1. BACTERIAL STRUCTURE

2. The gross morphological characteristics of bacterial cells…
Size, Shape, Structure, Arrangement
Pairs, Clusters, Trichomes, Filaments

3. Size Bacteria are very small: ~ 0.5 to 1.0 μm in diameter.
The surface area to volume ratio of bacteria is exceedingly high comparitively.
A relatively large surface through which nutrients can enter (or waste products leave) compared to a small volume of cell substance to be nourished.
 Unusually high growth rate and metabolism of bacteria.

4. Because of the high surface area-volume ratio, the mass of cell substance to be nourished is very close to the surface; therefore, no circulatory mechanism is needed to distribute the nutrients that are taken in.

5. Shape and Arrangement Shape determined by its rigid cell wall
Typical bacterial cells are
Spherical (cocci; coccus)
Straight rods (bacilli; bacillus)
Helically curved Rods (spirilla; spirillum)
Some cells are “Pleomorphic”

6. Staphylococcus

7. Lactobacillus

8. Aquaspirillum

9. Pleomorphic Arthrobacter

10. Characteristic arrangements of cocci
Diplococci:
Cells divide in one plane and remain attached predominantly in pairs.
Streptococci:
Cells divide in one plane and remain attached to form chains.
Tetracocci:
Cells divide in two planes and characteristically form groups of four cells.
Staphylococci:
Cells divide in three planes, in an irregular pattern, producing “bunches” of cocci.
Sarcinae:
Cells divide in three planes, in a regular pattern, producing a cuboidal arrangement of cells

13. Diplococci

14. Streptococci (Chains)

15. Tetracocci

16. Staphylococci (Bunches)

17. Sarcinae (Cuboidal Packets)

18. Arrangements in Bacilli
Diplobacilli: Pairs of Bacilli
Streptobacilli: Chain formation. Eg. B.subtilis
Trichomes: Eg. Beggiotoa and Saprospira sp.
Similar to chains but with much larger area of contact between the adjacent cells
Pallisade: Eg. Corynebacterium diphtheriae
Cells are lined side by side like matchsticks and at angles to one another.
Hyphae and Mycelia: Eg. Streptomyces species
Long, branched, multinucleate filaments called hyphae which collectively form a mycelium
Note: Hyphae and mycelium are also commonly applied to the filaments formed by fungi.

20. Saprospira

21. Corynebacterium diphtheriae

22. Arrangements in Curved bacteria
Usually curved with 1 twist.
Vibrioid shape: Bacteria with less than 1 complete twist
Helical Shape: Bacteria with one or more complete turns have a helical shape. Eg. Spirilla are rigid helical bacteria, Spirochetes are highly flexible.

24. Uncommon Shapes & Arrangements
Pear-shaped cells (e.g.. Pasteuria)
Lobed spheres (e.g.. Sulfolobus)
Rods with squared rather than the usual hemispherical ends (e.g. B.anthracis)
Disks arranged like stacks of coins (e.g.. Caryophanon)
Rods with helically sculptured surfaces (e.g.. Seliberia)

26. STRUCTURES EXTERNAL TO THE CELL WALL
In bacteria,
STRUCTURES
EXTERNAL
TO THE CELL WALL

27. FLAGELLA Singular: Flagellum
A long, slender, helical appendage from the cell body, composed of microtubules, protruding through the cell wall
In prokaryotes, responsible for swimming motility to propel the cell by beating in a whip-like motion
In larger animals, they often serve to move fluids along mucous membranes such as the lining of the trachea
0.01 to 0 02 μm in diameter
Location on the cell varies depending on the bacterial species
At polar region(s): At one or both ends of the bacterium
At lateral regions: Along the sides of the bacterium

28. Monotrichous: A single polar flagellum Eg.: Pseudomonas aeruginosa

29. Lophotrichous: A cluster of polar flagella Eg.: Psedomonas fluorescens

30. Amphitrichous: Either single or clusters, at both cell poles. Eg
Amphitrichous: Either single or clusters, at both cell poles. Eg.: Aquaspirillum serpens

31. Peritrichous: Surrounded by lateral flagella Eg.: Salmonella typhi

32. A flagellum is composed of three parts:
A basal body associated with the cytoplasmic membrane and cell wall
A short hook
A very long helical filament
Some Gram-negative bacteria have a sheath surrounding the flagellum: this sheath is continuous with the outer membrane of the Gram-negative cell wall.
The hook and filament are composed of protein monomers arranged helically
The protein of the filament is known as flagellin.

34. The flagellar motor is driven by the protonmotive force. i. e
The flagellar motor is driven by the protonmotive force. i.e.. the force derived from the electrical potential and the hydrogen-ion gradient across the cytoplasmic membrane.
The concentration of cGMP (cyclic guanosine 3’,5’- phosphoric acid) within the cell governs the direction in which the rotation occurs.

