In addition to the ecological and evolutionary interest, hyperthermophile organisms are rapidly identified as potential sources of stable biomolecules having potential application in industrial processes. An understanding of their growth characteristics and metabolism is necessary to realize their full biotechnological potential.
The most extreme hyperthermophiles live on the superheated walls of deep-sea hydrothermal vents, requiring temperatures of at least 90 °C for survival. An extraordinary heat-tolerant hyperthermophile is Strain 121, which has been able to double its population during 24 hours in an autoclave at 121 °C (hence its name).
Hyperthermophiles have also been isolated from hot industrial environments (e.g., the outflow of geothermal power plants and sewage sludge systems). Deep-sea hyperthermophiles thrive in environments with hydrostatic pressures ranging from 200 to 360 atm.
While most pure hyperthermophilic enzymes are intrinsically very stable, some intracellular hyperthermophilic proteins get their high thermostability from intracellular environmental factors such as salts, high protein concentrations, coenzymes, substrates, activators, polyamines, or an extracellular environmental factor such as pressure.
From these studies, the highest optimal growth temperature for an organism is 105–106 °C ( Table 1).
Hyperthermophiles (mostly Archaea) grow optimally at temperatures above 80 °C with some representatives thriving even at 113 °C and higher ( Stetter, 2013 ). Occurrence of sulphate reduction at high temperature (above 100 °C) was shown by means of radio tracer ( 35 S-labelled sulphate) studies in hot deep-sea sediments retrieved from a hydrothermal vent site in the Guaymas Basin, Gulf of California ( Jørgensen, Isaksen, & Jannasch, 1992). The archaeal sulphate reducer A. fulgidus VC-16 T represents the first reported hyperthermophile among the SRP. The strain was isolated from hot sediments collected from a marine hydrothermal system at the Mediterranean island Vulcano (Italy) and displayed a Topt of 83 °C and Tmax of 92 °C ( Stetter et al., 1987 ). Research with A. fulgidus has primarily been concerned with the molecular understanding of adaptation to high temperature in the areas of dissimilatory sulphate reduction ( Parey, Fritz, et al., 2013 ), substrate uptake and ion exchange systems ( Andrade, Dickmanns, Ficner, & Einsle, 2005; Nishizawa et al., 2013), thermostability of biosynthetic enzymes (Yoneda, Sakuraba, Tsuge, Katunuma, & Ohshima, 2007 ), ether lipid biochemistry ( Lai, Springstead, & Monbouquette, 2008 ), genome-derived novel properties such as noncellulosomal cohesin ( Voronov-Goldman et al., 2011) and biogeochemically relevant sulphur isotope fractionation ( Mitchell, Heyer, Canfield, Hoek, & Habicht, 2009 ). The recently reported eubacterial Thermodesulfobacterium geofontis, isolated from Obsidian Pool (Yellowstone Park, USA), also qualifies as a hyperthermophile with a Topt 83 °C and a Tmax 90 °C ( Hamilton-Brehm et al., 2013). The supposedly sulphate-reducing crenarchaeote Caldivirga maquiligensis, isolated from an acidic hot spring in the Philippines and displaying a Topt 85 °C and a Tmax 92 °C ( Itoh et al., 1999 ), possesses a tri-split tRNA gene shedding new light on the evolution of fragmented tRNAs ( Fujishima et al., 2009 ).
Among the Crenarchaeota, Pyrodictium and Pyrolobus (order Igneococcales) are chemolithotrophic sulfur-dependent hyperthermophiles whose maximum growth temperatures of 110 and 113 °C, respectively, represent the upper temperature limits for life known so far. Pyrodictium is a strict anaerobe and grows on H 2 and S 0. Pyrolobus is unusual in that it is capable of reducing both NO 3 − and S 2 O 3 2 − to NH 4 + and H 2 S, respectively, with H 2 as the electron donor. Desulfurococcus and Staphylothermus (order Igneococcales) are phylogenetically clearly separate from the Pyrodictium group ( Figure 1 ). These coccoid or disc-shaped organisms have an optimal growth temperature higher than 85 °C and, in contrast with the Pyrodictium group, a maximum temperature not higher than 100 °C. They can grow chemolithoautotrophically by sulfur reduction to H 2 S or heterotrophically by sulfur respiration of various organic substrates. Thermoproteus and Thermofilum (order Thermoproteales) are rod-shaped hyperthermophiles that grow in mildly acidic conditions at temperatures up to 95 °C. They are both strict anaerobes that can grow chemolithotrophically on H 2 or chemoorganotrophically on complex carbon substrates with S 0 as an electron acceptor. Pyrobaculum aerophilum (order Thermoproteales) is a rod-shaped hyperthermophile capable of aerobic respiration in the presence of very low oxygen concentrations (∼0.3%) and nitrate reduction under strictly anaerobic conditions.
