TAXONOMY and NOMENCLATURE

• Bacterial cells exhibit all characteristics of life, although they do not have the complex system of membranes and organelles found in more advanced single-celled organisms.
• These less complex cells, which include Bacteria and Archaea, are called prokaryotic cells or prokaryotes.
• The more complex cells, containing a true nucleus and many membrane-bound organelles, are called eukaryotic cells or eucaryotes.
• Eucaryotes include such organisms as algae, protozoa, fungi, plants, animals and humans.
• Some microorganisms are prokaryotic, some are eukaryotic, and some are not cells at all.
• Acellular Microbes are small, obligate, intracellular particles that possess no organelles, no cytoplasm, and no cell nucleus or nucleoid.
• Instead, Acellular Microbes are comprised of two basic components: a nucleic acid genome (DNA or RNA) and a surrounding coat of protein (capsid).
• Viroids are tiny fragments of nucleic acid known to cause diseases in crop plants.
• Viroid RNA encodes no proteins, leading to the hypothesis that the viroid RNA interacts with host cell RNA, inactivating proteins that bring about disease through loss of cell function.
• Another hypothesis suggests the viroid RNA “silences” host cell “target RNA,” again bringing about disease through loss of cell regulation.
• Disease causation remains to be determined but so far viroids have been identified as pathogens of plants only.
• Prions are microorganisms that cause diseases such as Transmissible Spongiform Encephalopathies (TSEs; mad cow disease in cattle, scrapie in sheep and goats, chronic wasting disease in elk and deer and Creutzfeldt-Jacob Disease in humans).
• Stanley Prusiner and colleagues isolated an unusual protein from scrapie-infected tissue, which they thought represented the infectious agent.
• The proteinaceous infectious particle, or prion, was identified as a protein and does not contain nucleic acid.
• The protein-only hypothesis predicts that prions are composed solely of protein and contain no nucleic acid.
• Scientific names are Latinized because Latin was the language traditionally used by scholars.
• Scientific nomenclature assigns each organism two names: the genus (plural: genera) is the first name and is always capitalized; the specific epithet (species name) follows.
• Scientific names can describe an organism, honor a researcher, or identify the habitat of the species.
• Following are some examples of microbial names: Klebsiella pneumonia honors bacteriologist Edwin Klebs; Salmonella typhimurium honors public health microbiologist Daniel Salmon; Streptococcus pyogenes refers to the appearance of cells in chains; Saccharomyces cerevisiae is a fungus that uses sugar; Penicillium notatum has a tuftlike or paintbrush appearance microscopically and its spores can easily spread in air.
• Before the existence of microbes was known, all organisms were grouped into either the animal kingdom or the plant kingdom.
• When microscopic organisms with characteristics of animals or plants were discovered late in the seventeenth century, a new system of classification was needed.
• Still biologists could not agree on the criteria for classifying new organisms they were seeing until the late 1960s.
• The Five Kingdom Classification by Whittaker includes Monera (Kingdom Prokaryotae), Fungi, Plantae, Protista, and Animalia.
• The Four Divisions of Bacteria under Kingdom Monera are Division Gracilicutes (gram negative), Division Firmicutes (gram positive), Division Tenericutes (without cell wall), and Division Mendosicutes (archaebacteria).
• In 1978, Carl Woese devised a system of classification based on cellular organization of organisms.
• The Three Domain Classification by Carl Woese includes Bacteria, Archaea, and Eucarya.
• The taxonomic classification of humans, brewer’s yeast, and a common bacterium is as follows: Human Being, Brewer’s Yeast, Escherichia coli.
• There are two types of prion proteins: Normal cellular prions (PrP C) found on surfaces of brain cells and abnormal prions (PrP SC) with different shape found in scrapie.
• Transmissible Spongiform Encephalopathies are spread by the infectious PrP SC binding to normal PrP C, causing the latter to change shape.
• In a domino-like scenario, the newly converted PrP SC proteins, in turn, would cause more PrP C to become abnormal.
• The PrP SC proteins then form insoluble aggregates, which are responsible for the large, sponge-like holes left where group of nerve cells have died.
• PrP SC does not trigger an immune response.
• Many archaea are extremophiles, meaning that they live in extreme environments.
• Extremophiles are categorized based on the type of extreme environment they inhabit, such as Acidophiles for extremely acidic environments, Alkalophiles for extremely alkaline environments, Thermophiles for extremely hot environments, Psychrophiles for extremely cold environments, Halophiles for extremely salty environments, and Piezophiles (formerly barophiles) for extremely high pressure environments.
• The phyla under Domain Archaea include Euryarchaeota, Crenarchaeota, and Korarchaeota.
• Euryarchaeota contain organisms with varying physiologies, including groups such as the methanogens that are killed by oxygen gas and are found in environments devoid of oxygen gas.
• Crenarchaeota tend to grow in hot, acidic environments, thriving in hot sulfur springs and volcanic vents.
• Korarchaeota (tentative phylum) consists of hyperthermophiles.
• Nanonarchaeota (tentative phylum) consists of hyperthermophiles.
• The Bacteria have adapted to the diverse environments on Earth, inhabiting the air, soil and water, and they exist in enormous numbers on the surfaces of virtually all plants and animals.