DNA microarray analysis of the hyperthermophilic archaeon Pyrococcus furiosus: evidence for anNew type of sulfur-reducing enzyme complex

Formate and hydrogen in hydrothermal vents and their use by extremely thermophilic methanogens and heterotrophs

Extremely thermophilic methanogens in the Methanococci and heterotrophs in the Thermococci are common in deep-sea hydrothermal vents. All Methanococci use H₂ as an electron donor, and a few species can also use formate. Most Methanococci have a coenzyme F₄₂₀-reducing formate dehydrogenase. All Thermococci reduce S⁰ but have hydrogenases and produce H₂ in the absence of S⁰. Some Thermococci have formate hydrogenlyase (Fhl) that reversibly converts H₂ and CO₂ to formate or an NAD(P)⁺-reducing formate dehydrogenase (Nfd). Questions remain if Methanococci or Thermococci use or produce formate in nature, why only certain species can grow on or produce formate, and what the physiological role of formate is? Formate forms abiotically in hydrothermal fluids through chemical equilibrium with primarily H₂, CO₂, and CO and is strongly dependent upon H₂ concentration, pH, and temperature. Formate concentrations are highest in hydrothermal fluids where H₂ concentrations are also high, such as in ultramafic systems where serpentinization reactions occur. In nature, Methanococci are likely to use formate as an electron donor when H₂ is limiting. Thermococci with Fhl likely convert H₂ and CO₂ to formate when H₂ concentrations become inhibitory for growth. They are unlikely to grow on formate in nature unless formate is more abundant than H₂ in the environment. Nearly all Methanococci and Thermococci have a gene for at least one formate dehydrogenase catalytic subunit, which may be used to provide free formate for de novo purine biosynthesis. However, only species with a membrane-bound formate transporter can grow on or secrete formate. Interspecies H₂ transfer occurs between Thermococci and Methanococci. This and putative interspecies formate transfer may support Methanococci in low H₂ environments, which in turn may prevent growth inhibition of Thermococci by its own H₂. Future research directions include understanding when, where, and how formate is used and produced by these organisms in nature, and how transcription of Thermococci genes encoding formate-related enzymes are regulated.

Obligately aerobic human gut microbe expresses an oxygen resistant tungsten-containing oxidoreductase for detoxifying gut aldehydes

Brevibacillus massiliensis strain phR is an obligately aerobic microbe that was isolated from human feces. Here, we show that it readily takes up tungsten (W), a metal previously associated only with anaerobes. The W is incorporated into an oxidoreductase enzyme (BmWOR) that was purified from native biomass. BmWOR consists of a single 65 kDa subunit and contains a single W-pyranopterin cofactor and a single [4Fe-4S] cluster. It exhibited high aldehyde-oxidizing activity with very high affinities (apparent K_m < 6 μM) for aldehydes common in the human gut and in cooked foods, including furfural, propionaldehyde, benzaldehyde and tolualdehyde, suggesting that BmWOR plays a key role in their detoxification. B. massiliensis converted added furfural to furoic acid when grown in the presence of W, but not in the presence of the analogous element molybdenum. B. massiliensis ferredoxin (BmFd) served as the electron acceptor (apparent K_m < 5 μM) for BmWOR suggesting it is the physiological electron carrier. Genome analysis revealed a Fd-dependent rather than NADH-dependent Complex I, suggesting that WOR not only serves a detoxification role but its aldehyde substrates could also serve as a source of energy. BmWOR is the first tungstoenzyme and the first member of the WOR family to be obtained from a strictly aerobic microorganism. Remarkably, BmWOR oxidized furfural in the presence of air (21% O₂, v/v) but only if BmFd was also present. BmWOR is the first characterized member of the Clade 83 WORs, which are predominantly found in extremely halophilic and aerobic archaea (Clade 83A), with many isolated from food sources, while the remaining bacterial members (Clade 83B) include both aerobes and anaerobes. The potential advantages for microbes found in foods and involved in human gut health that harbor O₂-resistant WORs, including in Bacillus and Brevibacillus based-probiotics, are discussed.

Into the darkness: the ecologies of novel 'microbial dark matter' phyla in an Antarctic lake

Uncultivated microbial clades ('microbial dark matter') are inferred to play important but uncharacterized roles in nutrient cycling. Using Antarctic lake (Ace Lake, Vestfold Hills) metagenomes, 12 metagenome-assembled genomes (MAGs; 88%-100% complete) were generated for four 'dark matter' phyla: six MAGs from Candidatus Auribacterota (=Aureabacteria, SURF-CP-2), inferred to be hydrogen- and sulfide-producing fermentative heterotrophs, with individual MAGs encoding bacterial microcompartments (BMCs), gas vesicles, and type IV pili; one MAG (100% complete) from Candidatus Hinthialibacterota (=OLB16), inferred to be a facultative anaerobe capable of dissimilatory nitrate reduction to ammonia, specialized for mineralization of complex organic matter (e.g. sulfated polysaccharides), and encoding BMCs, flagella, and Tad pili; three MAGs from Candidatus Electryoneota (=AABM5-125-24), previously reported to include facultative anaerobes capable of dissimilatory sulfate reduction, and here inferred to perform sulfite oxidation, reverse tricarboxylic acid cycle for autotrophy, and possess numerous proteolytic enzymes; two MAGs from Candidatus Lernaellota (=FEN-1099), inferred to be capable of formate oxidation, amino acid fermentation, and possess numerous enzymes for protein and polysaccharide degradation. The presence of 16S rRNA gene sequences in public metagenome datasets (88%-100% identity) suggests these 'dark matter' phyla contribute to sulfur cycling, degradation of complex organic matter, ammonification and/or chemolithoautotrophic CO2 fixation in diverse global environments.

Characterization of membrane-bound sulfane reductase: A missing link in the evolution of modern day respiratory complexes

Hyperthermophilic archaea contain a hydrogen gas-evolving,respiratory membrane-bound NiFe-hydrogenase (MBH) that is very closely related to the aerobic respiratory complex I. During growth on elemental sulfur (S°), these microorganisms also produce a homologous membrane-bound complex (MBX), which generates H₂S. MBX evolutionarily links MBH to complex I, but its catalytic function is unknown. Herein, we show that MBX reduces the sulfane sulfur of polysulfides by using ferredoxin (Fd) as the electron donor, and we rename it membrane-bound sulfane reductase (MBS). Two forms of affinity-tagged MBS were purified from genetically engineered Pyrococcus furiosus (a hyperthermophilic archaea species): the 13-subunit holoenzyme (S-MBS) and a cytoplasmic 4-subunit catalytic subcomplex (C-MBS). S-MBS and C-MBS reduced dimethyl trisulfide (DMTS) with comparable K_m (∼490 μm) and V _max values (12 μmol/min/mg). The MBS catalytic subunit (MbsL), but not that of complex I (NuoD), retains two of four NiFe-coordinating cysteine residues of MBH. However, these cysteine residues were not involved in MBS catalysis because a mutant P. furiosus strain (MbsLC85A/C385A) grew normally with S°. The products of the DMTS reduction and properties of polysulfides indicated that in the physiological reaction, MBS uses Fd (E _o' = -480 mV) to reduce sulfane sulfur (E _o' -260 mV) and cleave organic (RS _n R, n ≥ 3) and anionic polysulfides (S _n ^2-, n ≥ 4) but that it does not produce H₂S. Based on homology to MBH, MBS also creates an ion gradient for ATP synthesis. This work establishes the electrochemical reaction catalyzed by MBS that is intermediate in the evolution from proton- to quinone-reducing respiratory complexes.

