Complete genome sequence of the thermophilic sulfate-reducing ocean bacterium Thermodesulfatator indicus type strain (CIR29812(T))

Characterization of the Pro101Gln mutation that enhances the catalytic performance of T. indicus NADH-dependent d-lactate dehydrogenase

NADH-dependent d-lactate dehydrogenases (d-LDH) are important for the industrial production of d-lactic acid. Here, we identify and characterize an improved d-lactate dehydrogenase mutant (d-LDH1) that contains the Pro101Gln mutation. The specific enzyme activities of d-LDH1 toward pyruvate and NADH are 21.8- and 11.0-fold greater compared to the wild-type enzyme. We determined the crystal structure of Apo-d-LDH1 at 2.65 Å resolution. Based on our structural analysis and docking studies, we explain the differences in activity with an altered binding conformation of NADH in d-LDH1. The role of the conserved residue Pro101 in d-LDH was further probed in site-directed mutagenesis experiments. We introduced d-LDH1 into Bacillus licheniformis yielding a d-lactic acid production of 145.9 g L-1 within 60 h at 50°C, which was three times higher than that of the wild-type enzyme. The discovery of d-LDH1 will pave the way for the efficient production of d-lactic acid by thermophilic bacteria.

Characterization of RNA-based and protein-only RNases P from bacteria encoding both enzyme types

A small group of bacteria encode two types of RNase P, the classical ribonucleoprotein (RNP) RNase P as well as the protein-only RNase P HARP (homolog of Aquifex RNase P). We characterized the dual RNase P activities of five bacteria that belong to three different phyla. All five bacterial species encode functional RNA (gene rnpB) and protein (gene rnpA) subunits of RNP RNase P, but only the HARP of the thermophile Thermodesulfatator indicus (phylum Thermodesulfobacteria) was found to have robust tRNA 5'-end maturation activity in vitro and in vivo in an Escherichia coli RNase P depletion strain. These findings suggest that both types of RNase P are able to contribute to the essential tRNA 5'-end maturation activity in T. indicus, thus resembling the predicted evolutionary transition state in the progenitor of the Aquificaceae before the loss of rnpA and rnpB genes in this family of bacteria. Remarkably, T. indicus RNase P RNA is transcribed with a P12 expansion segment that is posttranscriptionally excised in vivo, such that the major fraction of the RNA is fragmented and thereby truncated by ∼70 nt in the native T. indicus host as well as in the E. coli complementation strain. Replacing the native P12 element of T. indicus RNase P RNA with the short P12 helix of Thermotoga maritima RNase P RNA abolished fragmentation, but simultaneously impaired complementation efficiency in E. coli cells, suggesting that intracellular fragmentation and truncation of T. indicus RNase P RNA may be beneficial to RNA folding and/or enzymatic activity.

The plethora of membrane respiratory chains in the phyla of life

The diversity of microbial cells is reflected in differences in cell size and shape, motility, mechanisms of cell division, pathogenicity or adaptation to different environmental niches. All these variations are achieved by the distinct metabolic strategies adopted by the organisms. The respiratory chains are integral parts of those strategies especially because they perform the most or, at least, most efficient energy conservation in the cell. Respiratory chains are composed of several membrane proteins, which perform a stepwise oxidation of metabolites toward the reduction of terminal electron acceptors. Many of these membrane proteins use the energy released from the oxidoreduction reaction they catalyze to translocate charges across the membrane and thus contribute to the establishment of the membrane potential, i.e. they conserve energy. In this work we illustrate and discuss the composition of the respiratory chains of different taxonomic clades, based on bioinformatic analyses and on biochemical data available in the literature. We explore the diversity of the respiratory chains of Animals, Plants, Fungi and Protists kingdoms as well as of Prokaryotes, including Bacteria and Archaea. The prokaryotic phyla studied in this work are Gammaproteobacteria, Betaproteobacteria, Epsilonproteobacteria, Deltaproteobacteria, Alphaproteobacteria, Firmicutes, Actinobacteria, Chlamydiae, Verrucomicrobia, Acidobacteria, Planctomycetes, Cyanobacteria, Bacteroidetes, Chloroflexi, Deinococcus-Thermus, Aquificae, Thermotogae, Deferribacteres, Nitrospirae, Euryarchaeota, Crenarchaeota and Thaumarchaeota.