35. Bacteria having polar flagella swim in a back-and-forth fashion; They reverse their direction of swimming by reversing the direction of flagellar rotation.

36. Motility without flagella
No external flagella in certain helical bacteria (spirochetes)
Have flagella-like structures located within the cell.
Just beneath the outer cell envelope.
Called Periplasmic flagella or Axial fibrils or Endoflagella.
Other helical bacteria called spiroplasmas lack any apparent organelles for motility, even periplasmic flagella.
Yet, swims in viscous media; Mechanism unknown.

37. Chemotaxis
Capability of directed swimming toward or away from various chemical compounds: Bacterial chemotaxis.
Swimming toward a chemical is termed positive chemotaxis; swimming away is negative chemotaxis.
A change in the concentration of the chemical with time, i.e., a temporal gradient.
Gradients sensed by means of protein chemoreceptors, located on the cytoplasmic membrane
Receptors, specific for different attractants and repellents.
Continuous comparison with its immediate environment with the environment it had experienced a few moments ago.

38. Phototaxis Exhibited by phototrophic bacteria
Positive: Motion towards increasing light intensities
Negative: Motion repelled by decreasing light intensities.

39. Magnetotaxis
Exhibits directed swimming in response to the earth’s magnetic field or to local magnetic fields
Eg.: Aquaspirillum magnetotacticum
Due to a chain of magnetite inclusions (magnetosomes) within the cell
Cell becomes oriented as a magnetic dipole.
Found in regions where there is a downward inclination of the Earth’s magnetic field in the regions where these bacteria have been found
May serve to direct the cells downward in aquatic environments toward oxygen-deficient areas more favorable for growth.

40. PILI (FIMBRIAE)
Pilus: Hollow, nonhelical, filamentous appendages that are thinner, shorter & and more numerous than flagella
Not for motility
Found on nonmotile as well as motile species
Different types of pili
F pilus (or sex pilus): Serves as the port of entry of genetic material during bacterial mating
For allowing pathogenic bacteria to attach to epithelial cells lining the respiratory, intestinal, or genitourinary tracts, in human infection.
To prevent the bacteria from being washed away by the flow of mucous or body fluids and permits the infection to be established.

43. CAPSULE A viscous substance forming an envelope around the cell wall
Consist of a mesh or network of fine strands.
May or may not be soluble in water.
Microcapsule: If the layer is too thin to be seen by light microscopy
Slime: If it is abundant
Many cells embedded in a common matrix.

44. Function (dependent on the bacterial spp)
Provides protection against temporary drying by binding water molecules
Blocks attachment of bacteriophages
Antiphagocytic i.e., they inhibit the engulfment of pathogenic bacteria by WBCs, so, contributes to virulence
Promote attachment of bacteria to surfaces
Eg.: Streptococcus mutans, produces dental caries; firmly adheres to the smooth surfaces of teeth because of its secretion of a water-insoluble glucan
May promote stability of bacterial suspension by preventing the cells from aggregating and settling out
Only if capsules are composed of compounds with an electrical charge
Cells bearing similarly charged surfaces repel.

45. Capsules are usually composed of polysaccharides.
If composed of a single kind of sugar: “Homopolysaccharides”
Eg.: Synthesis of glucan (a polymer of glucose) from sucrose by S. mutans
If composed of several kinds of sugars: “Heteropolysaucharides”
Eg.: Capsule of Klebsiella pneumoniae
Some polypeptide capsules
Eg.: Capsule of Bacillus anthracis – a polymer of Glu

46. SHEATH Some bacterial spp. esp.from freshwater and marine environments
Formation of Chains or trichomes enclosed by a hollow tube called a Sheath.
May sometimes contain ferric or manganese hydroxides.

47. Prosthecae Semirigid extensions of the cell wall and cell membrane
Present in aerobic bacteria from freshwater and marine sources
Eg. Caulobacter (1 prostheca), Stella & Ancalomicrobium (many)
Increases the surface area of the cells for nutrient absorption
May form a new bud at the end of a prostheca
May aid in attachment to surfaces using an adhesive substance at the end of a prostheca.

48. CELL WALL Surrounding the cytoplasmic membrane
Highly rigid structure giving shape to the cell
Prevents the cell from expanding and eventually bursting because of uptake of water
Hypotonic environments (environments having a lower osmotic pressure than exists within the bacterial cells)

49. Among the ordinary or typical bacteria (eubacteria)
Gram-negative species: Generally thinner walls (10 to 15 nm)
Gram-positive species: Thicker walls (20 to 25 nm)

50. Shape is determined by peptidotglycan / murein)
Composition:
Shape is determined by peptidotglycan / murein)
An insoluble, porous, cross-linked polymer – strong and rigid.
A polymer of N-acetylglucosamine, N-acetylmuramic acid, L-Ala, D-Ala, D-Glu and a diamino acid.
A diamino acid: LL- or meso-diaminopimelic acid, L-lysine, L-ornithine, or L-diaminobutyric acid

51. In archaeobacteria Possess cell walls, but NO peptidoglycan
Usually composed of proteins, glycoproteins, or polysaccharides.