We analyzed two of these, Tk-subtilisin and Tk-SP. Subtilisins from mesophilic bacteria have been widely used in the detergent industry, because of broad substrate specificity and ease of large-scale preparation. Tk-subtilisin and Tk-SP are approximately 40% identical to these mesophilic bacterial subtilisins, and exhibit extraordinarily high stability compared with the mesophilic homologs. These two hyperthermophilic subtilisins are potential candidates for application in biotechnological fields, and will provide good models for the study of maturation and stabilization mechanisms in all subtilisin-like proteases.
Phr inhibits specifically cell-free transcription of its own gene and from promoters of genes of a small HSP, HSP20, and of an AAA + ATPase. The aaa+atpase and phr mRNA levels are induced after HS and during stationary growth phase in P. furiosus, indicating that the transcription of these genes is also affected by general stress and starvation. By contrast, the levels of the protein Phr are only slightly elevated during heat stress. In vitro experiments have shown that at high temperature (103 °C) Phr loses its functional conformation. The dissociation of the protein from its operator sequence may account for the high increase of phr mRNA levels detected after temperature upshift. Then, in Pyrococcus, there is a simple model for HS regulation: Phr binds promoter regions of HS genes at normothermic temperature inhibiting transcription by blocking RNAP recruitment. Subsequent release of Phr along with elevating temperature leads to activation of HS genes.
The heterotrophic archaea Hyperthermus butylicus and Pyrodictium abyssi have maximum growth temperatures of 108 and 110 °C, respectively. They grow on peptides and their growth is stimulated by the addition of H 2, CO 2, and S°.
Methanogens are more abundant in the colonic flora of mice with a genetic disposition for obesity.
An optimal temperature for the existence of hyperthermophiles is often above 80 °C (176 °F). Hyperthermophiles are often within the domain Archaea, although some bacteria are able to tolerate temperatures of around 100 °C (212 °F), as well. Some bacteria can live at temperatures higher than 100 °C at large depths in sea where water does not boil because of high pressure. Many hyperthermophiles are also able to withstand other environmental extremes such as high acidity or high radiation levels. Hyperthermophiles are a subset of extremophiles. Their existence may support the possibility of extraterrestrial life, as there is a higher heat range for life.
Since then, more than 70 species have been established. The most extreme hyperthermophiles live on the superheated walls of deep-sea hydrothermal vents, requiring temperatures of at least 90 °C for survival. An extraordinary heat-tolerant hyperthermophile is Strain 121, which has been able to double its population during 24 hours in an autoclave at 121 °C (hence its name). The current record growth temperature is 122 °C, for Methanopyrus kandleri .
The protein molecules in the hyperthermophiles exhibit hyperthermostability —that is, they can maintain structural stability (and therefore function) at high temperatures . Such proteins are homologous to their functional analogues in organisms which thrive at lower temperatures, but have evolved to exhibit optimal function at much greater temperatures. Most of the low-temperature homologues of the hyperthermostable proteins would be denatured above 60 °C. Such hyperthermostable proteins are often commercially important, as chemical reactions proceed faster at high temperatures.
The current record growth temperature is 122 °C, for Methanopyrus kandleri .
Geothermobacterium ferrireducens, which thrives in 65–100 °C in Obsidian Pool, Yellowstone National Park.
Some bacteria can live at temperatures higher than 100 °C at large depths in sea where water does not boil because of high pressure. Many hyperthermophiles are also able to withstand other environmental extremes such as high acidity or high radiation levels. Hyperthermophiles are a subset of extremophiles.
Early research into hyperthermophiles speculated that their genome could be characterized by high guanine-cytosine content; however, recent studies show that "there is no obvious correlation between the GC content of the genome and the optimal environmental growth temperature of the organism."
a. All extremophiles are in the Archaea domain.
c. The culture is not being kept at high temperatures.
c. Bacteria often have a symbiotic relationship with other organisms.
a. Hyperthermophils can survive only at very high temperatures that are difficult to replicate in a lab setting.
c. Hyperthermophils have a short life cycle, which makes it hard to study one particular organism.
1) (b) All Archaea are considered extremophiles. Explanation: All archaea are not extremophiles. Though they are most abundantly found in extreme environments like hot springs and salt lakes, but they h …. View the full answer.