Everything you need to know about extremophiles. Some of the frequently asked questions are as follows:-
Q.1. What are extremophiles?
Ans. The extremophiles are the organisms which grow under extreme environmental conditions like temperature, salinity, pH, anaerobic conditions (sensitive to oxygen), extreme atmospheric pressure, water stress and others under which other organisms will generally not grow or the conditions that may kill other organisms.
The term ‘extremophile’ has generally not been used in the old literature as it came up with the discovery of a unique group of prokaryotes from extreme environments. It is from extreme environments. It is from Latin (extremus = extreme, and Greek phila = love or friend of)
The extremophiles include extreme psychrophilic (cold loving) extreme thermophiles, (heat loving) alkalophiles (bacteria that live at very high pH or alkaline conditions), acidophiles (microorganisms) which show preference for growth at low pH, approximately 2.0), methanogens (methane producing microorganisms) osmophiles (the organisms which grow optimally in or on media of high osmotic pressure), barophiles (atmospheric pressure lovers) and sulphur metabolizers. Archaeoglobus profundus a sulphur reducer bears optimum growth temperature of 82°C (Fig. 6.1)
Q.2. Which is the first extremophile to have its genome sequence?
Ans. The first extremophile to have its genome sequence was Methanococcus jannaschii, an archaeobacterium which lives near sea level where temperature reaches boiling point of waters and pressure enough to crush an ordinary submarine. These atmospheric pressure lovers are called barophiles. It exhibits high growth rate and high enzymatic activities at elevated temperatures.
Q.3. Name the organisms other than Archaeobacteria that come under extremophiles.
Ans. The Archaeobacteria alone do not come under extremophiles rather they include bacteria like Deinococcus radiodurans, Thermus aquaticus and Spirochaeta Americana and the animals Pompeii worm, psychrophilic Grydloblatlodeae (insects); Antarctic krill and water bear.
Q.4. Name a genus of cell wall-less Archaea.
Ans. Typical example of cell wall-less Archaea is the genus Thermoplasma, in which the cells range from spheres to filaments. The cytoplasmic membrane of cell of Thermoplasma are made of diglycerol tetra ethers with 40-carbon isoprenoid hydrocarbons. The species of Thermoplasma are thermopile and acidophilic growing optimally at about 60°C and pH 2. They like sulphur-metabolizing archaea under anaerobic conditions require sulphur and reduce that to hydrogen sulphide.
However, 16 S ribosomal RNA sequence homology points out that Thermoplasma is closely related to methanogen/halophile branch of archaeal phylogenetic tree than to sulphur metabolizing Thermophiles. Thermoplasma grow in nature in coal refuse piles, and Solfatanas i.e., the hot sulphur rich environments, volcanic areas or vents which yield sulphur vapours and steam.
Survival time of this cell wall less archaea has been estimated to be 15 years. Thermoplasma acidophilus is heterotrophic thermoacidophile found in acidic environments created by chemolithotrophic sulphur oxidisers but does not produce acid itself.
Q.5. Describe acetogenesis.
Ans. Some facultatively chemoautotrophic anaerobes are able to reduce carbon dioxide with H2 to acetate in place of methane, Clostridium thermoaceticum and Acetobactenum woodii, the reaction for which can be represented as:
2CO2 + 4H2 → CH3COOH + 2H2O (ΔG’O = – 25.6 kcal/mol = – 107.5 kJ/mol) … (ii)
In the acetogenesis shown in the above equation numbered (ii) the energy yield of the reaction is less favorable than the methanogenesis. Besides acetogenesis from carbon dioxide and hydrogen these organisms can also ferment CO formate and methanol to acetate and have many metabolic features in common with methanogenic bacteria.
Q.6. What is a psychrophile?