A broader active site in Pyrococcus horikoshii CoA disulfide reductase accommodates larger substrates and reveals evidence of subunit asymmetry

Within the family of pyridine nucleotide disulfide oxidoreductase (PNDOR), enzymes are a group of single‐cysteine containing FAD‐dependent reductases that utilize a tightly bound coenzyme A to assist in the NAD(P)H‐dependent reduction of di‐, per‐, and polysulfide substrates in bacteria and archaea. For many of these homodimeric enzymes, it has proved difficult to determine the substrate specificity and metabolic function based on sequence and genome analysis alone. Coenzyme A‐disulfide reductase (CoADR) isolated from Pyrococcus horikoshii (phCoADR) reduces Co‐A per‐ and polysulfides, but, unlike other highly homologous members of this group, is a poor CoA disulfide reductase. The phCoADR structure has a narrower access channel for CoA substrates, which suggested that this restriction might be responsible for the enzyme's poor activity toward the bulky CoA disulfide substrate. To test this hypothesis, the substrate channel was widened by making four mutations along the channel wall (Y65A, Y66A, P67G, and H367G). The structure of the quadruple mutant shows a widened substrate channel, which is supported by a fourfold increase in k_cat for the NAD(P)H‐dependent reduction of CoA disulfide and enhanced activity toward the substrate at lower temperatures. Anaerobic titrations of the enzyme with NADH revealed a half‐site reactivity not observed with the wild‐type enzyme in which one subunit of the enzyme could be fully reduced to an EH₄ state, while the other remained in an EH₂ or EH₂·NADH state. These results suggest that for these closely related enzymes, substrate channel morphology is an important determinant of substrate specificity, and homology modeling will be the preferred technique for predicting function among PNDORs.

Biological iron-sulfur storage in a thioferrate-protein nanoparticle

Iron–sulfur clusters are ubiquitous in biology and function in electron transfer and catalysis. They are assembled from iron and cysteine sulfur on protein scaffolds. Iron is typically stored as iron oxyhydroxide, ferrihydrite, encapsulated in 12 nm shells of ferritin, which buffers cellular iron availability. Here we have characterized IssA, a protein that stores iron and sulfur as thioferrate, an inorganic anionic polymer previously unknown in biology. IssA forms nanoparticles reaching 300 nm in diameter and is the largest natural metalloprotein complex known. It is a member of a widely distributed protein family that includes nitrogenase maturation factors, NifB and NifX. IssA nanoparticles are visible by electron microscopy as electron-dense bodies in the cytoplasm. Purified nanoparticles appear to be generated from 20 nm units containing ∼6,400 Fe atoms and ∼170 IssA monomers. In support of roles in both iron–sulfur storage and cluster biosynthesis, IssA reconstitutes the [4Fe-4S] cluster in ferredoxin in vitro.

The biosynthesis of iron-sulfur clusters in anaerobic organisms has not been extensively investigated. Here, the authors identify and characterize a multi-subunit protein that stores iron and sulfur in thioferrate for the assembly of the clusters in Pyrococcus furiosus.

SurR is a master regulator of the primary electron flow pathways in the order Thermococcales

The sulfur response regulator, SurR, is among a handful of known redox-active transcriptional regulators. First characterized from the hyperthermophile Pyrococcus furiosus, it is unique to the archaeal order Thermococcales. P. furiosus has two modes of electron disposal. Hydrogen gas is produced when the organism is grown in the absence of elemental sulfur (S⁰ ) and H₂ S is produced when grown in its presence. Switching between these metabolic modes requires a rapid transcriptional response and this is orchestrated by SurR. We show here that deletion of SurR causes severely impaired growth in the absence of S⁰ since genes essential for H₂ metabolism are no longer activated. Conversely, a strain containing a constitutively active SurR variant displays a growth phenotype in the presence of S⁰ due to constitutive repression of S⁰ -responsive genes. During a metabolic shift initiated by addition of S⁰ to the growth medium, both strains demonstrate a de-regulation of genes involved in the SurR regulon, including hydrogenase and related S⁰ -responsive genes. These results demonstrate that SurR is a master regulator of electron flow within P. furiosus, likely affecting the pools of ferredoxin, NADPH and NADH, as well as influencing metabolic pathways and thiol/disulfide redox balance.

Role of Supercomputers in Bioinformatics

Due to the involvement of effective and client-friendly components (i.e. supercomputers), rapid data analysis is being accomplished. In Bioinformatics, it is expanding many areas of research such as genomics, proteomics, metabolomics, etc. Structure-based drug design is one of the major areas of research to cure human malady. This chapter initiates a discussion on supercomputing in sequence analysis with a detailed table summarizing the software and Web-based programs used for sequence analysis. A brief talk on the supercomputing in virtual screening is given where the databases like DOCK, ZINC, EDULISS, etc. are introduced. As the chapter transitions to the next phase, the intricacies of advanced Quantitative Structure-Activity Relationship technologies like Fragment-Based 2D QSAR, Multiple-Field 3D QSAR, and Amino Acid-Based Peptide Prediction are put forth in a manner similar to the concept of abstraction. The supercomputing in docking studies is stressed where docking software for Protein-Ligand docking, Protein-Protein docking, and Multi-Protein docking are provided. The chapter ends with the applications of supercomputing in widely used microarray data analysis.

Proteomic Insights into Sulfur Metabolism in the Hydrogen-Producing Hyperthermophilic Archaeon Thermococcus onnurineus NA1

The hyperthermophilic archaeon Thermococcus onnurineus NA1 has been shown to produce H₂ when using CO, formate, or starch as a growth substrate. This strain can also utilize elemental sulfur as a terminal electron acceptor for heterotrophic growth. To gain insight into sulfur metabolism, the proteome of T. onnurineus NA1 cells grown under sulfur culture conditions was quantified and compared with those grown under H₂-evolving substrate culture conditions. Using label-free nano-UPLC-MSE-based comparative proteomic analysis, approximately 38.4% of the total identified proteome (589 proteins) was found to be significantly up-regulated (≥1.5-fold) under sulfur culture conditions. Many of these proteins were functionally associated with carbon fixation, Fe-S cluster biogenesis, ATP synthesis, sulfur reduction, protein glycosylation, protein translocation, and formate oxidation. Based on the abundances of the identified proteins in this and other genomic studies, the pathways associated with reductive sulfur metabolism, H₂-metabolism, and oxidative stress defense were proposed. The results also revealed markedly lower expression levels of enzymes involved in the sulfur assimilation pathway, as well as cysteine desulfurase, under sulfur culture condition. The present results provide the first global atlas of proteome changes triggered by sulfur, and may facilitate an understanding of how hyperthermophilic archaea adapt to sulfur-rich, extreme environments.

