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Bacterial Cell Structure
Fig. 4.1
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Cytoplasm dense gelatinous solution of sugars, amino acids, & salts
70-80% water serves as solvent for materials used in all cell functions
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Chromosome single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid
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DNA temperature melting Bacteria classification
G + C
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plasmids small circular, double-stranded DNA
free or integrated into the chromosome duplicated and passed on to offspring not essential to bacterial growth & metabolism may encode antibiotic resistance, tolerance to toxic metals, enzymes & toxins used in genetic engineering- readily manipulated & transferred from cell to cell
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Ribosomes made of 60% ribosomal RNA & 40% protein
consist of 2 subunits: large & small procaryotic differ from eucaryotic ribosomes in size & number of proteins site of protein synthesis All cells have ribosomes.
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Inclusions, granules intracellular storage bodies
vary in size, number & content bacterial cell can use them when environmental sources are depleted Examples: glycogen, poly-b-hydroxybutyrate, gas vesicles for floating, sulfur and polyphosphate granules
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Fig 4.10
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Cytoplasmic membrane Protoplast Spheroplast L forms
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4 groups based on cell wall composition
Gram positive cells Gram negative cells Bacteria without cell walls Bacteria with chemically unique cell walls
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Gram positive Gram negative
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Gram positive Gram negative
Fig 4.16
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Lipopolysaccharide O-antigen Highly variable n Core Heptoses
Ketodeoxyoctonic acid Lipid A Glucosamine disaccharide Beta hydroxy fatty acids (Hydroxy myritic Acid)
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LPS function Endotoxins Exotoxins
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Gram positive wall
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Gram negative cell wall
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Peptidoglycan
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Cytoplasm Cytoplasm Periplasmic space Lipoteichoic acid
Peptidoglycan-teichoic acid Cytoplasmic membrane Cytoplasm Lipopolysaccharide Porin Outer Membrane lipoprotein Periplasmic space Inner (cytoplasmic) membrane Cytoplasm
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Gram Positive Cell Envelope
Lipoteichoic acid Peptidoglycan-teichoic acid r r r Cytoplasmic membrane Cytoplasm
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Glycocalyx Coating of molecules external to the cell wall, made of sugars and/or proteins 2 types capsule - highly organized, tightly attached slime layer - loosely organized and attached Functions attachment inhibits killing by white blood cells Receptor (K antigen)
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2 Types of Glycocalyx
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Biofilms
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Flagella
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lophotrichous Monotrichous amphitrichous peritrichous
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Fig 4.2b
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Fimbrae Adhesion to other cells and surfaces
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pili rigid tubular structure made of pilin protein
found only in Gram negative cells Functions joins bacterial cells for DNA transfer (conjugation) adhesion
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Conjugation
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endospores
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Important components in endospore: Calcium Dipicolinic Acid
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Sporulation
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The endospore
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Major Taxonomic Groups of Bacteria
Gracilicutes – gram-negative cell walls, thin-skinned Firmicutes – gram-positive cell walls, thick skinned Tenericutes – lack a cell wall & are soft Mendosicutes – archaea, primitive procaryotes with unusual cell walls & nutritional habits
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Grwth in Bacteria Temperature Nutrients pH Osmotic pressure
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Temperature Minimum temperature – lowest temperature that permits a microbe’s growth and metabolism Maximum temperature – highest temperature that permits a microbe’s growth and metabolism Optimum temperature – promotes the fastest rate of growth and metabolism
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3 temperature adaptation groups
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Bacterial Metabolism Phototroph Chemotroph
Photoautotroph (Photolitotroph) Photoheterotroph (Photoorganotroph) Chemotroph Chemoautotroph (Chemolitotroph Chemoheterotroph (Chemoorganotroph)
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Stages of metabolism in chemoheterotrophic bacteria
Digestion Absorption (Passive and active transportation) Preparation for oxidation Oxidation
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Oxygen requirements
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Fermentation Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen Uses organic compounds as terminal electron acceptors Yields a small amount of ATP Production of ethyl alcohol by yeasts acting on glucose Formation of acid, gas & other products by the action of various bacteria on pyruvic acid
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Fermentation
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Binary division
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Growth Curve
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Continuous Culture, Chemostat
Chemostats are a means of keeping a culture in log phase indefinitely. Continuous Culture, Chemostat
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Methods in bacterial identification
Microscopic morphology Macroscopic morphology – colony appearance Physiological / biochemical characteristics Chemical analysis Serological analysis Genetic & molecular analysis G + C base composition DNA analysis using genetic probes Nucleic acid sequencing & rRNA analysis
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Bacterial Colonies Standard Bacterial Count Colony-Forming Units
Plaque-Forming Units Spread Plate Pour Plate Soft-Agar Overlay
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Solid Medium
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