Ans. An organism which grows optimally at or below 15°C, has an upper limit for growth at about 20°c and which has lower limit for growth of 0°C or below. This definition appear in Bacteriological Reviews (1975), 39:144 – 167; and currently is most widely accepted definition, however, some authors still use the term very loosely to include psychrotrophs which is believed to be a misnomer. Psychrophilic organism include certain algae and fungi, a number of Gram negative bacteria e,g. some species of Pseudomonas and Vibrio, and a few Gram positive bacteria Clostridium spp.
The term psychrotroph has been used for the organism which can grow at low temperature e.g. 0 – 5°C) but which has an optimum growth temperature > 15°C and an upper limit of growth > 20°C. Psychrotrophs include certain algae and fungi and various gram negative and Gram positive bacteria.
Q.7. What is an acidophile?
Ans. An organism that grows optimally under acidic condition having an optimum growth pH below 6 and sometimes as low as 1 or below and which typically grows poorly or not at all at or above pH 7 e.g. Sulpholobus, Thermoplasma and Thibacillus.
Q.8. Can microorganisms tolerate extreme pH? Justify your statement.
Ans. The microorganisms generally cannot tolerate extreme pH values. Under highly alkaline or acids conditions some microbial cell components may be hydrolyzed or their enzymes may get denatured. There are, however, some acidophilic folerate or need extreme pH conditions for growth. Many fungi are acidotolerant but most bacterid are not. Some acidotolerant bacteria like Thiobacillus and acidosis like Thiobacillus and Sulfolobus create their own low pH environment by producing acids.
Lactobacillus is a mixed acid fermenter and Sulfolobus produces sulphuric acid Bacillus SSUs and acidophilus are environments created by chemolithotrophic sulphur oxidisers but do not produce acids themselves. Thermoplasma is an archeon without cell wall and live in hot acid coal refuse piles. Bacillus acidocaldarius is the native of acid hot spring.
Applications of Acidophiles:
Q.9. Give the practical importance of acidophiles that can be of applied value.
Ans. (i) Lactobacillus is used to prepare silage (stored cured fodder) and fermented foods.
(ii) Thiobacillus and Sulfolobus are employed in bioleaching of low-grade copper and uranium ores.
Q.10. What are alkaliphiles?
Ans. Many bacteria and fungi are known to bear alkaline pH upto 9 but prefer pH optimum near neutrality. The examples of true alkaliphiles are Bacillus strains like Bacillus alcalophilus and B pasteuri. Some cyanobacteria like Microcystis aeruginosa, Plectnonema nostocorum and some species of Spirulina are also alkalophilic. Halobacterium, Natronobacterium and Natronococcus are the category of alkalophiles found in saline lakes with high pH.
Q.11. Give the application of alkaliphiles.
Ans. Some alkaliphiles like Bacillus strains produce enzymes proteases and lipases which are stable at high temperature at alkaline pH in the presence of detergent. Therefore, these are used in some laundry detergents to clean fat and proteinaceous stains. It is interesting to note that Clostridium paradoxum can withstand pH greater than at 55°C and its optimal generation (doubling) time is 13 minutes at pH 9.3.
Q.12. What are thermopiles?
Ans. The thermopiles like optimum growth temperature above 40°C. Bacterium Bacillus stearothermophilus grow at comparatively high temperature (55°C to 70°C). The maximum growth temperature for most thermopile bacteria is about 99°C and many thermopile bacteria have temperature ranging from 55° to 60°C.
Q.13. What is the optimal temperature for extreme thermopiles?
Ans. The optimal temperature of extreme thermopiles is above 80°C. They grow in nature in hot-springs and effluents from Laundromats. Many extreme thermopiles, however, can remain live at freezing temperature and have been reported to have survived in antarctic frozen soil.
Q.14. How do thermopiles maintain their semipermeable properties at high temperature?
Ans. They have comparatively high molecular weight and branched fatty acids in their membranes which permit them to maintain their semipermeable properties at high temperatures.
Q.15. Name some unique habitats of thermopiles.
Ans. They grow in areas of volcanic activity; steam vents in such areas may have a temperature of 500°C. They also grow in hot springs, like Yellow stone National Park, and in other parts of the world.
