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Everything you need to know about microbial diversity. Some of the frequently asked questions are as follows:-
Q.1. What is microbial diversity?
Ans. The microbial diversity is the diversification (variations) among microorganisms both non-cellular and cellular, and prokaryotic and eukaryotic on the basis of their structure and function.
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Q.2. What is microbial mat?
Ans. It is a complex benthic microbial community that forms a cohesive layer and is typically dominated by cyanobacteria or other photosynthetic prokaryotes and occasionally micro-algae. Microbial mats are found in the regions where the environmental stress tends to exclude or reduce the number of metazoans, e.g., in intertidal and hyper saline regions, in hot springs and around hydrothermal vents. The microorganisms occurring in microbial mats include the species of Lyngbya and Macro coleus, various purple photosynthetic bacteria Chloroflexus and certain aerobic and anaerobic chemotrophs as sulphur reducing bacteria.
Q.3. Name the place from which Precambrian fossilized photosynthetic bacteria have been collected from fig tree formations, the fossilized stromatolite being 3.5 billion years old.
Ans. Western Australia.
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Q.4. Which is older, the evolution of microorganisms or plants and animals?
Ans. Microorganisms have been evolving for over 3.8 billion years as compared to 0.6 billion years in the case of plants and animals.
Q.5. How did the evolution of new species of microorganisms come about?
Ans. The microorganisms evolved through interactions of their genomes with the environments.
Q.6. What is a unit of biological or microbial diversity?
Ans. A species is a unit of biological diversity.
Q.7. What is the effect of evolution on microbial diversity?
Ans. The evolution leads to formation of new kind of microorganisms. Thereby the number of new types of organisms increase. In other words the microbial diversity increases.
Q.8. What is a microbial species or the concept of microbial species?
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Ans. A microbial species may be regarded as a group of individual populations or strains that show a high level of similarity and differ from populations or strains in related groups. In case of bacterial species the members of the same species possess DNA homology values above 70 per cent.
Also the bacterial species have a limited range of mole per cent G + C as the DNA molecules with significant differences in mole per cent G + C do not show a high level of homology. The species is a taxonomic category ranking just below a genus. The individuals of a species exhibit a high degree of mutual similarity. In the higher organisms which reproduce by sexual reproduction, the members of a species can inbreed actually or potentially.
Q.9. Which things lead to proliferation of some kinds of organisms and extinction of others?
Ans. Genetic variations and natural selection.
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Q.10. What is the phylogeny of microorganisms?
Ans. The evolutionary history of microorganisms is their phylogeny.
Q.11. What might have comprised the cytoplasmic membranes of progenitor cells?
Ans. Perhaps a mixture of glycerol ester-linked phospholipids and glycerol ethers comprised the cytoplasmic membrane of progenitor cells.
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Q.12. Give an example of the bacterium which may be a descendant of deep rooted divergence and has retained the mixture of ether and ester glycerol based lipids in its cytoplasmic membrane.
Ans. Aquifex. The Aquifex pyrophilus can grow up to 95°C, however, the optimum temperature is 85°C, is an extreme thermopile.
Q.13. Which features of cytoplasmic membranes lead to adaptation of extremely thermophilic archaea to survive at high temperatures?
Ans. They possess cytoplasmic membranes with glycerol diethers or diglycerol tetraethers that make them adaptive for survival at high temperatures.
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Q.14. How are eukaryotic organisms chimeric?
Ans. It is believed that some of the organelles of the eukaryotes are derived as a result of unions of distantly evolved microorganisms, the mitochondria, chloroplasts and perhaps some other organelles might have been acquired as a result of endosymbiosis.
Q.15. How could it be concluded that mitochondria originated from proto-bacteria or purple bacteria and chloroplasts from cyanobacteria?
Ans. Analysis of cytochromes, ferredoxins and rRNA molecules of the organelles revealed the origins.
Q.16. What is a molecular chronometer?
Ans. A measure of evolutionary time is called molecular chronometer.
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Q.17. What is evolutionary distance?
Ans. Evolutionary distance is a measure of relative similarity of two microorganisms (or organisms) on the basis of similarity of nucleic acids and proteins.
Q.18. How do Aquifex species differ from other bacteria?
Ans. The species of Aquifex have glycerol diethers instead of phospholipids which are found in other bacteria.
Q.19. Why are the bacteria of Aquifex the first bacterial genus to be named so?
Ans. Aquifex means water making, they use H2, S2O32– (thiosulphate) and S° (sulphur) as electron donors to reduce oxygen to water and thereby are known as water makers.
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Q.20. Which are the first bacterial genera to evolve?
Ans. They are Aquifex and Hydrogenobacter.
Q.21. Name an extreme thermophile that was isolated from a hydrothermal vent.
Ans. Aquifex pyrophilus.
Q.22. What is the range of temperature required by Aquifex pyrophilus for growth?
Ans. The optimum temperature for Aquifex pyrophilus is 85°C but it can grow at temperature as high as 95°C.
Q.23. Give some unique characteristics of the genus Hydrogenobacter of Aquificales.
Ans. (1) They are obligate autotrophs, and represent unusual lipid profile with linear C 18: 0 and C 20: 1 as major lipids.
(2) They possess a unique quinone, 2 methylthio -1, 4 naphthoquinone.
(3) They have a unique carotenoid pigment.
(4) They possess outer protein coats.
