Prokaryotes - Kingdoms of Bacteria and Archaebacteria PDF

Chapter 2: Prokaryotes - Kingdoms of Bacteria and Archaebacteria 1. General characteristics Bacteria are prokaryotic & unicellular microorganisms. Simplest and most abundant on the earth's surface: High metabolic diversity + their rapid division. The vast majority of Bacteria are...

Chapter 2: Prokaryotes - Kingdoms of Bacteria and Archaebacteria 1. General characteristics Bacteria are prokaryotic & unicellular microorganisms. Simplest and most abundant on the earth's surface: High metabolic diversity + their rapid division. The vast majority of Bacteria are essential to life on earth. ✓ Source Of significant economic products: vitamins and antibiotics ✓ Decomposition and recycling; soil organic matter. Other prokaryotes cause human plant and animal diseases. 2. Structure and characteristics of prokaryotes 2.1. Morphology Different sizes and shapes. Most bacteria range from 0.2-2.0µm in diameter and from 2-8µm in length. Exists as: Single-celled forms (+++), Colonies, Filaments of joined cells. bacteria have three main shapes: - Spherical coccus, - Rod-shaped bacillus, - Spiral. Cocci: usually round but can be oval, elongated, or flattened on one side. ▪ When cocci divide, can remain attached: Diplococci ▪ Streptococci.  Most bacilli appear as single rods. ▪ Diplobacilli ▪ Streptobacilli Spiral bacteria: one or more twists; never straight.: Vibrios: curved rods Spirilla: helical shape - corkscrew Spirochetes: helical and flexible  2.1. Cytoplasm Prokaryotic: no nuclei, no mitochondria, no chloroplasts, no endoplasmic reticulum, no Golgi complex and no lysosomes. A plasma membrane - cytoplasm + ribosomes + enzymes (needed for metabolic activities). Certain bacteria have gas vacuoles to float at different depth. Prokaryotes: no true nucleus - nuclear membrane. DNA: single circular chromosome - double strand associated with different proteins. Location: central region – nucleoid. One or more plasmids - small extrachromosomal DNA molecules – independent self replication. Plasmids: often bear genes that confer resistance to antibiotics.  2.3. Cell membrane Cell membrane: selective permeable membrane - selective passage of molecules (nutrients, wastes, ions, etc.). In photosynthetic bacteria: membrane invaginations form thylakoids – photosynthesis. Cell wall: protection, stiffness and resistance to osmotic pressures. Cell wall differs between Bacteria and Archaebacteria.  2.5. Flagella Most bacteria have flagella - motility +++ Flagella rotation →→ cell movement in the medium ± ± ± Sliding by secreting sticky substances. Flagella may be involved in virulence.  2.6. Pili and fimbriae Fimbriae and pili are filamentous structures. Fimbriae - attachment: organism – food source – surfaces. Pili: Some are involved in: ▪ Conjugation: connect the two cells – retraction – drawing the 2 cells together - transfer of DNA. ▪ Pathogenicity for plants and animals. ▪ Serving as receptors for specific bacteriophages. Conjugating Escherichia coli cells The elongated donor cell at the right in this electron micrograph is connected to the more rotund recipient cell by a long pilus, which is the first step in conjugation. Numerous short fimbriae are visible on the donor cell. 2. 7. Chemotaxis and Phototaxis Many bacteria are capable of oriented movements (taxis) in response to: o Chemical stimuli (chemotaxis) o Light stimuli (phototaxis)  2.8. Metabolic diversity Bacteria: very high metabolic diversity 2 elements organic compounds synthesis: energy and carbon. According to their energy source: - Phototrophs: : use light as energy source Convert light energy into chemical energy: photosynthesis. - Chemotrophs: use inorganic or organic chemicals as an energy source. According to their carbon source: - Autotrophs: use CO2 - Heterotrophs: need organic compounds (glucose) case of the majority of prokaryotes. The terms used to indicate the energy and the carbon source of Prokaryotes can be used in combination showing the metabolic diversity of those organisms Carbon source Heterotrophs Autotrophs Energy source (use organic compounds (use CO2 as a carbon other than CO2 as a source) carbon source) Phototrophs (use light as an energy Photoautotrophs Photoheterotrophs source) Chemotrophs (use organic or Chemoautotrophs Chemoheterotrophs inorganic chemicals as an energy source) Heterotrophs are: Saprophytes (vast majority) Parasitic Symbiotic 2.8.1. Saprophytes Get carbon from partially degraded or dead organic matter in aerobic or anaerobic conditions. Saprophytes are: o Decomposers o Recyclers of organic matter → → → return to the inorganic state (C, N, S, P) 2..8.2.. Symbiotic Symbiotic association: Mutual benefit between two living organisms. Rhizobium: roots of legumes - fix of atmospheric nitrogen (N2) used by the plant.  2.8.3. Parasitic ▪ Use organic matter in living animals or plants ▪ Origin of many diseases: pathogenic.  2.9. Effects of the external factors Oxygen has an effect on growth: ✓ Strict aerobics: require oxygen for respiration. ✓ Strict anaerobics: cannot live in the presence of oxygen. ✓ Facultative anaerobics: live in the presence or absence of oxygen.  ability of Prokatyotes to grow optimally in relation to temperature: Psychrophilic:: grow at low temperatures. Mesophilic: develop at moderate temperatures. Moderate thermophiles: grow at high temperatures. Hyperthermophilic: grow at very high temperatures. 