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Foundations in Microbiology Seventh Edition
Lecture PowerPoint to accompany Foundations in Microbiology Seventh Edition Talaro Chapter 4 An Introduction to the Prokaryotic Cell, Its Organization, and Members Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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4.1 Characteristics of Cells and Life
All living things (single and multicellular) are made of cells that share some common characteristics: Basic shape – spherical, cubical, cylindrical Internal content – cytoplasm, surrounded by a membrane DNA chromosome(s), ribosomes, metabolic capabilities Two basic cell types: eukaryotic and prokaryotic
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Characteristics of Cells
Eukaryotic cells: animals, plants, fungi, and protists Contain membrane-bound organelles that compartmentalize the cytoplasm and perform specific functions Contain double-membrane bound nucleus with DNA chromosomes Prokaryotic cells: bacteria and archaea No nucleus or other membrane-bound organelles
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Characteristics of Life
Reproduction and heredity – genome composed of DNA packed in chromosomes; produce offspring sexually or asexually Growth and development Metabolism – chemical and physical life processes Movement and/or irritability – respond to internal/external stimuli; self-propulsion of many organisms Cell support, protection, and storage mechanisms – cell walls, vacuoles, granules and inclusions Transport of nutrients and waste
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4.3 Prokaryotic Profiles
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Prokaryotic Profiles Structures that are essential to the functions of all prokaryotic cells are a cell membrane, cytoplasm, ribosomes, and one (or a few) chromosomes
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Figure 4.1 Structure of a bacterial cell
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4.3 External Structures Appendages Glycocalyx – surface coating
Two major groups of appendages: Motility – flagella and axial filaments (periplasmic flagella) Attachment or channels – fimbriae and pili Glycocalyx – surface coating
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Flagella 3 parts: Rotates 360o
Filament – long, thin, helical structure composed of protein Flagellin Hook – curved sheath Basal body – stack of rings firmly anchored in cell wall Rotates 360o Number and arrangement of flagella varies: Monotrichous, lophotrichous, amphitrichous, peritrichous Functions in motility of cell through environment
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Flagella
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Figure 4.2 Flagella
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Flagellar Arrangements
Monotrichous – single flagellum at one end Lophotrichous – small bunches emerging from the same site Amphitrichous – flagella at both ends of cell Peritrichous – flagella dispersed over surface of cell; slowest
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Monotrichous Lophotrichous Amphitrichous Peritrichous 13
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Flagellar Responses Guide bacteria in a direction in response to external stimulus: Chemical stimuli – chemotaxis; positive and negative Light stimuli – phototaxis Signal sets flagella into rotary motion clockwise or counterclockwise: Counterclockwise – results in smooth linear direction – run Clockwise – tumbles
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Figure 4.4 The operation of flagella
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Figure 4.5 Chemotaxis in bacteria
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Periplasmic Flagella Internal flagella, enclosed in the space between the outer sheath and the cell wall peptidoglycan Produce cellular motility by contracting and imparting twisting or flexing motion
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Periplasmic flagella on spirochete cell Electron micrograph of Borrelia burgdorferi, agent of lyme disease
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Figure 4.6 Periplasmic flagella
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Fimbriae Fine, proteinaceous, hairlike bristles emerging from the cell surface Function in adhesion to other cells and surfaces
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Fimbriae Pathogenic Escherichia coli covered with fimbriae
E. coli tightly adhere to the surface of intestinal cells with their fimbriae 21
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Pili Rigid tubular structure made of pilin protein
Found only in gram-negative cells Function to join bacterial cells for partial DNA transfer called conjugation
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Glycocalyx Coating of molecules external to the cell wall, made of sugars and/or proteins Two types: Slime layer - loosely organized and attached Capsule - highly organized, tightly attached Functions: Protect cells from dehydration and nutrient loss Inhibit killing by white blood cells by phagocytosis, contributing to pathogenicity Attachment - formation of biofilms
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Fig. 4.12 Bacillus with and without capsules
Special staining of Klebsiella highlighting the capsule
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Biofilms
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Figure 4.11 Biofilm on a catheter
Scanning electron micrograph of Staphylococcus aureus cells attached to catheter by a slime secretion
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4.4 The Cell Envelope External covering outside the cytoplasm
Composed of two basic layers: Cell wall and cell membrane Maintains cell integrity Two different groups of bacteria demonstrated by Gram stain: Gram-positive bacteria: thick cell wall composed primarily of peptidoglycan and cell membrane Gram-negative bacteria: outer cell membrane, thin peptidoglycan layer, and cell membrane
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Figure 4.12 Insert figure 4.12 Comparative cell envelopes