Primary transcriptome map of the hyperthermophilic archaeon Thermococcus kodakarensis

Background

Prokaryotes have relatively small genomes, densely-packed with protein-encoding sequences. RNA sequencing has, however, revealed surprisingly complex transcriptomes and here we report the transcripts present in the model hyperthermophilic Archaeon, Thermococcus kodakarensis, under different physiological conditions.

Results

Sequencing cDNA libraries, generated from RNA isolated from cells under different growth and metabolic conditions has identified >2,700 sites of transcription initiation, established a genome-wide map of transcripts, and consensus sequences for transcription initiation and post-transcription regulatory elements. The primary transcription start sites (TSS) upstream of 1,254 annotated genes, plus 644 primary TSS and their promoters within genes, are identified. Most mRNAs have a 5'-untranslated region (5'-UTR) 10 to 50 nt long (median = 16 nt), but ~20% have 5'-UTRs from 50 to 300 nt long and ~14% are leaderless. Approximately 50% of mRNAs contain a consensus ribosome binding sequence. The results identify TSS for 1,018 antisense transcripts, most with sequences complementary to either the 5'- or 3'-region of a sense mRNA, and confirm the presence of transcripts from all three CRISPR loci, the RNase P and 7S RNAs, all tRNAs and rRNAs and 69 predicted snoRNAs. Two putative riboswitch RNAs were present in growing but not in stationary phase cells. The procedure used is designed to identify TSS but, assuming that the number of cDNA reads correlates with transcript abundance, the results also provide a semi-quantitative documentation of the differences in T. kodakarensis genome expression under different growth conditions and confirm previous observations of substrate-dependent specific gene expression. Many previously unanticipated small RNAs have been identified, some with relative low GC contents (≤50%) and sequences that do not fold readily into base-paired secondary structures, contrary to the classical expectations for non-coding RNAs in a hyperthermophile.

Conclusion

The results identify >2,700 TSS, including almost all of the primary sites of transcription initiation upstream of annotated genes, plus many secondary sites, sites within genes and sites resulting in antisense transcripts. The T. kodakarensis genome is small (~2.1 Mbp) and tightly packed with protein-encoding genes, but the transcriptomes established also contain many non-coding RNAs and predict extensive RNA-based regulation in this model Archaeon.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-684) contains supplementary material, which is available to authorized users.

Engineering hydrogen gas production from formate in a hyperthermophile by heterologous production of an 18-subunit membrane-bound complex

Biohydrogen gas has enormous potential as a source of reductant for the microbial production of biofuels, but its low solubility and poor gas mass transfer rates are limiting factors. These limitations could be circumvented by engineering biofuel production in microorganisms that are also capable of generating H2 from highly soluble chemicals such as formate, which can function as an electron donor. Herein, the model hyperthermophile, Pyrococcus furiosus, which grows optimally near 100 °C by fermenting sugars to produce H2, has been engineered to also efficiently convert formate to H2. Using a bacterial artificial chromosome vector, the 16.9-kb 18-gene cluster encoding the membrane-bound, respiratory formate hydrogen lyase complex of Thermococcus onnurineus was inserted into the P. furiosus chromosome and expressed as a functional unit. This enabled P. furiosus to utilize formate as well as sugars as an H2 source and to do so at both 80° and 95 °C, near the optimum growth temperature of the donor (T. onnurineus) and engineered host (P. furiosus), respectively. This accomplishment also demonstrates the versatility of P. furiosus for metabolic engineering applications.

Structure and substrate specificity of the pyrococcal coenzyme A disulfide reductases/polysulfide reductases (CoADR/Psr): implications for S(0)-based respiration and a sulfur-dependent antioxidant system in Pyrococcus

FAD and NAD(P)H-dependent coenzyme A disulfide reductases/polysulfide reductases (CoADR/Psr) have been proposed to be important for the reduction of sulfur and disulfides in the sulfur-reducing anaerobic hyperthermophiles Pyrococcus horikoshii and Pyrococcus furiosus; however, the form(s) of sulfur that the enzyme actually reduces are not clear. Here we determined the structure for the FAD- and coenzyme A-containing holoenzyme from P. horikoshii to 2.7 Å resolution and characterized its substrate specificity. The enzyme is relatively promiscuous and reduces a range of disulfide, persulfide, and polysulfide compounds. These results indicate that the likely in vivo substrates are NAD(P)H and di-, poly-, and persulfide derivatives of coenzyme A, although polysulfide itself is also efficiently reduced. The role of the enzyme in the reduction of elemental sulfur (S(8)) in situ is not, however, ruled out by these results, and the possible roles of this substrate are discussed. During aerobic persulfide reduction, rapid recycling of the persulfide substrate was observed, which is proposed to occur via sulfide oxidation by O(2) and/or H(2)O(2). As expected, this reaction disappears under anaerobic conditions and may explain observations by others that CoADR is not essential for S(0) respiration in Pyrococcus or Thermococcus but appears to participate in oxidative defense in the presence of S(0). When compared to the homologous Npsr enzyme from Shewanella loihica PV-4 and homologous enzymes known to reduce CoA disulfide, the phCoADR structure shows a relatively restricted substrate channel leading into the sulfur-reducing side of the FAD isoalloxazine ring, suggesting how this enzyme class may select for specific disulfide substrates.

Regulation of iron metabolism by Pyrococcus furiosus

Iron is an essential element for the hyperthermophilic archaeon Pyrococcus furiosus, and many of its iron-containing enzymes have been characterized. How iron assimilation is regulated, however, is unknown. The genome sequence contains genes encoding two putative iron-responsive transcription factors, DtxR and Fur. Global transcriptional profiles of the dtxR deletion mutant (ΔDTXR) and the parent strain under iron-sufficient and iron-limited conditions indicated that DtxR represses the expression of the genes encoding two putative iron transporters, Ftr1 and FeoAB, under iron-sufficient conditions. Under iron limitation, DtxR represses expression of the gene encoding the iron-containing enzyme aldehyde ferredoxin oxidoreductase and a putative ABC-type transporter. Analysis of the dtxR gene sequence indicated an incorrectly predicted translation start site, and the corrected full-length DtxR protein, in contrast to the truncated version, specifically bound to the promoters of ftr1 and feoAB, confirming its role as a transcription regulator. Expression of the gene encoding Ftr1 was dramatically upregulated by iron limitation, but no phenotype was observed for the ΔFTR1 deletion mutant under iron-limited conditions. The intracellular iron concentrations of ΔFTR1 and the parent strain were similar, suggesting that under the conditions tested, Ftr1 is not an essential iron transporter despite its response to iron. In contrast to DtxR, the Fur protein appears not to be a functional regulator in P. furiosus, since it did not bind to the promoters of any of the iron-regulated genes and the deletion mutant (ΔFUR) revealed no transcriptional responses to iron availability. DtxR is therefore the key iron-responsive transcriptional regulator in P. furiosus.