3. Kingdom of Eubacteria or Bacteria Eubacteria = or true bacteria: diverse group. Are classified according to: ► - Their staining properties, ► - Type of metabolism, ► - Shape, ► - Cell wall structure, ► - Locomotion (motility) type 3.1. Cell wall Cell wall → + peptidoglycan Cell wall structure: 2 categories - using the Gram stain: o Gram + o Gram - Gram-positive bacteria: + Single thick layer of peptidoglycan Gram-negative bacteria: 2 layers: thin inner layer of peptidoglycan + an outer membrane 3.2. Endospores o Formed within the cell wall of a parent cell o in Gram+ bacteria Spore will remain dormant → induced to germinate > hydrating (revive the vegetative state)  Bacteria survive by producing endospores. Remain viable = multiply over centuries. → dormant under conditions inadequate to growth. Resist desiccation Not killed by long exposures to temperatures as high as 80˚C, Not killed in boiling water for up to 20 minutes  3.3. Cyanobacteria Bluish green, sometimes purplish photosynthetic bacteria Chlorophyll "a", Carotenoids (red or yellow) and other accessory pigments, Phycobilins (red or blue photosynthetic pigments). Color of cyanobacteria → phycobilins: - Capturing light energy - Mask chlorophyll 2 types of phycobilins: - Phycocyanin: blue pigment - Phycoerythrin: red pigment  Plasma membrane → intracellular invaginations, (concentric & d parallel) thylakoids. Phycobilins → outer side of the thylakoids Main sugar reserve = glycogen. ▪ Lack flagella ▪ Mobile species move by sliding. Are all Gram - bacteria. Cyanobacteria: ✓ Lives as unicellular or ✓ lives in colonies or ✓ form multicellular filaments. Many filamentous cyanobacteria are capable of fixing atmospheric nitrogen (N2) → specialized cells, heterocysts. `In addition to heterocysts, some cyanobacteria form resistant cells = akinetes > with thick walls and resistant to drought. They are found on the bottom of the deep waters and moist soils. Some may develop on the water surface: they are planktonic species (free-swimming forms or driven by currents).  3.4. Mycoplasma Mycoplasmas are a particular group of bacteria lacking cell walls. Have many form: from small stick to branched filament. They are all parasites causing lung diseases for animals and plants. 4. The Archaea Archaea: primitive prokaryotes. Biochemically - different from other prokaryotes. o Absence of peptidoglycan in their cell walls. o Unusual lipids in their plasma membranes, o Distinctive RNA molecules; RNA polymerase is more like that of eukaryotes than that of Eubacteria. Archaebacteria inhabit extreme environments: hot springs whose temperatures may exceed 100ᵒC and deep-sea Based on metabolic characteristics, 4 groups: Methanogens, Halobacteria, Extreme thermophile Thermoplasma. Archaea: Some live in soils - others in the marine environment. Archaea are not pathogens of humans.  Characteristics Bacteria Archaea Eukarya Cell type Prokaryotic Prokaryo Eukaryotic tic Nuclear envelope Absent Absent Present Number of chromosome 1 1 Many Chromosome shape Circular Circular Linear Peptidoglycan in cell wall Present Absent Absent Membrane lipids Ester Ether Ester Organelles (mitochondria and plastids) Absent Absent Present) Cytoskeleton Absent Absent Present Photosynthesis in the chloroplast Absent Absent Present Capacity to grow > 100˚C No +/- Yes No Ester Ether  4.1. Methanogens Produce methane (CH4) from hydrogen (H2) and carbon dioxide (CO2). ✓ Strict anaerobics. ✓ Chemotrophs. ✓ Carbon source: - CO2 > autotrophy - Small organic molecules > heterotrophy. All methanogens use ammonium (NH4+) as a nitrogen source. Some can fix nitrogen. Used as decomposers for biological treatment of wastewater. The largest reserves of natural gas used as fuel nowadays were produced from a historical methanogenic prokaryotes activity. Methanogens are also found in the cattle and other ruminant’s intestine, where they play an important role in the cellulose digestion.  4.2. Extreme halophiles (Halobacteria) Halobacteria live in areas where the salt concentration is very high. Great Salt Lake in the United States, the Dead Sea or in the sea water pools for the production of kitchen salt (sodium chloride, NaCl). Most extreme halophiles require a salt concentration of 12- 23% for an optimal growth. Their cell walls, ribosomes and enzymes are stabilized by sodium ion (Na+). Necessary amount of oxygen is limited by the high salt concentration, most species need oxygen. Extreme halophiles can be chemoheterotrophs, they find their energy from the oxidation of organic compounds. For some, light is involved in the synthesis of ATP without the intervention of chlorophyll pigment. ATP production is due to a protein, bacteriorhodopsin present in the plasma membrane. Bacteriorhodopsin also gives pink color to halophilic colonies forming masses in seawater.  4.3. Extreme thermophiles or thermoacidophiles Live in areas both hot and acidic. Growth is optimal at a temperature not lower than 80 ºC and a pH between 2 and 4. Some grow at more than 110ºC. They are strict anaerobes. These archaea are found in hot places rich in sulfur. They also thrive in hydrothermal fissures on the ocean floor.  4.4. Thermoplasma Represented by only one species T. acidophilum belonging to the genus Thermoplasma. They lack cell wall (as mycoplasma). Have a small size and can be spherical or filamentary. They live in places where temperatures range from 32 to 80 ºC. Aerobic and anaerobic metabolism.