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Structure of Cell Walls
Determines cell shape, prevents lysis (bursting) or collapsing due to changing osmotic pressures Peptidoglycan is primary component: Unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments
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Structure of Peptidoglycan in the cell wall
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Structure of Peptidoglycan in the cell wall
Fig. 4.14c
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Peptidoglycan Lysozyme (enzyme in tears and salivia) hydrolyzes the bonds in glycan chains of invading bacteria, causing the wall to break down Several drugs including penicillin target the peptide cross-links in the peptidoglycan 33
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Gram-Positive Cell Wall
Thick, homogeneous sheath of peptidoglycan 20-80 nm thick Includes teichoic acid and lipoteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response Some cells have a periplasmic space, between the cell membrane and cell wall
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Gram-Negative Cell Wall
Composed of an outer membrane and a thin peptidoglycan layer Outer membrane is similar to cell membrane bilayer structure Outermost layer contains lipopolysaccharides and lipoproteins (LPS) Lipid portion (endotoxin) may become toxic when released during infections May function as receptors and blocking immune response Contain porin proteins in upper layer – regulate molecules entering and leaving cell Bottom layer is a thin sheet of peptidoglycan Periplasmic space above and below peptidoglycan
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Table 4.1 Comparison of Gram-Positive and Gram-Negative
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The Gram Stain Differential stain that distinguishes cells with a gram-positive cell wall from those with a gram-negative cell wall Gram-positive - retain crystal violet and stain purple Gram-negative - lose crystal violet and stain red from safranin counterstain Important basis of bacterial classification and identification Practical aid in diagnosing infection and guiding drug treatment
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Nontypical Cell Walls Some bacterial groups lack typical cell wall structure, i.e., Mycobacterium and Nocardia Gram-positive cell wall structure with lipid mycolic acid (cord factor) Pathogenicity and high degree of resistance to certain chemicals and dyes Basis for acid-fast stain used for diagnosis of infections caused by these microorganisms Some have no cell wall, i.e., Mycoplasma Cell wall is stabilized by sterols Pleomorphic
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Figure 4.15 Extreme variation in shape of Mycoplasma pneumoniae
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Cell Membrane Structure
Phospholipid bilayer with embedded proteins – fluid mosaic model Functions in: Providing site for energy reactions, nutrient processing, and synthesis Passage of nutrients into the cell and the discharge of wastes Cell membrane is selectively permeable
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Figure 4.16 Cell membrane structure
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4.5 Bacterial Internal Structures
Cell cytoplasm: Dense gelatinous solution of sugars, amino acids, and salts 70-80% water Serves as solvent for materials used in all cell functions
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Bacterial Internal Structures
Chromosome Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell Aggregated in a dense area called the nucleoid DNA is tightly coiled Minimal genetic requirement for bacterial survival
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Figure 4.17 Chromosome structure
Fluorescent staining highlights the chromosomes of bacterial pathogen, Salmonella enteriditis
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Bacterial Internal Structures
Plasmids Small circular, double-stranded DNA Free or integrated into the chromosome Duplicated and passed on to offspring Not essential to bacterial growth and metabolism May encode antibiotic resistance, tolerance to toxic metals, enzymes, and toxins Used in genetic engineering - readily manipulated and transferred from cell to cell
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Bacterial Internal Structures
Ribosomes Made of 60% ribosomal RNA and 40% protein Consist of two subunits: large and small Prokaryotic differ from eukaryotic ribosomes in size and number of proteins Site of protein synthesis Present in all cells
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Figure 4.18 Prokaryotic ribosome
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Bacterial Internal Structures
Inclusions and granules Intracellular storage bodies Vary in size, number, and content Bacterial cell can use them when environmental sources are depleted Examples: glycogen, poly b-hydroxybutyrate, gas vesicles for floating, sulfur and phosphate granules (metachromatic granules), particles of iron oxide
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Inclusions Large particles of polyhydrosybutyrate. Inclusion bodies provide long-term storage of that nutrient 53
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Bacterial Internal Structures
Cytoskeleton Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall
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Bacterial Internal Structures
Endospores Inert, resting, cells produced by some G+ genera: Clostridium, Bacillus, and Sporosarcina Have a 2-phase life cycle: Vegetative cell – metabolically active and growing Endospore – when exposed to adverse environmental conditions; capable of high resistance and very long-term survival Sporulation - formation of endospores Hardiest of all life forms Withstands extremes in heat, drying, freezing, radiation, and chemicals Not a means of reproduction Germination - return to vegetative growth
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Figure 4.22 Sporulation cycle