Chlorobaculum tepidum TLS displays a complex transcriptional response to sulfide addition

Chlorobaculum tepidum is a green sulfur bacterium (GSB) that is a model system for phototrophic sulfur oxidation. Despite over 2 decades of research, conspicuous gaps exist in our understanding of its electron donor metabolism and regulation. RNA sequencing (RNA-seq) was used to provide a global picture of the C. tepidum transcriptome during growth on thiosulfate as the sole electron donor and at time points following the addition of sulfide to such a culture. Following sulfide addition, 121 to 150 protein-coding genes displayed significant changes in expression depending upon the time point. These changes included a rapid decrease in expression of thiosulfate and elemental sulfur oxidation genes. Genes and gene loci with increased expression included CT1087, encoding a sulfide:quinone oxidoreductase required for growth in high sulfide concentrations; a polysulfide reductase-like complex operon, psrABC (CT0496 to CT0494); and, surprisingly, a large cluster of genes involved in iron acquisition. Finally, two genes that are conserved as a cassette in anaerobic bacteria and archaea, CT1276 and CT1277, displayed a strong increase in expression. The CT1277 gene product contains a DNA-binding domain, suggesting a role for it in sulfide-dependent gene expression changes.

Deletion strains reveal metabolic roles for key elemental sulfur-responsive proteins in Pyrococcus furiosus

Transcriptional and enzymatic analyses of Pyrococcus furiosus previously indicated that three proteins play key roles in the metabolism of elemental sulfur (S(0)): a membrane-bound oxidoreductase complex (MBX), a cytoplasmic coenzyme A-dependent NADPH sulfur oxidoreductase (NSR), and sulfur-induced protein A (SipA). Deletion strains, referred to as MBX1, NSR1, and SIP1, respectively, have now been constructed by homologous recombination utilizing the uracil auxotrophic COM1 parent strain (ΔpyrF). The growth of all three mutants on maltose was comparable without S(0), but in its presence, the growth of MBX1 was greatly impaired while the growth of NSR1 and SIP1 was largely unaffected. In the presence of S(0), MBX1 produced little, if any, sulfide but much more acetate (per unit of protein) than the parent strain, demonstrating that MBX plays a critical role in S(0) reduction and energy conservation. In contrast, comparable amounts of sulfide and acetate were produced by NSR1 and the parent strain, indicating that NSR is not essential for energy conservation during S(0) reduction. Differences in transcriptional responses to S(0) in NSR1 suggest that two sulfide dehydrogenase isoenzymes provide a compensatory NADPH-dependent S(0) reduction system. Genes controlled by the S(0)-responsive regulator SurR were not as highly regulated in MBX1 and NSR1. SIP1 produced the same amount of acetate but more sulfide than the parent strain. That SipA is not essential for growth on S(0) indicates that it is not required for detoxification of metal sulfides, as previously suggested. A model is proposed for S(0) reduction by P. furiosus with roles for MBX and NSR in bioenergetics and for SipA in iron-sulfur metabolism.

Natural competence in the hyperthermophilic archaeon Pyrococcus furiosus facilitates genetic manipulation: construction of markerless deletions of genes encoding the two cytoplasmic hydrogenases

In attempts to develop a method of introducing DNA into Pyrococcus furiosus, we discovered a variant within the wild-type population that is naturally and efficiently competent for DNA uptake. A pyrF gene deletion mutant was constructed in the genome, and the combined transformation and recombination frequencies of this strain allowed marker replacement by direct selection using linear DNA. We have demonstrated the use of this strain, designated COM1, for genetic manipulation. Using genetic selections and counterselections based on uracil biosynthesis, we generated single- and double-deletion mutants of the two gene clusters that encode the two cytoplasmic hydrogenases. The COM1 strain will provide the basis for the development of more sophisticated genetic tools allowing the study and metabolic engineering of this important hyperthermophile.

The elemental sulfur-responsive protein (SipA) from the hyperthermophilic archaeon Pyrococcus furiosus is regulated by sulfide in an iron-dependent manner

The gene (sipA) encoding the sulfur-induced protein A (PF2025) is highly upregulated during growth of Pyrococcus furiosus on elemental sulfur (S(0)). Expression of sipA is regulated by sulfide, the product of S(0) reduction, but in an iron-dependent manner. SipA is proposed to play a role in intracellular iron sulfide detoxification.

Oxidative stress protection and the repair response to hydrogen peroxide in the hyperthermophilic archaeon Pyrococcus furiosus and in related species

Pyrococcus furiosus is a shallow marine, anaerobic archaeon that grows optimally at 100 degrees C. Addition of H(2)O(2) (0.5 mM) to a growing culture resulted in the cessation of growth with a 2-h lag before normal growth resumed. Whole genome transcriptional profiling revealed that the main response occurs within 30 min of peroxide addition, with the up-regulation of 62 open reading frames (ORFs), 36 of which are part of 10 potential operons. More than half of the up-regulated ORFs are of unknown function, while some others encode proteins that are involved potentially in sequestering iron and sulfide, in DNA repair and in generating NADPH. This response is thought to involve primarily damage repair rather than protection, since cultures exposed to sub-toxic levels of H(2)O(2) were not more resistant to the subsequent addition of H(2)O(2) (0.5-5.0 mM). Consequently, there is little if any induced protective response to peroxide. The organism maintains a constitutive protective mechanism involving high levels of oxidoreductase-type enzymes such as superoxide reductase, rubrerythrin, and alkyl hydroperoxide reductase. Related hyperthermophiles contain homologs of the proteins involved in the constitutive protective mechanism but these organisms were more sensitive to peroxide than P. furiosus and lack several of its peroxide-responsive ORFs.

Metagenomes from high-temperature chemotrophic systems reveal geochemical controls on microbial community structure and function

The Yellowstone caldera contains the most numerous and diverse geothermal systems on Earth, yielding an extensive array of unique high-temperature environments that host a variety of deeply-rooted and understudied Archaea, Bacteria and Eukarya. The combination of extreme temperature and chemical conditions encountered in geothermal environments often results in considerably less microbial diversity than other terrestrial habitats and offers a tremendous opportunity for studying the structure and function of indigenous microbial communities and for establishing linkages between putative metabolisms and element cycling. Metagenome sequence (14–15,000 Sanger reads per site) was obtained for five high-temperature (>65°C) chemotrophic microbial communities sampled from geothermal springs (or pools) in Yellowstone National Park (YNP) that exhibit a wide range in geochemistry including pH, dissolved sulfide, dissolved oxygen and ferrous iron. Metagenome data revealed significant differences in the predominant phyla associated with each of these geochemical environments. Novel members of the Sulfolobales are dominant in low pH environments, while other Crenarchaeota including distantly-related Thermoproteales and Desulfurococcales populations dominate in suboxic sulfidic sediments. Several novel archaeal groups are well represented in an acidic (pH 3) Fe-oxyhydroxide mat, where a higher O₂ influx is accompanied with an increase in archaeal diversity. The presence or absence of genes and pathways important in S oxidation-reduction, H₂-oxidation, and aerobic respiration (terminal oxidation) provide insight regarding the metabolic strategies of indigenous organisms present in geothermal systems. Multiple-pathway and protein-specific functional analysis of metagenome sequence data corroborated results from phylogenetic analyses and clearly demonstrate major differences in metabolic potential across sites. The distribution of functional genes involved in electron transport is consistent with the hypothesis that geochemical parameters (e.g., pH, sulfide, Fe, O₂) control microbial community structure and function in YNP geothermal springs.

