#Infodump 4
#Infodump 4
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An overview of the major groups of microorganisms
An overview of the major groups of microorganisms
Bacteria
relatively simple, unicellular microorganisms which thrive in diverse environments.
Genetic material: They are prokaryotes as their genetic material is not enclosed within a nuclear membrane nor do they possess membrane bound organelles. The DNA swims freely either in the form of a twisted, thread-like mass known as nucleoid or as circular pieces called plasmid.
Shape and arrangement: Bacteria can appear in one of the several shapes of which five are basic shapes:
Spherical (cocci)
Rod (bacilli)
Spiral (spirilla)
Comma (vibrios)
Corkscrew (spirochetes)
Though there can be various other shapes such as star or square shaped bacteria, albeit uncommon. Individual bacteria may appear in pairs, chains, clusters, or other groupings; such arrangements are usually characteristic of a specific genus or species of bacteria.
Figure: Different shapes of bacteria
Structure: Bacteria are generally encased by two protective layers: an outer cell wall and an inner cell membrane. The cell walls are largely composed of a carbohydrate and protein complex called peptidoglycan. Exception to this is mycoplasma, which do not possess a cell wall at all as well as certain bacteria which may have a third, outermost protective layer called the capsule. To aid in mobility and attachment to host bacteria have whip-like extensions covering its surface – longer ones called flagella or shorter ones called pili.
Reproduction: They generally reproduce by binary fission, which is a process of asexual reproduction. In this method the ‘parent’ bacterial cell makes a copy of its DNA within the cell which separates into alternate ends of the cell. The cell then grows twice its size by doubling its cellular content. The plasma membrane (cell membrane) pinches the cells apart pushing the duplicated content out creating two identical ‘daughter’ cells.
Some bacteria also reproduce by budding (example: cyanobacteria, planctomycetes, firmicutes). Budding is also a type of asexual reproduction where bud or a small outgrowth is produced from the parent cell which when completely matured, detaches from the parent cell.
These two methods produce offspring which are the exact replica of the parent cell. There is another method via which bacterial cells induce variation in their genetic material, it is called horizontal gene transfer, a method which involves integration of additional DNA, often acquired from the surrounding, in order to adapt and survive in a new environment. There are three mechanisms of horizontal gene transfer: transformation, transduction, conjugation.
Archaea
(“Ancient things” in Greek)
They have several features in common with eukaryotes and others with bacteria and still other traits that are exclusively archaea.
Example: Their informational genes – genes which code for protein involved in replication, transcription and translation – are similar to those of eukaryotes whereas genes involved in metabolism are similar to bacterial genes. They are prokaryotic cells like bacteria but lack peptidoglycan, though some contain a structurally similar substance called pseudopeptidoglycan or pseudomurein in their cell wall, if they have one.
Archaea are known to inhabit a wide range of habitat. Most commonly found in extreme conditions, they were considered microbes of “extreme environments” and hence titled “extremophiles”.
Some types of archaea are explained below:
Methanogens: Found to inhabit marshy lands these organisms are capable of converting carbon dioxide, methanol and formic acid into methane. They can also be located in the guts of ruminants (cows, buffaloes, etc.) to aid in digestion. They are also responsible for the production of methane (biogas) from the dung of these animals. Example: Methanobacterium, Methanococcus, Methanosarcina
Halophiles (halo = salt; philic = loving): Live in extremely saline environments such as salt lakes, sea, brines, etc. (Great Salt Lake and the Dead Sea). They are primarily chemo-organoheterotrophs. Most species require sodium chloride (NaCl) concentration ≥ 1.5M but some have the ability to survive in as little as 0.5M. Example: Halobacterium, Halococcus, Natronobacterium.
Thermoacidophiles: capable of tolerating high temperature as well as high acidity. Often found in hot springs in temperatures as high as 800C and pH as low as 2, (hot springs at Yellowstone National Park). Under aerobic conditions they oxidise sulphur to sulphuric acid and the energy obtained from this reaction is utilised for the synthesis of organic food. Therefore they are chemosynthetic in nature (obtain energy by oxidation of inorganic substances). This converts the medium they are growing in highly acidic due to the production of sulphuric acid. Under anaerobic conditions sulphur is reduced to hydrogen sulphide (H2S). Example: Desulfurococcus, Pyrodictium, Pyrococcus, Sulpholobus.
Archaeal genome due to its complexities and size make it quite difficult for the taxonomist to classify. According to most taxonomists, within Archaea, for now, there are 5 major phyla: Crenarchaeota, Euryarchaeota, Korarchaeota, Nanoarchaeota, and Thaumarchaeota. Though it is likely that there are several other Archaeal groups which have not been studied or classified.
Fungi (Eumycota):
(fungus: mushroom in Latin)
(eu: true; mykes: fungus in Greek)
They are eukaryotic organisms that are spore bearing, achlorophyllous, heterotrophic have absorptive nutrition and can reproduce both sexually and asexually. Organisms in Kingdom Fungi can be unicellular (yeast) or multicellular (mushroom). Fungus are saprophytes, which means that they acquire their nutrients from dead organic material by releasing degradative enzymes into the environment. This enables their absorption of the soluble products-a process sometimes called osmotrophy.
They are also important decomposers as they are responsible for degrading complex organic material to simple organic compounds and inorganic molecules present in the environment thus making carbon, phosphorous, nitrogen and other important constituents available for living organisms.
Structure: Haploid body and thalloid, i.e., it is not differentiated into root, stem and leaves. The body is made up of long filaments, called hyphae that criss-cross to form a network known as mycelium. The cell wall of the hyphae is made up of chitin. Which is a polysaccharide consisting of nitrogenous compounds and is basically made up of acetylglucosamine. In some fungi the cell wall is made up of cellulose.
Reproduction: The reproduction in fungi can be sexually or asexually.
Asexually they can reproduce by – fission (mitosis of parent cell into two daughter cells by a simple constriction and formation of new cell wall); fragmentation (breaking of mycelium into 2 or more fragments due to mechanical injury, decay or other reasons and the individual fragments grow into independent mycelium); budding (forming buds on surface of parent cell which cut off to form new individuals). They can also reproduce through asexual spores, single celled specialised structures which detaches from the organism, disperses and germinates after landing on suitable substrate. There are different types of spores: Sporangiospore, Arthoconidia, Conidiospore, Blastospore, Chlamydospore.
Sexual reproduction occurs through oospores, ascospores and basidiospores. The sexual cycle involves three steps: plasmogamy > karyogamy > meiosis.
Examples of some fungi: Aspergillus, Penicillium, Tuber aestivum (truffles), Saccharomyces cerevisiae (yeast)
To learn about the remaining types of microorganisms don't miss our next infodump!!
References:
Gerard J. Tortora, Berdell R. Funke, Christine L. Case (2013), Microbiology: An Introduction (Eleventh edition), Pearson.
Michael J. Pelczar, JR., E.C.S. Chan, Noel R. Krieg (2001), Microbiology (Fifth Edition), McGraw Hill Education.
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