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Endospores Resistance linked to high levels of calcium and dipicolinic acid Dehydrated, metabolically inactive Thick coat Longevity verges on immortality, 250 million years Resistant to ordinary cleaning methods and boiling Pressurized steam at 120oC for minutes will destroy
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Medical significant endospores
Bacillus anthracis- anthrax agent, candidate of bioterrorism Clostridium genus- C. tetani - the cause of tetanus (lockjaw) C. perfringens - cause of gas gangrene (spores germinate in dead tissue, germinate, grow, and release potent toxins C. botulinum - agent of botulism, deadly form of food-poisoning 58
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4.6 Bacterial Shapes, Arrangements, and Sizes
Vary in shape, size, and arrangement but typically described by one of three basic shapes: Coccus – spherical Bacillus – rod Coccobacillus – very short and plump Vibrio – gently curved Spirillum – helical, comma, twisted rod, Spirochete – spring-like
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Figure 4.23 Common bacterial shapes
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Table 4.2 Comparison of Spiral-Shaped Bacteria
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Bacterial Shapes, Arrangements, and Sizes
Arrangement of cells is dependent on pattern of division and how cells remain attached after division: Cocci: Singles Diplococci – in pairs Tetrads – groups of four Irregular clusters Chains Cubical packets (sarcina) Bacilli: Diplobacilli Palisades
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Figure 4.25 Arrangement of cocci
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Figure 4.26 The dimensions of bacteria
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4.7 Classification Systems in the Prokaryotae
Microscopic morphology Macroscopic morphology – colony appearance Bacterial physiology/ biochemical characteristics Serological analysis- immune response Genetic and molecular analysis G + C base composition DNA analysis using genetic probes Nucleic acid sequencing & rRNA analysis
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Bacterial Taxonomy Based on Bergey’s Manual
Bergey’s Manual of Determinative Bacteriology – five volume resource covering all known prokaryotes Classification based on genetic information –phylogenetic Two domains: Archaea and Bacteria Five major subgroups with 25 different phyla
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Major Taxonomic Groups of Bacteria
Domain Archaea – primitive, adapted to extreme habitats and modes of nutrition Domain Bacteria: Phylum Proteobacteria – Gram-negative cell walls Phylum Firmicutes – mainly gram-positive with low G + C content Phylum Actinobacteria – Gram-positive with high G + C content
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Figure 4.27 Universal phylogenetic tree
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Table 4.3 General Classification Scheme
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Diagnostic Scheme for Medical Use
Uses phenotypic qualities in identification Restricted to bacterial disease agents Divides bacteria based on cell wall structure, shape, arrangement, and physiological traits
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Species and Subspecies
Species – a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly Strain or variety – a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars) Type – a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype)
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Prokaryotes with Unusual Characteristics
Free-living nonpathogenic bacteria Photosynthetic bacteria – use photosynthesis, can synthesize required nutrients from inorganic compounds Cyanobacteria (blue-green algae) Gram-negative cell walls Extensive thylakoids with photosynthetic chlorophyll pigments and gas inclusions Green and purple sulfur bacteria Contain photosynthetic pigment bacteriochlorophyll Do not give off oxygen as a product of photosynthesis Gliding, fruiting bacteria Gram-negative Glide over moist surfaces
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Figure 4.28 Structure of cyanobacteria
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Figure 4.29 Photosynthetic bacteria
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Concentrated bloom of purple sulfur bacteria
Fig. 4.34
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Fig. 4.35 Lifecycle of Chondromyces a fruiting bacteria
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Unusual Forms of Medically Significant Bacteria
Obligate intracellular parasites Rickettsias Very tiny, gram-negative bacteria Most are pathogens that alternate between mammals and blood-sucking arthropods Obligate intracellular pathogens Cannot survive or multiply outside of a host cell Cannot carry out metabolism on their own Rickettsia rickettisii – Rocky Mountain spotted fever Rickettsia typhi – endemic typhus
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TEM of the rickettsia Coxiella burntii, cause of Q fever
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Unusual Forms of Medically Significant Bacteria
Chlamydias Tiny Obligate intracellular parasites Not transmitted by arthropods Chlamydia trachomatis – severe eye infection and one of the most common sexually transmitted diseases Chlamydia pneumoniae – lung infections
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4.8 Archaea: The Other Prokaryotes
Constitute third Domain Archaea Seem more closely related to Domain Eukarya than to bacteria Contain unique genetic sequences in their rRNA Have unique membrane lipids and cell wall construction Live in the most extreme habitats in nature, extremophiles Adapted to heat, salt, acid pH, pressure, and atmosphere Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers
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Red Archea bacteria dominate the solar evaporation pond in Owens lake, CA (high salt content)
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Table 4.5 Comparison of Three Cellular Domains
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