Thermodesulfatator autotrophicus sp. nov., a thermophilic sulfate-reducing bacterium from the Indian Ocean

A novel sulfate-reducing bacterium, strain S606T, was isolated from a sulfide sample collected at a depth of 2764 m from a deep-sea vent chimney wall in the Indian Ocean. Phylogenetic 16S rRNA gene sequence analyses placed strain S606T within the genus Thermodesulfatator, with highest sequence similarity of 98.2 % to Thermodesulfatator indicus DSM 15286T, followed by Thermodesulfatator atlanticus AT1325T (97.4 %). The average nucleotide identity (ANI) values between S606T and the two other type strains (T. indicus DSM 15286T and T. atlanticus AT1325T) were 79.2 % and 71.5 %, respectively. The digital DNA-DNA hybridization estimate values between S606T and these two type strains were 22.7±2.4 % and 18.1±2.3 %, respectively. Cells were Gram-stain-negative, anaerobic, motile rods (1-1.8×0.5-0.7 µm). The novel isolate grew at NaCl concentrations ranging from 1.5 to 4.5 % (optimum 2.5-3 %), from pH 5.5 to 8 (optimum 6.5-7.0) and at temperatures between 50 and 80 °C (optimum 65-70 °C). S606T grew chemolithoautotrophically in an H2/CO2 atmosphere (80 : 20, v/v; 200 kPa), used sulfate as a terminal electron acceptor, but not sulfur, sulfite nor thiosulfate. The predominant fatty acids were C16 : 0 (24.2 %), summed feature 8 (C18 : 1ω6c and/or C18 : 1ω7c, 26.3 %), C18 : 0 (22.2 %) and C18 : 1ω9c (9.2 %). The DNA G+C content of the chromosomal DNA was 43.1 mol%. The combined genotypic, chemotaxonomic and phenotypic traits show that S606T should be described as representing a novel species of the genus Thermodesulfatator, for which the name Thermodesulfatator autotrophicus sp. nov. is proposed. The type strain is S606T (=DSM 101864T=MCCC 1A01871T).

A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes

Dissimilatory sulphate reduction is the unifying and defining trait of sulphate-reducing prokaryotes (SRP). In their predominant habitats, sulphate-rich marine sediments, SRP have long been recognized to be major players in the carbon and sulphur cycles. Other, more recently appreciated, ecophysiological roles include activity in the deep biosphere, symbiotic relations, syntrophic associations, human microbiome/health and long-distance electron transfer. SRP include a high diversity of organisms, with large nutritional versatility and broad metabolic capacities, including anaerobic degradation of aromatic compounds and hydrocarbons. Elucidation of novel catabolic capacities as well as progress in the understanding of metabolic and regulatory networks, energy metabolism, evolutionary processes and adaptation to changing environmental conditions has greatly benefited from genomics, functional OMICS approaches and advances in genetic accessibility and biochemical studies. Important biotechnological roles of SRP range from (i) wastewater and off gas treatment, (ii) bioremediation of metals and hydrocarbons and (iii) bioelectrochemistry, to undesired impacts such as (iv) souring in oil reservoirs and other environments, and (v) corrosion of iron and concrete. Here we review recent advances in our understanding of SRPs focusing mainly on works published after 2000. The wealth of publications in this period, covering many diverse areas, is a testimony to the large environmental, biogeochemical and technological relevance of these organisms and how much the field has progressed in these years, although many important questions and applications remain to be explored.

Shifting the metallocentric molybdoenzyme paradigm: the importance of pyranopterin coordination

In this review, we test the hypothesis that pyranopterin coordination plays a critical role in defining substrate reactivities in the four families of mononuclear molybdenum and tungsten enzymes (Mo/W-enzymes). Enzyme families containing a single pyranopterin dithiolene chelate have been demonstrated to have reactivity towards two (sulfite oxidase, SUOX-fold) and five (xanthine dehydrogenase, XDH-fold) types of substrate, whereas the major family of enzymes containing a bis-pyranopterin dithiolene chelate (dimethylsulfoxide reductase, DMSOR-fold) is reactive towards eight types of substrate. A second bis-pyranopterin enzyme (aldehyde oxidoreductase, AOR-fold) family catalyzes a single type of reaction. The diversity of reactions catalyzed by each family correlates with active site variability, and also with the number of pyranopterins and their coordination by the protein. In the case of the AOR-fold enzymes, inflexibility of pyranopterin coordination correlates with their limited substrate specificity (oxidation of aldehydes). In examples of the SUOX-fold and DMSOR-fold enzymes, we observe three types of histidine-containing charge-transfer relays that can: (1) connect the piperazine ring of the pyranopterin to the substrate-binding site (SUOX-fold enzymes); (2) provide inter-pyranopterin communication (DMSOR-fold enzymes); and (3) connect a pyran ring oxygen to deeply buried water molecules (the DMSOR-fold NarGHI-type nitrate reductases). Finally, sequence data mining reveals a number of bacterial species whose predicted proteomes contain large numbers (up to 64) of Mo/W-enzymes, with the DMSOR-fold enzymes being dominant. These analyses also reveal an inverse correlation between Mo/W-enzyme content and pathogenicity.