Hot Transcriptomics

DNA microarray technology allows for a quick and easy comparison of complete transcriptomes, resulting in improved molecular insight in fluctuations of gene expression. After emergence of the microarray technology about a decade ago, the technique has now matured and has become routine in many molecular biology laboratories. Numerous studies have been performed that have provided global transcription patterns of many organisms under a wide range of conditions. Initially, implementation of this high-throughput technology has lead to high expectations for ground breaking discoveries. Here an evaluation is performed of the insight that transcriptome analysis has brought about in the field of hyperthermophilic archaea. The examples that will be discussed have been selected on the basis of their impact, in terms of either biological insight or technological progress.

Identification of two [4Fe-4S]-cluster-containing hydro-lyases from Pyrococcus furiosus

The hyperthermophilic archaeon Pyrococcus furiosus is a strict anaerobe. It is therefore not expected to use the oxidative tricarboxylic acid (TCA) cycle for energy transduction. Nonetheless, its genome encodes more putative TCA cycle enzymes than the closely related Pyrococcus horikoshii and Pyrococcus abyssi, including an aconitase (PF0201). Furthermore, a two-subunit fumarase (PF1755 and PF1754) is encoded on the Pyr. furiosus genome. In the present study, these three genes were heterologously overexpressed in Escherichia coli to enable characterization of the enzymes. PF1755 and PF1754 were shown to form a [4Fe-4S]-cluster-containing heterodimeric enzyme, able to catalyse the reversible hydratation of fumarate. The aconitase PF0201 also contained an Fe-S cluster, and catalysed the conversion from citrate to isocitrate. The fumarase belongs to the class of two-subunit, [4Fe-4S]-cluster-containing fumarate hydratases exemplified by MmcBC from Pelotomaculum thermopropionicum; the aconitase belongs to the aconitase A family. Aconitase probably plays a role in amino acid synthesis when the organism grows on carbohydrates. However, the function of the seemingly metabolically isolated fumarase in Pyr. furiosus has yet to be established.

Characterization of a heat-stable enzyme possessing GTP-dependent RNA ligase activity from a hyperthermophilic archaeon, Pyrococcus furiosus

Using an expression protein library of a hyperthermophilic archaeon, Pyrococcus furiosus, we identified a gene (PF0027) that encodes a protein with heat-stable cyclic nucleotide phosphodiesterase (CPDase) activity. The PF0027 gene encoded a 21-kDa protein and an amino acid sequence that showed approximately 27% identity to that of the 2'-5' tRNA ligase protein, ligT (20 kDa), from Escherichia coli. We found that the purified PF0027 protein possessed GTP-dependent RNA ligase activity and that synthetic tRNA halves bearing 2',3'-cyclic phosphate and 5'-OH termini were substrates for the ligation reaction in vitro. GTP hydrolysis was not required for the reaction, and GTPgammaS enhanced the tRNA ligation activity of PF0027 protein, suggesting that the ligation step is regulated by a novel mechanism. In comparison to the strong CPDase activity of the PF0027 protein, the RNA ligase activity itself was quite weak, and the ligation product was unstable during in vitro reaction. Finally, we used NMR to determine the solution structure of the PF0027 protein and discuss the implications of our results in understanding the role of the PF0027 protein.

SurR: a transcriptional activator and repressor controlling hydrogen and elemental sulphur metabolism in Pyrococcus furiosus

This work describes the identification and characterization of SurR, Pyrococcus furiosus sulphur (S(0)) response regulator. SurR was captured from cell extract using promoter DNA of a hydrogenase operon that is downregulated in the primary response of P. furiosus to S(0), as revealed by DNA microarray experiments. SurR was validated as a sequence-specific DNA binding protein, and characterization of the SurR DNA binding motif GTTn(3)AAC led to the identification of several target genes that contain an extended motif in their promoters. A number of these were validated to contain upstream SurR binding sites. These SurR targets strongly correspond with open reading frames and operons both up- and downregulated in the primary response to S(0). In vitro transcription revealed that SurR is an activator for its own gene as well as for two hydrogenase operons whose expression is downregulated during the primary S(0) response; it is also a repressor for two genes upregulated during the primary S(0) response, one of which encodes the primary S(0)-reducing enzyme NAD(P)H sulphur reductase. Herein we give evidence for the role of SurR in both mediating the primary response to S(0) and controlling hydrogen production in P. furiosus.

Complete genome sequence of the anaerobic, protein-degrading hyperthermophilic crenarchaeon Desulfurococcus kamchatkensis

Desulfurococcus kamchatkensis is an anaerobic organotrophic hyperthermophilic crenarchaeon isolated from a terrestrial hot spring. Its genome consists of a single circular chromosome of 1,365,223 bp with no extrachromosomal elements. A total of 1,474 protein-encoding genes were annotated, among which 205 are exclusive for D. kamchatkensis. The search for a replication origin site revealed a single region coinciding with a global extreme of the nucleotide composition disparity curve and containing a set of crenarchaeon-type origin recognition boxes. Unlike in most archaea, two genes encoding homologs of the eukaryotic initiator proteins Orc1 and Cdc6 are located distantly from this site. A number of mobile elements are present in the genome, including seven transposons representing IS607 and IS200/IS605 families and multiple copies of miniature inverted repeat transposable elements. Two large clusters of regularly interspaced repeats are present; none of the spacer sequences matches known archaeal extrachromosomal elements, except one spacer matches the sequence of a resident gene of D. kamchatkensis. Many of the predicted metabolic enzymes are associated with the fermentation of peptides and sugars, including more than 30 peptidases with diverse specificities, a number of polysaccharide degradation enzymes, and many transporters. Consistently, the genome encodes both enzymes of the modified Embden-Meyerhof pathway of glucose oxidation and a set of enzymes needed for gluconeogenesis. The genome structure and content reflect the organism's nutritionally diverse, competitive natural environment, which is periodically invaded by viruses and other mobile elements.

Archaeal transcription: function of an alternative transcription factor B from Pyrococcus furiosus

The genome of the hyperthermophile archaeon Pyrococcus furiosus encodes two transcription factor B (TFB) paralogs, one of which (TFB1) was previously characterized in transcription initiation. The second TFB (TFB2) is unusual in that it lacks recognizable homology to the archaeal TFB/eukaryotic TFIIB B-finger motif. TFB2 functions poorly in promoter-dependent transcription initiation, but photochemical cross-linking experiments indicated that the orientation and occupancy of transcription complexes formed with TFB2 at the strong gdh promoter are similar to the orientation and occupancy of transcription complexes formed with TFB1. Initiation complexes formed by TFB2 display a promoter opening defect that can be bypassed with a preformed transcription bubble, suggesting a mechanism to explain the low TFB2 transcription activity. Domain swaps between TFB1 and TFB2 showed that the low activity of TFB2 is determined mainly by its N terminus. The low activity of TFB2 in promoter opening and transcription can be partially relieved by transcription factor E (TFE). The results indicate that the TFB N-terminal region, containing conserved Zn ribbon and B-finger motifs, is important in promoter opening and that TFE can compensate for defects in the N terminus through enhancement of promoter opening.