(5) They have a relatively small genome size (Ca 1.0 × 106 bp) compared with the genomes of other bacteria (Ca. 4.0 × 106 bp).
Q.24. What could have been the ancestral bacterial progenitor?
Ans. Perhaps some thermophilic individual which might have fixed carbon chemoautotrophically could have been the bacterial progenitor.
Q.25. What are thermotogales? Give their common characteristics.
Ans. It is a group of extremely thermophilic microorganisms which are, phylogenetically distant from bacteria.
Their important characteristics are:
(1) They are Gram-negative, non-spore forming rod-shaped cells.
(2) They are thermophilic.
(3) They are anaerobic.
(4) They possess fermentative metabolism.
(5) They usually possess an outer sheath-like envelope called “toga” that balloons over the ends of the cell.
(6) They lack meso-diaminopimelic acid in their peptidoglycan.
(7) They are sensitive to lysozyme.
(8) They have unusually long chains of dicarboxylic fatty acids in their lipids.
Q.26. Why are the Thermotogales placed under the bacterial domain?
Ans. On the basis of comparison of bacterial DNA sequences of translation elongation factor Tu (EF— Tu), and the presence of classical Embden-Meyerhof pathway of glycolysis in the Thermotogales which is a feature of bacteria and is lacked by archaea.
Q.27. Name two radiation resistant bacteria.
Ans. Deinococcus and Deinobacter of the group Deinococci are highly radiation resistant bacteria. These have, therefore, been used to assess the effectiveness of radiation sterilization. This is because they have effective repair mechanism for damaged DNA. They also have a high concentration of carotenoids which absorb radiation. The carotenoids are found in all radiation resistant bacteria.
Q.28. What are proteobacteria? Give their main subgroups.
Ans. They are purple bacteria. The proteobacteria have been divided into five separate lineages based on ribosomal RNA sequencing which are: alpha, beta, gamma, delta and epsilon.
Q.29. Which are two major evolutionary lines of descent?
Ans. These are:
(1) Gram positive bacteria with a low mole per cent G + C (clostrial lineage) and
(2) Gram positive bacteria with high mole per cent G + C which is the actinomycetes lineage.
Q.30. Which pigments are found in Cyanobacteria?
Ans. The pigments found in Cyanobacteria are:
(1) Chlorophyll-a and
(2) Phycobiliproteins.
Q.31. What is common between chlamydias and planktomycetes?
Ans. Both of them lack peptidoglycan in their cell walls.
Q.32. What are the differences between Chlamydia and planktomyces?
Ans. The Chlamydia is exclusively intracellular in animal cells while planktomycetes are free living.
Q.33. Which are the three Kingdoms (branches) of Archaea?
Ans. They are Kingdom Crenarchaeota, Kingdom Euryarchaeota and Kingdom Korarchaeota.
Q.34. Give outstanding variations found in bacteria.
Ans. Bacteria have variable size and shape and their morphological shape varies from typical rods and cocci, grotesque forms to prosthecate bacteria. They may reproduce by binary fission, budding and forming multicellular filamentous aggregates.
Metabolically they may be chemoautotrophic depending on enormous array of organic matter or even phototrophic oxygen producing. They show an oxygenic photosynthesis to chemolithotrophy as a result of oxidation of various inorganic substances.
The bacteria on the basis of their metabolism can transform almost all naturally occurring substances but they cannot break many of the man-made substances creating pollution. They occur in a wide range of habitats, e.g., from cold and dark depths of oceans to hot thermal springs, on and in roots and leaves of plants to the surface of the body of most animals including humans.
Q.35. Which group of bacteria have been called the ‘undulopodia’ of eukaryotic cells and the precursors of sensory perception in animals?
Ans. The spirochetes.
Q.36. What are spirochetes?
Ans. The spirochetes are helically-coiled, rod-shaped Gram negative bacterial cells wound around flagella. The flagella of a spirochete cell comprise central axial filaments which are attached al the ends of the cell to flagellar motors consisting of hook, shaft and four rings. The central axial flagella are endo-flagella.
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Q.37. What are the “postage stamp-like sheets of cells” of archaea found in Red Sea?
Ans. The square cells of extremely Archaean Halo-bacterium species isolated from the Red Sea seem to be divided into two dimensions. They form floating gas vacuolated sheets of cells giving the appearance of “postage stamp-like sheets of cells”.
Q.38. What is the most striking characteristic that differentiates archaea from other bacteria and eukaryotes?
Ans. They have ‘ether’ linkages in the lipids of their cytoplasmic membrane.
Q.39. Name the only individuals capable of producing methane under anaerobic and often under thermophile conditions.
Ans. Methanogens.
Q.40. Which are the most primitive physiological and metabolic traits conserved by the archaea?
Ans. These characteristics are to survive at high temperatures and without oxygen. These are the traits that archaea might have adapted while the average temperature of the earth was much higher and there was no molecular oxygen.
Q.41. Which characteristics of the archaeal cells have enabled them to survive under most harsh conditions inhospitable to life?
Ans. These characteristics are:
(1) Ether linkages in their membrane lipids.
(2) Diverse types of non-peptidoglycan cell wall.
(3) Archaeal histone-like proteins which provide stability to archaeal chromosomes.
(4) Introns within the archaeal protein and archaeal splicing mechanism.
(5) The proteins which are relatively resistant to denaturation due to the presence of amino acid sequences and hydrophobic regions.
