Enzymes synthesized by hyperthermophiles (bacteria and archaea with optimal growth temperatures of >80°C), also called hyperthermophilic enzymes, are typically thermostable (i.e., resistant to irreversible inactivation at high temperatures) and are optimally active at high temperatures. These enzymes share the same catalytic mechanisms with their mesophilic counterparts. When cloned and expressed in mesophilic hosts, hyperthermophilic enzymes usually retain their thermal properties, indicating that these properties are genetically encoded. Sequence alignments, amino acid content comparisons, crystal structure comparisons, and mutagenesis experiments indicate that hyperthermophilic enzymes are, indeed, very similar to their mesophilic homologues. No single mechanism is responsible for the remarkable stability of hyperthermophilic enzymes. Increased thermostability must be found, instead, in a small number of highly specific alterations that often do not obey any obvious traffic rules. After briefly discussing the diversity of hyperthermophilic organisms, this review concentrates on the remarkable thermostability of their enzymes. The biochemical and molecular properties of hyperthermophilic enzymes are described. Mechanisms responsible for protein inactivation are reviewed. The molecular mechanisms involved in protein thermostabilization are discussed, including ion pairs, hydrogen bonds, hydrophobic interactions, disulfide bridges, packing, decrease of the entropy of unfolding, and intersubunit interactions. Finally, current uses and potential applications of thermophilic and hyperthermophilic enzymes as research reagents and as catalysts for industrial processes are described.

Hyperthermophilic Enzymes: Sources, Uses, and Molecular Mechanisms for Thermostability

Nitrogen is an essential component of all living organisms and the main nutrient limiting life on our planet By far, the largest inventory of freely accessible nitrogen is atmospheric dinitrogen, but most organisms rely on more bioavailable forms of nitrogen, such as ammonium and nitrate, for growth The availability of these substrates depends on diverse nitrogen-transforming reactions that are carried out by complex networks of metabolically versatile microorganisms In this Review, we summarize our current understanding of the microbial nitrogen-cycling network, including novel processes, their underlying biochemical pathways, the involved microorganisms, their environmental importance and industrial applications

/pdf/the-microbial-nitrogen-cycling-network-2e26lf3i3f.pdf

The microbial nitrogen-cycling network

Each recent report of liquid water existing elsewhere in the Solar System has reverberated through the international press and excited the imagination of humankind. Why? Because in the past few decades we have come to realize that where there is liquid water on Earth, virtually no matter what the physical conditions, there is life. What we previously thought of as insurmountable physical and chemical barriers to life, we now see as yet another niche harbouring 'extremophiles'. This realization, coupled with new data on the survival of microbes in the space environment and modelling of the potential for transfer of life between celestial bodies, suggests that life could be more common than previously thought. Here we examine critically what it means to be an extremophile, and the implications of this for evolution, biotechnology and especially the search for life in the Universe.

/pdf/life-in-extreme-environments-qdlikt0yc0.pdf

Life in Extreme Environments

Archaeoglobus fulgidus is the first sulphur-metabolizing organism to have its genome sequence determined. Its genome of 2,178,400 base pairs contains 2,436 open reading frames (ORFs). The information processing systems and the biosynthetic pathways for essential components (nucleotides, amino acids and cofactors) have extensive correlation with their counterparts in the archaeon Methanococcus jannaschii. The genomes of these two Archaea indicate dramatic differences in the way these organisms sense their environment, perform regulatory and transport functions, and gain energy. In contrast to M. jannaschii, A. fulgidus has fewer restriction-modification systems, and none of its genes appears to contain inteins. A quarter (651 ORFs) of the A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs). Another quarter of the genome encodes new proteins indicating substantial archaeal gene diversity.

/pdf/the-complete-genome-sequence-of-the-hyperthermophilic-3q4yi248rf.pdf

The complete genome sequence of the hyperthermophilic, sulphate-reducing archaeon Archaeoglobus fulgidus

Chemistry of iron sulfides.