Impact of substrate glycoside linkage and elemental sulfur on bioenergetics of and hydrogen production by the hyperthermophilic archaeon Pyrococcus furiosus

Glycoside linkage (cellobiose versus maltose) dramatically influenced bioenergetics to different extents and by different mechanisms in the hyperthermophilic archaeon Pyrococcus furiosus when it was grown in continuous culture at a dilution rate of 0.45 h(-1) at 90 degrees C. In the absence of S(0), cellobiose-grown cells generated twice as much protein and had 50%-higher specific H(2) generation rates than maltose-grown cultures. Addition of S(0) to maltose-grown cultures boosted cell protein production fourfold and shifted gas production completely from H(2) to H(2)S. In contrast, the presence of S(0) in cellobiose-grown cells caused only a 1.3-fold increase in protein production and an incomplete shift from H(2) to H(2)S production, with 2.5 times more H(2) than H(2)S formed. Transcriptional response analysis revealed that many genes and operons known to be involved in alpha- or beta-glucan uptake and processing were up-regulated in an S(0)-independent manner. Most differentially transcribed open reading frames (ORFs) responding to S(0) in cellobiose-grown cells also responded to S(0) in maltose-grown cells; these ORFs included ORFs encoding a membrane-bound oxidoreductase complex (MBX) and two hypothetical proteins (PF2025 and PF2026). However, additional genes (242 genes; 108 genes were up-regulated and 134 genes were down-regulated) were differentially transcribed when S(0) was present in the medium of maltose-grown cells, indicating that there were different cellular responses to the two sugars. These results indicate that carbohydrate characteristics (e.g., glycoside linkage) have a major impact on S(0) metabolism and hydrogen production in P. furiosus. Furthermore, such issues need to be considered in designing and implementing metabolic strategies for production of biofuel by fermentative anaerobes.

Insights into the metabolism of elemental sulfur by the hyperthermophilic archaeon Pyrococcus furiosus: characterization of a coenzyme A- dependent NAD(P)H sulfur oxidoreductase

The hyperthermophilic archaeon Pyrococcus furiosus uses carbohydrates as a carbon source and produces acetate, CO2, and H2 as end products. When S(0) is added to a growing culture, within 10 min the rate of H2 production rapidly decreases and H(2)S is detected. After 1 hour cells contain high NADPH- and coenzyme A-dependent S(0) reduction activity (0.7 units/mg, 85 degrees C) located in the cytoplasm. The enzyme responsible for this activity was purified to electrophoretic homogeneity (specific activity, 100 units/mg) and is termed NAD(P)H elemental sulfur oxidoreductase (NSR). NSR is a homodimeric flavoprotein (M(r), 100,000) and is encoded by PF1186. This designation was previously assigned to the gene encoding an enzyme that reduces coenzyme A disulfide, which is a side reaction of NSR. Whole-genome DNA microarray and quantitative PCR analyses showed that the expression of NSR is up-regulated up to sevenfold within 10 min of S(0) addition. This primary response to S(0) also involves the up-regulation (>16-fold) of a 13-gene cluster encoding a membrane-bound oxidoreductase (MBX). The cluster encoding MBX is proposed to replace the homologous 14-gene cluster that encodes the ferredoxin-oxidizing, H2-evolving membrane-bound hydrogenase (MBH), which is down-regulated >12-fold within 10 min of S(0) addition. Although an activity for MBX could not be demonstrated, it is proposed to conserve energy by oxidizing ferredoxin and reducing NADP, which is used by NSR to reduce S(0). A secondary response to S(0) is observed 30 min after S(0) addition and includes the up-regulation of genes encoding proteins involved in amino acid biosynthesis and iron metabolism, as well as two so-called sulfur-induced proteins termed SipA and SipB. This novel S(0)-reducing system involving NSR and MBX has been found so far only in the heterotrophic Thermococcales and is in contrast to the cytochrome- and quinone-based S(0)-reducing system in autotrophic archaea and bacteria.

Computational prediction of genomic functional cores specific to different microbes

Computational and experimental attempts tried to characterize a universal core of genes representing the minimal set of functional needs for an organism. Based on the increasing number of available complete genomes, comparative genomics has concluded that the universal core contains < 50 genes. In contrast, experiments suggest a much larger set of essential genes (certainly more than several hundreds, even under the most restrictive hypotheses) that is dependent on the biological complexity and environmental specificity of the organism. Highly biased genes, which are generally also the most expressed in translationally biased organisms, tend to be over represented in the class of genes deemed to be essential for any given bacterial species. This association is far from perfect; nevertheless, it allows us to propose a new computational method to detect, to a certain extent, ubiquitous genes, nonorthologous genes, environment-specific genes, genes involved in the stress response, and genes with no identified function but highly likely to be essential for the cell. Most of these groups of genes cannot be identified with previously attempted computational and experimental approaches. The large variety of life-styles and the unusually detectable functional signals characterizing translationally biased organisms suggest using them as reference organisms to infer essentiality in other microbial species. The case of small parasitic genomes is discussed. Data issued by the analysis are compared with previous computational and experimental studies. Results are discussed both on methodological and biological grounds.

Structure of coenzyme A-disulfide reductase from Staphylococcus aureus at 1.54 A resolution

Coenzyme A (CoASH) replaces glutathione as the major low molecular weight thiol in Staphylococcus aureus; it is maintained in the reduced state by coenzyme A-disulfide reductase (CoADR), a homodimeric enzyme similar to NADH peroxidase but containing a novel Cys43-SSCoA redox center. The crystal structure of S. aureus CoADR has been solved using multiwavelength anomalous dispersion data and refined at a resolution of 1.54 A. The resulting electron density maps define the Cys43-SSCoA disulfide conformation, with Cys43-S(gamma) located at the flavin si face, 3.2 A from FAD-C4aF, and the CoAS- moiety lying in an extended conformation within a cleft at the dimer interface. A well-ordered chloride ion is positioned adjacent to the Cys43-SSCoA disulfide and receives a hydrogen bond from Tyr361'-OH of the complementary subunit, suggesting a role for Tyr361' as an acid-base catalyst during the reduction of CoAS-disulfide. Tyr419'-OH is located 3.2 A from Tyr361'-OH as well and, based on its conservation in known functional CoADRs, also appears to be important for activity. Identification of residues involved in recognition of the CoAS-disulfide substrate and in formation and stabilization of the Cys43-SSCoA redox center has allowed development of a CoAS-binding motif. Bioinformatics analyses indicate that CoADR enzymes are broadly distributed in both bacterial and archaeal kingdoms, suggesting an even broader significance for the CoASH/CoAS-disulfide redox system in prokaryotic thiol/disulfide homeostasis.

Microarray analysis of the hyperthermophilic archaeon Pyrococcus furiosus exposed to gamma irradiation

The remarkable survival of the hyperthermophilic archaeon Pyrococcus furiosus to ionizing radiation was previously demonstrated. Using a time course study and whole-genome microarray analyses of mRNA transcript levels, the genes and regulatory pathways involved in the repair of lesions produced by ionizing irradiation (oxidative damage and DNA strand breaks) in P. furiosus were investigated. Data analyses showed that radA, encoding the archaeal homolog of the RecA/Rad51 recombinase, was moderately up regulated by irradiation and that a putative DNA-repair gene cluster was specifically induced by exposure to ionizing radiation. This novel repair system appears to be unique to thermophilic archaea and bacteria and is suspected to be involved in translesion synthesis. Genes that encode for a putative Dps-like iron-chelating protein and two membrane-bound oxidoreductases were differentially expressed following gamma irradiation, potentially in response to oxidative stress. Surprisingly, the many systems involved in oxygen detoxification and redox homeostasis appeared to be constitutively expressed. Finally, we identified several transcriptional regulators and protein kinases highly regulated in response to gamma irradiation.

