1. Universal phylogenetic tree1 1

2. Classification Systems in the Prokaryotae
Microscopic morphology
Macroscopic morphology – colony appearance
Bacterial physiology
Serological analysis
Genetic and molecular analysis 2 2

3. 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 3 3

4. 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) 4 4

5. 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

6. 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

7. Comparison of Three Cellular Domains7 7

8. Prokaryotic Profiles

9. 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

10. 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 10 10

11. Cell membrane structure11 11

12. Membrane Lipids

13. Structure of a bacterial cell

14. 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

15. Peptidoglycan

16. 16 16

17. 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

18. 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 18 18

19. 19 19

20. Comparison of Gram-Positive and Gram-Negative20 20

21. 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 21 21

22. 22 22

23. 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 23 23

24. Extreme variation in shape of Mycoplasma pneumoniae24 24

25. 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 25 25

26. 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 26 26

27. Chromosome structure 27 27

28. 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 28 28

29. Random microbe of the week!!!
Serratia marcescens

30. 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 30 30

31. Prokaryotic ribosome 31 31

32. 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, sulfur and phosphate granules, particles of iron oxide 32 32

33. Cytoskeleton
Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall 33 33

34. 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 34 34

35. Common bacterial shapes35 35

36. Comparison of Spiral-Shaped Bacteria36 36

37. Bacterial Arrangements
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 37 37

38. Arrangement of cocci 38 38

39. Arrangement of bacilli

40. 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

41. 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

42. Flagella

44. 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

45. Electron micrographs of flagellar arrangements

46. 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

47. The operation of flagella

48. Chemotaxis in bacteria

49. 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

50. Periplasmic flagella

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

52. 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

53. 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

56. Biofilm on a catheter

57. 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

58. Archaea

59. Comparison of Three Cellular Domains