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PROKARYTOTES Domain Bacteria Domain Archea EUKARYOTES Domain Eukarya Fig. 1. The three domains of life. Table 1. Major Differentiating Characteristics of Bacteria and Eukaryotic Cells Characteristic Bacteria (Prokaryotes) Eukaryotes Size (diameter) 1-5 m 10-100 m Chromosomes One (circular) Two or more Introns (non-coding parts of genes) Absent Present Nuclear membrane Absent Present Cell division By binary fission By mitosis (or meiosis) Membranous organelle Absent Present (mitochondria, ER, Golgi, lysosomes, chloroplasts, peroxisomes) Ribosome size 70 S 80 S Peptidoglycan cell walls Present Absent Sterols in membrane Absent Present Flagella Basal body/hook/filament; Microtubules (9 + 2); flagellum rotation flagellum undulation Fig. 3. The Gram Stain Colour of the cells --------------------------------------Gram +ve Gram -ve 1. Bacterial are treated with primary stain, crystal violet 2. Cells are treated with mordant stain, potassium iodide and iodine, which forms a complex with the crystal violet 3. Cells are decolourised by brief treatment with ethanol. Gram +ve cells but not Gram –ve cells retain some of the crystal violet-iodine complex due to a thicker cell wall (peptidoglycan). 4. Cells are counterstained with a red dye, carbol fuschin. Gram –ve cells stain red whereas Gram +ve cells retain their purple colour. N.B. As cultures age, Gram +ve cells often become Gram -ve due to wall deterioration. Table 2. General characteristics of selected pathogens Bacteria Shape Gram Motile Spores Staphylococcus aureus Coccus +ve No No Streptococcus pyogenes Coccus +ve No No Bacillus anthracis Rod +ve No Yes Clostridium tetani Rod +ve Yes Yes Diseases caused Superficial and invasive infections Superficial and invasive infections Anthrax Tetanus Escherichia coli Pseudomonas aeruginosa Vibrio cholera Salmonella enterica Neisseria meningitidis Bordetella pertussis Legionella pneumophila Treponema pallidum Diarrhoea; meningitis Opportunistic pathogen Cholera Gastroenteritis Meningitis Whooping cough Legionnaire’s disease (pneumonia) Syphilis Rod Rod Rod Rod Coccus Rod Rod Helical -ve -ve -ve -ve -ve -ve -ve -ve Yes Yes Yes Yes No No Yes Yes No No No No No No No No THE BACTERIAL CYTOPLASM COMPOSITION Water ( 70-80%), Nucleic acids (DNA & RNA), Proteins, Carbohydrate, Low-Mr compounds, inorganic ions. STRUCTURES PRESENT Bacterial Chromosome: single long circular double-stranded helical DNA molecule ( 4 x 106 base pairs [4 mega base pairs] in length), tightly wound as supercoils. The hereditary information defining the cell’s structures and functions. N.B. Absence of a nuclear membrane. Plasmids: Extrachromosal small circular independently replicating double-stranded DNA molecules often encoding features which enhance the survival of organisms in a particular environment e.g. virulence factors. Ribosomes: 70S in size (cf 80S in eukaryotes), composed of small 30S subunit and large 50S subunit; site of protein synthesis. Cytoplasmic Inclusion Bodies: Granules/globules usually contain storage material (energy reserve) in polymerised form e.g. starch, glycogen, polyhydroxybutyric acid, sulphur, and polyphoshate (metachromatic or volutin granules). Specialized Inclusion Bodies: Gas vesicles (buoyancy in aquatic bacteria); magetosomes (iron oxide deposits acting as bar magnets and allowing bacteria to orient and move along geomagnetic field lines.) FUNCTIONS Houses cell’s hereditary information Genome replication Synthesis of DNA and RNA Synthesis of proteins Generation of ATP by oxidation of glucose and other C-sources (glycolysis, citric acid cycle) Early stages of peptidoglycan biosynthesis (synthesis of peptidoglycan building blocks) Numerous other “housekeeping” and regulatory activities Fig. 21. Right: DNA strands released from a lysed bacterial cell. Left: Poly- -hydroxybutyrate granules in Rhodovibrio sodomensis. BACTERIAL ENDOSPORE PRINCIPAL GENERA: Bacillus (aerobe) and Clostridium (obligate anaerobe) Table 4. Major Differences between Endospores and Vegetative Cells Characteristic Structure Vegetative Cell Typical Microscopic appearance Enzyme activity, metabolism, biosynthesis mRNA Heat resistance Chemical & radiation resistance Lysozyme resistance Calcium content Dipicolinic acid content Small acid soluble spore proteins Cytoplasmic pH Nonrefractile High Present Low Low Low Low Absent Absent About pH 7 Endospore Distinct & complex; thick spore cortex, spore coat; exosporium Refractile Low or absent Low or absent High (killed at 121 oC 15 min) High High High Present Present About pH 5.5-6.0 IMPORTANT SPORE-FORMING PATHOGENS: B. anthracis (anthrax; germ warfare agent); B. thuringiensis (insect pathogen producing toxic crystals); Cl. botulinum (food poisoning botulism); Cl. tetani (tetanus); Cl. perfringens (food poisoning; gas gangrene). SPORULATION CYCLE: Sporulation – exhaustion of an essential nutrient (e.g. C or N source); spore formation Dormancy – cryptobiotic (no metabolic activity yet potential viable) for many thousands of years Activation – usually by heat or mechanical forces; presence of essential nutrients Germination – water , spore swelling; loss of cortex, DPA & resistance to heat & chemicals Outgrowth – synthesis of new RNA, DNA and protein; formation of vegetative cell