Identification of a glycolytic regulon in the archaeaPyrococcusandThermococcus

The glycolytic pathway of the hyperthermophilic archaea that belong to the order Thermococcales (Pyrococcus, Thermococcus and Palaeococcus) differs significantly from the canonical Embden-Meyerhof pathway in bacteria and eukarya. This archaeal glycolysis variant consists of several novel enzymes, some of which catalyze unique conversions. Moreover, the enzymes appear not to be regulated allosterically, but rather at transcriptional level. To elucidate details of the gene expression control, the transcription initiation sites of the glycolytic genes in Pyrococcus furiosus have been mapped by primer extension analysis and the obtained promoter sequences have been compared with upstream regions of non-glycolytic genes. Apart from consensus sequences for the general transcription factors (TATA-box and BRE) this analysis revealed the presence of a potential transcription factor binding site (TATCAC-N(5)-GTGATA) in glycolytic and starch utilizing promoters of P. furiosus and several thermococcal species. The absence of this inverted repeat in Pyrococcus abyssi and Pyrococcus horikoshii probably reflects that their reduced catabolic capacity does not require this regulatory system. Moreover, this phyletic pattern revealed a TrmB-like regulator (PF0124 and TK1769) which may be involved in recognizing the repeat. This Thermococcales glycolytic regulon, with more than 20 genes, is the largest regulon that has yet been described for Archaea.

Production and characterization of a thermostable alcohol dehydrogenase that belongs to the aldo-keto reductase superfamily

The gene encoding a novel alcohol dehydrogenase that belongs to the aldo-keto reductase superfamily has been identified in the hyperthermophilic archaeon Pyrococcus furiosus. The gene, referred to as adhD, was functionally expressed in Escherichia coli and subsequently purified to homogeneity. The enzyme has a monomeric conformation with a molecular mass of 32 kDa. The catalytic activity of the enzyme increases up to 100 degrees C, and a half-life value of 130 min at this temperature indicates its high thermostability. AdhD exhibits a broad substrate specificity with, in general, a preference for the reduction of ketones (pH optimum, 6.1) and the oxidation of secondary alcohols (pH optimum, 8.8). Maximal specific activities were detected with 2,3-butanediol (108.3 U/mg) and diacetyl-acetoin (22.5 U/mg) in the oxidative and reductive reactions, respectively. Gas chromatrography analysis indicated that AdhD produced mainly (S)-2-pentanol (enantiomeric excess, 89%) when 2-pentanone was used as substrate. The physiological role of AdhD is discussed.

Defining genes in the genome of the hyperthermophilic archaeon Pyrococcus furiosus: implications for all microbial genomes

The original genome annotation of the hyperthermophilic archaeon Pyrococcus furiosus contained 2,065 open reading frames (ORFs). The genome was subsequently automatically annotated in two public databases by the Institute for Genomic Research (TIGR) and the National Center for Biotechnology Information (NCBI). Remarkably, more than 500 of the originally annotated ORFs differ in size in the two databases, many very significantly. For example, more than 170 of the predicted proteins differ at their N termini by more than 25 amino acids. Similar discrepancies were observed in the TIGR and NCBI databases with the other archaeal and bacterial genomes examined. In addition, the two databases contain 60 (NCBI) and 221 (TIGR) ORFs not present in the original annotation of P. furiosus. In the present study we have experimentally assessed the validity of 88 previously unannotated ORFs. Transcriptional analyses showed that 11 of 61 ORFs examined were expressed in P. furiosus when grown at either 95 or 72 degrees C. In addition, 7 of 54 ORFs examined yielded heat-stable recombinant proteins when they were expressed in Escherichia coli, although only one of the seven ORFs was expressed in P. furiosus under the growth conditions tested. It is concluded that the P. furiosus genome contains at least 17 ORFs not previously recognized in the original annotation. This study serves to highlight the discrepancies in the public databases and the problems of accurately defining the number and sizes of ORFs within any microbial genome.

Metabolic and evolutionary relationships among Pyrococcus Species: genetic exchange within a hydrothermal vent environment

Pyrococcus furiosus and Pyrococcus woesei grow optimally at temperatures near 100 degrees C and were isolated from the same shallow marine volcanic vent system. Hybridization of genomic DNA from P. woesei to a DNA microarray containing all 2,065 open reading frames (ORFs) annotated in the P. furiosus genome, in combination with PCR analysis, indicated that homologs of 105 ORFs present in P. furiosus are absent from the uncharacterized genome of P. woesei. Pulsed-field electrophoresis indicated that the sizes of the two genomes are comparable, and the results were consistent with the hypothesis that P. woesei lacks the 105 ORFs found in P. furiosus. The missing ORFs are present in P. furiosus mainly in clusters. These clusters include one cluster (Mal I, PF1737 to PF1751) involved in maltose metabolism and another cluster (PF0691 to PF0695) whose products are thought to remove toxic reactive nitrogen species. Accordingly, it was found that P. woesei, in contrast to P. furiosus, is unable to utilize maltose as a carbon source for growth, and the growth of P. woesei on starch was inhibited by addition of a nitric oxide generator. In P. furiosus the ORF clusters not present in P. woesei are bracketed by or are in the vicinity of insertion sequences or long clusters of tandem repeats (LCTRs). While the role of LCTRs in lateral gene transfer is not known, the Mal I cluster in P. furiosus is a composite transposon that undergoes replicative transposition. The same locus in P. woesei lacks any evidence of insertion activity, indicating that P. woesei is a sister or even the parent of P. furiosus. P. woesei may have acquired by lateral gene transfer more than 100 ORFs from other organisms living in the same thermophilic environment to produce the type strain of P. furiosus.

Heat shock response of Archaeoglobus fulgidus

The heat shock response of the hyperthermophilic archaeon Archaeoglobus fulgidus strain VC-16 was studied using whole-genome microarrays. On the basis of the resulting expression profiles, approximately 350 of the 2,410 open reading frames (ORFs) (ca. 14%) exhibited increased or decreased transcript abundance. These span a range of cell functions, including energy production, amino acid metabolism, and signal transduction, where the majority are uncharacterized. One ORF called AF1298 was identified that contains a putative helix-turn-helix DNA binding motif. The gene product, HSR1, was expressed and purified from Escherichia coli and was used to characterize specific DNA recognition regions upstream of two A. fulgidus genes, AF1298 and AF1971. The results indicate that AF1298 is autoregulated and is part of an operon with two downstream genes that encode a small heat shock protein, Hsp20, and cdc48, an AAA+ ATPase. The DNase I footprints using HSR1 suggest the presence of a cis-binding motif upstream of AF1298 consisting of CTAAC-N5-GTTAG. Since AF1298 is negatively regulated in response to heat shock and encodes a protein only distantly related to the N-terminal DNA binding domain of Phr of Pyrococcus furiosus, these results suggest that HSR1 and Phr may belong to an evolutionarily diverse protein family involved in heat shock regulation in hyperthermophilic and mesophilic Archaea organisms.

