectrometry to be among the 14 predicted c-type cytochromes. The number of cytochrome genes, the predicted amount of heme c per protein, and the ratio of heme-stained protein to total protein were much smaller in P. carbinolicus than in G. sulfurreducens. Furthermore, many of the c-type cytochromes that genetic studies have indicated are required for optimal Fe(III) reduction in G. sulfurreducens were not present in the P. carbinolicus genome. These results suggest that further evaluation of the functions of c-type cytochromes in the Geobacteraceae is warranted.

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Available from: Dawn E Holmes, Dec 22, 2015
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    • "P. carbinolicus belongs to the family Desulfuromonadaceae[4-7] and Pelobacter propionicus to Geobacteraceae. The complete genome sequence of P. carbinolicus has led to the discoveries that it expresses c-type cytochromes [8] and that it utilizes Fe(III) as a terminal electron acceptor indirectly via reduction of S° [9]. In silico metabolic models have been constructed for P. carbinolicus and P. propionicus[10], their genomes have been compared to those of acetate-oxidizing, non-fermentative Geobacteraceae[11], and a shortage of histidyl-tRNA caused by the CRISPR locus has been proposed to account for the loss of some ancestral genes such as multiheme c-type cytochromes by the P. carbinolicus genome [12]. "
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    ABSTRACT: Background The bacterium Pelobacter carbinolicus is able to grow by fermentation, syntrophic hydrogen/formate transfer, or electron transfer to sulfur from short-chain alcohols, hydrogen or formate; it does not oxidize acetate and is not known to ferment any sugars or grow autotrophically. The genome of P. carbinolicus was sequenced in order to understand its metabolic capabilities and physiological features in comparison with its relatives, acetate-oxidizing Geobacter species. Results Pathways were predicted for catabolism of known substrates: 2,3-butanediol, acetoin, glycerol, 1,2-ethanediol, ethanolamine, choline and ethanol. Multiple isozymes of 2,3-butanediol dehydrogenase, ATP synthase and [FeFe]-hydrogenase were differentiated and assigned roles according to their structural properties and genomic contexts. The absence of asparagine synthetase and the presence of a mutant tRNA for asparagine encoded among RNA-active enzymes suggest that P. carbinolicus may make asparaginyl-tRNA in a novel way. Catabolic glutamate dehydrogenases were discovered, implying that the tricarboxylic acid (TCA) cycle can function catabolically. A phosphotransferase system for uptake of sugars was discovered, along with enzymes that function in 2,3-butanediol production. Pyruvate:ferredoxin/flavodoxin oxidoreductase was identified as a potential bottleneck in both the supply of oxaloacetate for oxidation of acetate by the TCA cycle and the connection of glycolysis to production of ethanol. The P. carbinolicus genome was found to encode autotransporters and various appendages, including three proteins with similarity to the geopilin of electroconductive nanowires. Conclusions Several surprising metabolic capabilities and physiological features were predicted from the genome of P. carbinolicus, suggesting that it is more versatile than anticipated.
    Full-text · Article · Dec 2012 · BMC Genomics
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    • "Unlike Geobacter and Desulfuromonas species, P. carbinolicus lacks most of the c-type cytochromes [12], which are essential for optimal electron transfer to Fe(III) in Geobacter sulfurreducens [13-16]. P. carbinolicus reduces Fe(III) via an indirect mechanism in which elemental sulfur is reduced to sulfide and the sulfide reduces Fe(III) with the regeneration of elemental sulfur, contrasting with the direct reduction of Fe(III) for Geobacter species [17]. "
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    ABSTRACT: Pelobacter species are commonly found in a number of subsurface environments, and are unique members of the Geobacteraceae family. They are phylogenetically intertwined with both Geobacter and Desulfuromonas species. Pelobacter species likely play important roles in the fermentative degradation of unusual organic matters and syntrophic metabolism in the natural environments, and are of interest for applications in bioremediation and microbial fuel cells. In order to better understand the physiology of Pelobacter species, genome-scale metabolic models for Pelobacter carbinolicus and Pelobacter propionicus were developed. Model development was greatly aided by the availability of models of the closely related Geobacter sulfurreducens and G. metallireducens. The reconstructed P. carbinolicus model contains 741 genes and 708 reactions, whereas the reconstructed P. propionicus model contains 661 genes and 650 reactions. A total of 470 reactions are shared among the two Pelobacter models and the two Geobacter models. The different reactions between the Pelobacter and Geobacter models reflect some unique metabolic capabilities such as fermentative growth for both Pelobacter species. The reconstructed Pelobacter models were validated by simulating published growth conditions including fermentations, hydrogen production in syntrophic co-culture conditions, hydrogen utilization, and Fe(III) reduction. Simulation results matched well with experimental data and indicated the accuracy of the models. We have developed genome-scale metabolic models of P. carbinolicus and P. propionicus. These models of Pelobacter metabolism can now be incorporated into the growing repertoire of genome scale models of the Geobacteraceae family to aid in describing the growth and activity of these organisms in anoxic environments and in the study of their roles and interactions in the subsurface microbial community.
    Preview · Article · Dec 2010 · BMC Systems Biology
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    • "The individual heme bands were visualized by separation of proteins on 15% SDS- PAGE by the method of Francis and Becker (1984). The stained bands were excised from the gel and digested with trypsin (Haveman et al., 2006). "
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    ABSTRACT: Characterizing proteins recovered from natural microbial communities affords the opportunity to correlate protein expression and modification with environmental factors, including species composition and successional stage. Proteogenomic and biochemical studies of pellicle biofilms from subsurface acid mine drainage streams have shown abundant cytochromes from the dominant organism, Leptospirillum Group II. These cytochromes are proposed to be key proteins in aerobic Fe(II) oxidation, the dominant mode of cellular energy generation by the biofilms. In this study, we determined that posttranslational modification and expression of amino-acid sequence variants change as a function of biofilm maturation. For Cytochrome₅₇₉ (Cyt₅₇₉), the most abundant cytochrome in the biofilms, late developmental-stage biofilms differed from early-stage biofilms in N-terminal truncations and decreased redox potentials. Expression of sequence variants of two monoheme c-type cytochromes also depended on biofilm development. For Cyt(572), an abundant membrane-bound cytochrome, the expression of multiple sequence variants was observed in both early and late developmental-stage biofilms; however, redox potentials of Cyt₅₇₂ from these different sources did not vary significantly. These cytochrome analyses show a complex response of the Leptospirillum Group II electron transport chain to growth within a microbial community and illustrate the power of multiple proteomics techniques to define biochemistry in natural systems.
    Full-text · Article · Nov 2010 · The ISME Journal
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