A novel, irregular, coccoid-shaped archaeum was isolated from a hydrothermally heated black smoker wall at the TAG site at the Mid Atlantic Ridge (depth 3650 meters). It grew at between 90 degrees C and 113 degrees C (optimum 106 degrees C) and pH 4.0-6.5 (optimum 5.5) and 1%-4% salt (optimum 1.7%). The organism was a facultatively aerobic obligate chemolithoautotroph gaining energy by H2-oxidation. Nitrate, S2O3(2-), and low concentrations of O2 (up to 0.3% v/v) served as electron acceptors, yielding NH4+, H2S, and H2O as end products, respectively. Growth was inhibited by acetate, pyruvate, glucose, starch, or sulfur. The new isolate was able to form colonies on plates (at 102 degrees C) and to grow at a pressure of 25000 kPa (250 bar). Exponentially growing cultures survived a one-hour autoclaving at 121 degrees C. The GC content was 53 mol%. The core lipids consisted of glycerol-dialkyl glycerol tetraethers and traces of 2,3-di-O-phytanyl-sn-glycerol. The cell wall was composed of a surface layer of tetrameric protein complexes arranged on a p4-lattice (center-to-center distance 18.5 nm). By its 16S rRNA sequence, the new isolate belonged to the Pyrodictiaceae. Based on its GC-content, DNA homology, S-layer composition, and metabolism, we describe here a new genus, which we name Pyrolobus (the "fire lobe"). The type species is Pyrolobus fumarii (type strain 1A; DSM 11204).

Pyrolobus fumarii, gen. and sp. nov., represents a novel group of archaea, extending the upper temperature limit for life to 113 degrees C

HOT springs and hydrothermal vents harbour hyperthermophilic archaea and bacteria with the highest growth temperatures known1–6. Here we report the discovery of high concentrations of hyperthermophiles in the production fluids from four oil reservoirs about 3,000 metres below the bed of the North Sea and below the permafrost surface of the North Slope of Alaska. Enrichment cultures of sulphidogens grew at 85 °C and 102 °C, which are similar to in situ reservoir temperatures7,8. Some species were identical to those from submarine hot vents and may have entered the reservoirs in injected sea water. Several enrichments grew anaerobically in sterilized artificial sea water with crude oil as the single carbon and energy source. These hyperthermophiles may be part of novel high-temperature communities and could be responsible for in situ bioconversions of crude oil fractions at temperatures previously considered too extreme for biochemical reactions4,7,9,10.

Hyperthermophilic archaea are thriving in deep North Sea and Alaskan oil reservoirs

Iron sulfide gives rise to unusual reducing reactions: some dependent on FeS/H2S synergism [NO-3 --> NH3; HC(three bonds)CH--> H2C=CH2, H3C-CH3; -CH2-CO- --> -CH=CH-, -CH2-CH2-; HS-CH2-COOH --> CH3-COOH; others dependent on FeS alone [HS-CH2-CH2-X --> CH2=CH2 (where X = OH, SH, or NH2)]. The experimental conditions are geochemically plausible: 100 degrees C, aqueous, nearly neutral, and fastidiously anaerobic. These reactions establish additional facts of soil chemistry, organic geochemistry, and the global nitrogen cycle. Further, they point to the common evolutionary denominator of geochemistry and biochemistry.

https://www.pnas.org/content/pnas/89/17/8117.full.pdf

Reactions depending on iron sulfide and linking geochemistry with biochemistry.

Hyperthermophilic Archaea and Bacteria with optimal growth temperatures between 80 and 110°C have been isolated from geo- and hydro-thermally heated terrestrial and submarine environments. 16S rRNA sequence comparisons indicate great phylogenetic diversity among the 23 different genera represented. Hyperthermophiles consist of anaerobic and aerobic chemolithoautotrophs and heterotrophs growing at neutral or acidic pH. Their outstanding heat resistance makes them as interesting objects for basic research as for biotechnology in the future.

Isolation, taxonomy and phylogeny of hyperthermophilic microorganisms.

Amide bonds are of central importance for biochemistry; in the guise of peptide bonds, they form the backbone of proteins. The formation of amide bonds without the assistance of enzymes poses a major challenge for theories of the origin of life. Enzyme-free formation of amide bonds between amino acids has been demonstrated in the presence of condensing agents such as cyanamide. Here we report the formation of amide bonds in aqueous solution in the absence of any condensing agent. We find that the formation of pyrite (FeS2) from FeS and H2S can provide the driving force for reductive acetylation of amino acids with mercaptoacetic acid (HSCH2COOH). The redox energy of pyrite formation permits the activation of the carboxylic acid group, which is converted to a species that reacts readily with amines. This process provides support for the chemo-autotrophic theory for the origin of life, in which pyrite formation supplies the energy source for the first autocatalytic reproduction cycle.

E. Blöchl

Papers

Pyrolobus fumarii, gen. and sp. nov., represents a novel group of archaea, extending the upper temperature limit for life to 113 degrees C

Hyperthermophilic archaea are thriving in deep North Sea and Alaskan oil reservoirs

Reactions depending on iron sulfide and linking geochemistry with biochemistry.

Isolation, taxonomy and phylogeny of hyperthermophilic microorganisms.

Formation of amide bonds without a condensation agent and implications for origin of life.