Q.16. Write on Thermal vent communities and colonies of hyper thermophiles.
Ans. The thermal vent communities occur at depth of 800 to 1000 m where sea floor permits seawater to percolate deeply inside the crust and to react with the hot core material. The vent community of bacteria likes Thermotoga, Begiatoa, Thiomicrospira and additional sulphide or sulphur oxidisers of various types. The archaeobacteria that may be growing are Thermococcus litoralis, Archaeoglobus pyrodictium and Pyrobaculum, (Fig. 6.5.).
Q.17. What are barophiles?
Ans. The organisms which grow best or only under conditions of high pressure in the depth of oceans are called barophiles.
Q.18. What are barotolerants?
Ans. The organisms which can grow under conditions of high pressure but do not show preference for growth under conditions of high pressure.
Q.19. Give the range of conditions that permitted growth of barophiles.
Ans. The barophiles have been isolated from the extreme depth of 10,500 m. Some of the deep isolates were also psychrophilic and their optimum temperature and pressure influenced each other in a complex manner. An isolate from 3600 m deep waters was clearly barophilic at the in situ temperature of 4°C recorded for that bacterium.
Q.20. What is the significance of slow growing barophilic marine bacteria?
Ans. They make significant contributions to biodegradation and marine food web.
Q.21. Can barophilic bacteria be cultured?
Ans. Yayanos and his coworkers succeeded in isolating deep sea Spirillum and grew that 15 times faster at pressure between 300 and 600 atmospheric pressure than at 1 atmospheric pressure. :
Q.22. What are osmophiles?
Ans. The microorganisms which can tolerate or prefer high concentrations of organic solutes as sugars are called osmotolerant or osmophiles. Some of the noted habitats of osmophilic microorganisms are honey, sap flows, nectar of flowers, molasses and sugary syrups. Some yeasts like Debaromyces hansenii and Zygosaccharomyces rouxii are good examples of osmophiles. The moulds Aspergillus and Penicillium also are osmotolerant.
Q.23. What are halophiles?
Ans. Microorganisms which can tolerate or need high concentration of salt are called halophiles or halotolerants.
Q.24. What is “S” organisms?
Ans. It is the organism syntrophic with methanogens. Methanobacterium bryantii (formerly known as M. omelianskii) was kept in culture collection for 26 years after its original description is 1941 before it was revealed to be syntrophic association of the methanogen proper and fermentative “S” organism. The “S” organism and syntrophic fermenters of similar type were later classified and named Syntrophomonas and Syntrophobacter Both these genera are hydrogen process and need the presence of methanogens as hydrogen removers called mutualism based hydrogen transfer (Fig. 6.8)
Q.25. Give the outlines of fermentation occurring within the rumen.
Ans. The overall fermentation taking place is the rumen may be described by equation.
57.5 (C6H12O6) → 65 acetate + 20 propionate + 15 butyrate + 60 CO2 + 35 CH4 + 25H2O
Microorganisms present in the rumen convert cellulose, starch and other ingested nutrients to carbon dioxide, hydrogen gas, methane and low molecular weight organic acids as acetic, propionic and butyric acids. The organic acids are absorbed in the blood stream of the animal and on aerobic oxidation give out energy. Ruminants are capable to use proteins manufactured by microbial population. The CO2 and CH4 produced by methanogenic bacteria inside the rumen, are released outside and do not bear any nutritional benefit (Fig. 6.9).
Q.26. What are the arsenic loving extremophiles discovered recently?
Ans. According to NASA scientist as reported in the journal Science, the first organism able to ‘ substitute one of the six chemical elements crucial to life has been found, which bacterium is found in a California Mona lake (USA) that uses arsenic, a poisonous element, in place of phosphorus.
It is fascinating that bacterium breaks the golden rule of biochemistry. So far the idea has been that life on earth is composed of at least six elements: carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus. But this bacterium is an exception to this rule and has broken the fundamental tenet of the biochemistry.