Pan-genome analyses identify lineage- and niche-specific markers of evolution and adaptation in Epsilonproteobacteria

The rapidly increasing availability of complete bacterial genomes has created new opportunities for reconstructing bacterial evolution, but it has also highlighted the difficulty to fully understand the genomic and functional variations occurring among different lineages. Using the class Epsilonproteobacteria as a case study, we investigated the composition, flexibility, and function of its pan-genomes. Models were constructed to extrapolate the expansion of pan-genomes at three different taxonomic levels. The results show that, for Epsilonproteobacteria the seemingly large genome variations among strains of the same species are less noticeable when compared with groups at higher taxonomic ranks, indicating that genome stability is imposed by the potential existence of taxonomic boundaries. The analyses of pan-genomes has also defined a set of universally conserved core genes, based on which a phylogenetic tree was constructed to confirm that thermophilic species from deep-sea hydrothermal vents represent the most ancient lineages of Epsilonproteobacteria. Moreover, by comparing the flexible genome of a chemoautotrophic deep-sea vent species to (1) genomes of species belonging to the same genus, but inhabiting different environments, and (2) genomes of other vent species, but belonging to different genera, we were able to delineate the relative importance of lineage-specific versus niche-specific genes. This result not only emphasizes the overall importance of phylogenetic proximity in shaping the variable part of the genome, but also highlights the adaptive functions of niche-specific genes. Overall, by modeling the expansion of pan-genomes and analyzing core and flexible genes, this study provides snapshots on how the complex processes of gene acquisition, conservation, and removal affect the evolution of different species, and contribute to the metabolic diversity and versatility of Epsilonproteobacteria.

Molecular signatures for the phylum Aquificae and its different clades: proposal for division of the phylum Aquificae into the emended order Aquificales, containing the families Aquificaceae and Hydrogenothermaceae, and a new order Desulfurobacteriales ord. nov., containing the family Desulfurobacteriaceae

We report here detailed phylogenetic and comparative analyses on 11 sequenced genomes from the phylum Aquificae to identify molecular markers that are specific for the species from this phylum or its different families (viz. Aquificaceae, Hydrogenothermaceae and Desulfurobacteriaceae). In phylogenetic trees based on 16S rRNA gene or concatenated sequences for 32 conserved proteins, species from the three Aquificae families formed distinct clades. These trees also supported a strong relationship between the Aquificaceae and Hydrogenothermaceae families. In parallel, comparative analyses on protein sequences from Aquificae genomes have identified 46 conserved signature indels (CSIs) in broadly distributed proteins that are either exclusively or mainly found in members of the phylum Aquificae or its different families and subclades. Four of these CSIs, which are found in all sequenced Aquificae species, provide potential molecular markers for this phylum. Twelve, six and thirteen other CSIs that respectively are specific for the sequenced Aquificaceae, Hydrogenothermaceae and Desulfurobacteriaceae species provide molecular markers and novel tools for the identification of members of these families and for genetic and biochemical studies on them. Lastly, these studies have identified 11 CSIs in divergent proteins that are uniquely shared by members of the Aquificaceae and Hydrogenothermaceae families providing strong evidence that these two groups of bacteria shared a common ancestor exclusive of all other Aquificae (bacteria). The species from these two families are also very similar in their metabolic and physiological properties and they consist of aerobic or microaerophilic bacteria, which generally obtain energy by oxidation of hydrogen or reduced sulfur compounds by molecular oxygen. Based upon their strong association in phylogenetic trees, unique shared presence of large numbers of CSIs in different proteins, and similarities in their metabolic and physiological properties, it is proposed that the order Aquificales should be emended to include only the members of the families Aquificaceae and Hydrogenothermaceae. The members of the family Desulfurobacteriaceae, which are obligate anaerobes that strictly use hydrogen as electron donor, are now transferred to a new order Desulfurobacteriales ord. nov. The emended descriptions of the phylum Aquificae and its three families incorporating information for different molecular signatures are also provided.

Complete Genome Sequence of the Hyperthermophilic Sulfate-Reducing Bacterium Thermodesulfobacterium geofontis OPF15T

Thermodesulfobacterium geofontis OPF15^T (ATCC BAA-2454, JCM 18567) was isolated from Obsidian Pool, Yellowstone National Park, and grows optimally at 83°C. The 1.6-Mb genome sequence was finished at the Joint Genome Institute and has been deposited for future genomic studies pertaining to microbial processes and nutrient cycles in high-temperature environments.

A genomic approach to the cryptic secondary metabolome of the anaerobic world

A total of 211 complete and published genomes from anaerobic bacteria are analysed for the presence of secondary metabolite biosynthesis gene clusters, in particular those tentatively coding for polyketide synthases (PKS) and non-ribosomal peptide synthetases (NRPS). We investigate the distribution of these gene clusters according to bacterial phylogeny and, if known, correlate these to the type of metabolic pathways they encode. The potential of anaerobes as secondary metabolite producers is highlighted.