Foundations in Microbiology Seventh Edition

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1 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.

2 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 2

3 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 3

4 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 4

5 4.3 Prokaryotic Profiles 5

6 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 6

7 Figure 4.1 Structure of a bacterial cell 7

8 4.3 External Structures Appendages Two major groups of appendages: Motility flagella and axial filaments (periplasmic flagella) Attachment or channels fimbriae and pili Glycocalyx surface coating 8

9 3 parts: Flagella Filament long, thin, helical structure composed of protein Flagellin Hook curved sheath Basal body stack of rings firmly anchored in cell wall Rotates 360 o Number and arrangement of flagella varies: Monotrichous, lophotrichous, amphitrichous, peritrichous Functions in motility of cell through environment 9

10 Figure 4.2 Flagella 10

11 Flagellar Arrangements 1. Monotrichous single flagellum at one end 2. Lophotrichous small bunches emerging from the same site 3. Amphitrichous flagella at both ends of cell 4. Peritrichous flagella dispersed over surface of cell; slowest 11

12 Figure 4.3 Electron micrographs of flagellar arrangements 12

13 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 13

14 Figure 4.4 The operation of flagella 14

15 Figure 4.5 Chemotaxis in bacteria 15

16 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 16

17 Figure 4.6 Periplasmic flagella 17

18 Fimbriae Fine, proteinaceous, hairlike bristles emerging from the cell surface Function in adhesion to other cells and surfaces 18

19 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 19

20 Glycocalyx Coating of molecules external to the cell wall, made of sugars and/or proteins Two types: 1. Slime layer - loosely organized and attached 2. 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 20

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23 Figure 4.11 Biofilm on a catheter 23

24 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 24

25 Figure 4.12 Insert figure 4.12 Comparative cell envelopes 25

26 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 26

27 Figure 4.13 Peptidoglycan 27

28 Gram-Positive Cell Wall Thick, homogeneous sheath of peptidoglycan 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 28

29 Figure

30 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 30

31 31

32 Table 4.1 Comparison of Gram-Positive and Gram-Negative 32

33 The Gram Stain Differential stain that distinguishes cells with a grampositive 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 33

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35 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 35

36 Figure 4.15 Extreme variation in shape of Mycoplasma pneumoniae 36

37 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 37

38 Figure 4.16 Cell membrane structure 38

39 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 39

40 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 40

41 Figure 4.17 Chromosome structure 41

42 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 42

43 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 43

44 Figure 4.18 Prokaryotic ribosome 44

45 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 45

46 Figure 4.19 Bacterial inclusion bodies 46

47 Bacterial Internal Structures Cytoskeleton Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall 47

48 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 48

49 Figure 4.22 Sporulation cycle 49

50 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 120 o C for minutes will destroy 50

51 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 51

52 Figure 4.23 Common bacterial shapes 52

53 Table 4.2 Comparison of Spiral-Shaped Bacteria 53

54 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 Chains Palisades 54

55 Figure 4.25 Arrangement of cocci 55

56 Figure 4.26 The dimensions of bacteria 56

57 4.7 Classification Systems in the Prokaryotae 1. Microscopic morphology 2. Macroscopic morphology colony appearance 3. Bacterial physiology 4. Serological analysis 5. Genetic and molecular analysis 57

58 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 58

59 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 59

60 Figure 4.27 Universal phylogenetic tree 60

61 Table 4.3 General Classification Scheme 61

62 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 62

63 63

64 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) 64

65 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 65

66 Figure 4.28 Structure of cyanobacteria 66

67 Figure 4.29 Photosynthetic bacteria 67

68 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 68

69 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 69

70 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 70

71 Archaea 71

72 Table 4.5 Comparison of Three Cellular Domains 72

An Introduction to the Prokaryotic Cells. BIO370 Dr. Ramos

An Introduction to the Prokaryotic Cells BIO370 Dr. Ramos Characteristics of Cells and Life All living things (single and multicellular) are made of cells that share some common characteristics: Basic