Insights on the evolution of metabolic networks of unicellular translationally biased organisms from transcriptomic data and sequence analysis

Codon bias is related to metabolic functions in translationally biased organisms, and two facts are argued about. First, genes with high codon bias describe in meaningful ways the metabolic characteristics of the organism; important metabolic pathways corresponding to crucial characteristics of the lifestyle of an organism, such as photosynthesis, nitrification, anaerobic versus aerobic respiration, sulfate reduction, methanogenesis, and others, happen to involve especially biased genes. Second, gene transcriptional levels of sets of experiments representing a significant variation of biological conditions strikingly confirm, in the case of Saccharomyces cerevisiae, that metabolic preferences are detectable by purely statistical analysis: the high metabolic activity of yeast during fermentation is encoded in the high bias of enzymes involved in the associated pathways, suggesting that this genome was affected by a strong evolutionary pressure that favored a predominantly fermentative metabolism of yeast in the wild. The ensemble of metabolic pathways involving enzymes with high codon bias is rather well defined and remains consistent across many species, even those that have not been considered as translationally biased, such as Helicobacter pylori, for instance, reveal some weak form of translational bias for this genome. We provide numerical evidence, supported by experimental data, of these facts and conclude that the metabolic networks of translationally biased genomes, observable today as projections of eons of evolutionary pressure, can be analyzed numerically and predictions of the role of specific pathways during evolution can be derived. The new concepts of Comparative Pathway Index, used to compare organisms with respect to their metabolic networks, and Evolutionary Pathway Index, used to detect evolutionarily meaningful bias in the genetic code from transcriptional data, are introduced.

Determination of coenzyme A levels in Pyrococcus furiosus and other Archaea: implications for a general role for coenzyme A in thermophiles

Physiologically significant levels of intracellular coenzyme A were identified in Pyrococcus furiosus, Thermococcus litoralis, and Sulfolobus solfataricus, suggesting a role for CoA as an important low molecular mass thiol in the thermophilic Archaea. In P. furiosus, cells grown in the presence of sulfur showed significantly higher levels of oxidized CoA compared with those grown in the absence of S(0). T. litoralis showed strikingly similar CoA levels, although with low disulfide levels in both the presence and absence of S(0). S. solfataricus showed similarly high levels of CoA thiol, with correspondingly low levels of the CoA disulfide. These results are consistent with the identification of a coenzyme A disulfide reductase (CoADR) in P. furiosus and horikoshii as well as the presence of CoADR homologues in the genomes of S. solfataricus and T. kodakaraensis.

Minimal sulfur requirement for growth and sulfur-dependent metabolism of the hyperthermophilic archaeon Staphylothermus marinus

Staphylothermus marinus is an anaerobic hyperthermophilic archaeon that uses peptides as carbon and energy sources. Elemental sulfur (S(o)) is obligately required for its growth and is reduced to H2S. The metabolic functions and mechanisms of S(o) reduction were explored by examining S(o)-dependent growth and activities of key enzymes present in this organism. All three forms of S(o) tested--sublimed S(o), colloidal S(o) and polysulfide--were used by S. marinus, and no other sulfur-containing compounds could replace S(o). Elemental sulfur did not serve as physical support but appeared to function as an electron acceptor. The minimal S(o) concentration required for optimal growth was 0.05% (w/v). At this concentration, there appeared to be a metabolic transition from H2 production to S reduction. Some enzymatic activities related to S(o)-dependent metabolism, including sulfur reductase, hydrogenase, glutamate dehydrogenase and electron transfer activities, were detected in cell-free extracts of S. marinus. These results indicate that S(o) plays an essential role in the heterotrophic metabolism of S. marinus. Reducing equivalents generated by the oxidation of amino acids from peptidolysis may be transferred to sulfur reductase and hydrogenase, which then catalyze the production of H2S and H2, respectively.

Discovery and characterization of a Coenzyme A disulfide reductase from Pyrococcus horikoshii. Implications for this disulfide metabolism of anaerobic hyperthermophiles

We have cloned NADH oxidase homologues from Pyrococcus horikoshii and P. furiosus, and purified the recombinant form of the P. horikoshii enzyme to homogeneity from Escherichia coli. Both enzymes (previously referred to as NOX2) have been shown to act as a coenzyme A disulfide reductases (CoADR: CoA-S-S-CoA + NAD(P)H + H+-->2CoA-SH + NAD(P)+). The P. horikoshii enzyme shows a kcat app of 7.2 s(-1) with NADPH at 75 degrees C. While the enzyme shows a preference for NADPH, it is able to use both NADPH and NADH efficiently, with both giving roughly equal kcats, while the Km for NADPH is roughly eightfold lower than that for NADH. The enzyme is specific for the CoA disulfide, and does not show significant reductase activity with other disulfides, including dephospho-CoA. Anaerobic reductive titration of the enzyme with NAD(P)H proceeds in two stages, with an apparent initial reduction of a nonflavin redox center with the first reduction resulting in what appears to be an EH2 form of the enzyme. Addition of a second of NADPH results in the formation of an apparent FAD-NAD(P)H complex. The behavior of this enzyme is quite different from the mesophilic staphylococcal version of the enzyme. This is only the second enzyme with this activity discovered, and the first from a strict anaerobe, an Archaea, or hyperthermophilic source. P. furiosus cells were assayed for small molecular mass thiols and found to contain 0.64 micromol CoA.g dry weight(-1) (corresponding to 210 microM CoA in the cell) consistent with CoA acting as a pool of disulfide reducing equivalents.

Cold shock of a hyperthermophilic archaeon: Pyrococcus furiosus exhibits multiple responses to a suboptimal growth temperature with a key role for membrane-bound glycoproteins

The hyperthermophilic archaeon, Pyrococcus furiosus, was grown on maltose near its optimal growth temperature, 95 degrees C, and at the lower end of the temperature range for significant growth, 72 degrees C. In addition, cultures were shocked by rapidly dropping the temperature from 95 to 72 degrees C. This resulted in a 5-h lag phase, during which time little growth occurred. Transcriptional analyses using whole-genome DNA microarrays representing 2,065 open reading frames (ORFs) in the P. furiosus genome showed that cells undergo three very different responses at 72 degrees C: an early shock (1 to 2 h), a late shock (5 h), and an adapted response (occurring after many generations at 72 degrees C). Each response involved the up-regulation in the expression of more than 30 ORFs unique to that response. These included proteins involved in translation, solute transport, amino acid biosynthesis, and tungsten and intermediary carbon metabolism, as well as numerous conserved-hypothetical and/or membrane-associated proteins. Two major membrane proteins were evident after one-dimensional sodium dodecyl sulfate-gel analysis of cold-adapted cells, and staining revealed them to be glycoproteins. Their cold-induced expression evident from the DNA microarray analysis was confirmed by quantitative PCR. Termed CipA (PF0190) and CipB (PF1408), both appear to be solute-binding proteins. While the archaea do not contain members of the bacterial cold shock protein (Csp) family, they all contain homologs of CipA and CipB. These proteins are also related phylogenetically to some cold-responsive genes recently identified in certain bacteria. The Cip proteins may represent a general prokaryotic-type cold response mechanism that is present even in hyperthermophilic archaea.