52. Gram-positive bacteria
Have a much greater amount of peptidoglycan.
Accounts for > 50% of the dry weight of the wall of some Gram-positive species.

53. Most Gram-positive bacteria contain very little lipid.
Teichoic acid.
Eg.: Staphylococcus aureus and Streptococcus faecalis
Acidic polymers of ribitol phosphate or glycerol phosphate, covalently linked to peptidoglycan
Binds magnesium ions.
Protects bacteria from thermal injury.
Also, polysaccharides, covalently linked to the peptidoglycan. Eg.: Streptococcus pyogenes.
Most Gram-positive bacteria contain very little lipid.
Exceptions: Mycobacterium, Corynebacterium

54. Gram-negative bacteria
More complex than those of Gram-positive bacteria.
A 8 nm-thick outer membrane surrounds a thin underlying layer of peptidoglycan.
Rich in lipids (11 to 22% of cell wall dry weight).
Serves as an impermeable barrier to prevent the escape of important enzymes, such as those involved in cell wall growth, from the periplasmic space.
Serves as a barrier to external chemicals and enzymes that may damage the cell.
The space between the cytoplasmic membrane and the outer membrane (periplasmic space).

55. The LPS has toxic properties: Endotoxin.
Outer membrane held to peptidoglycan by means of Braun’s lipoprotein (5-7 nm thick layer)
A bilayered structure consisting mainly of phospholipids, proteins & LPS.
The LPS has toxic properties: Endotoxin.
Occurs only in the outer layer of the outer membrane
Composed of 3 covalently linked parts
Lipid A, firmly embedded in the membrane
Core polysaccharide, located at the membrane surface
Polysaccharide O antigens - extend from the membrane surface into the surrounding medium.

56. Also serve as receptors for bacteriophage attachment.
Porins: Membrane-spanning channel protein – To allow nucleosides, mono and oligosaccharides, peptides & amino acids, to pass across
Different porins, specific for different classes of small molecules

57. STRUCTURES INTERNAL TO THE CELL WALL
In bacteria,
STRUCTURES
INTERNAL
TO THE CELL WALL

58. Cytoplasmic Membrane:
Immediately beneath the cell wall.
~ 7.5 nm thick
Composed primarily of phospholipids (about %) & proteins (about %).
A hydrophobic barrier to penetration by most water-soluble molecules.
Contains various enzymes involved in respiratory metabolism and in synthesis of capsular and cell-wall components.
Impermeable to protons (H+ ions).

59. Other proteins are only loosely attached (peripheral proteins)
Phospholipids form a bilayer in which most of the proteins are held (integral proteins)
Other proteins are only loosely attached (peripheral proteins)
Lipid matrix of the membrane has Fluidity, allowing the components to move around laterally.
Fluidity dependent on factors such as temperature and on the proportion of unsaturated fatty acids to saturated fatty acids present in the phospholipids.

60. ln eubacteria, the phospholipids are phosphoglycerides:
Straight-chain fatty acids are ester-linked to glycerol.
ln archaeobacteria, the phospholipids are polyisoprenoid branched-chain lipids:
Long-chain branched alcohol (phytanols) are ether-linked to glycerol.

62. Proteins, synthesized within the cell, passing across the cell membrane:
Protein components of cell walls – Porins, Lipoproteins
Exocellular enzymes – penicillinases, proteinases and amylases.
Proteins remaining back – Cytochromes, Dehydrogenases

63. PROTOPLAST
Portion of a bacterial cell consisting of the cytoplasmic membrane and the cell material bounded by it.
Can be prepared from Gram-positive bacteria
By treating the cells with an enzyme such as lysozyme, which selectively dissolves the cell wall
By culturing the bacteria i.p.o. an antibiotic such as penicillin, which prevents the formation of the cell wall.
To protect the organisms from bursting.
Bursting can be prevented by preparing protoplasts in an isotonic medium, i.e., in a medium that has an osmotic pressure similar to that of the protoplast.

64. SPHEROPLAST Round, osmotically fragile forms of Gram-negative bacteria
Prepared by similar procedures
Has two membranes, the cytoplasmic membrane of the protoplast plus the outer membrane of the cell wall.

65. Membranous Intrusions
Mesosomes
Membrane invaginations as Convoluted tubules and vesicles.
Central mesosomes: Penetrate deeply; Located near the middle of the cell; Attached to the cell’s nuclear material; Involved in DNA replication and cell division
Peripheral mesosomes: Shallow penetration; No association with nuclear material: Involved in export of exocellular enzymes.

66. Intracellular membrane systems
In Methane-oxidizing bacteria, in some chemoautotrophic bacteria & phototrophic bacteria.
To increase surface area for various metabolic activities.
Eg.: Thylakoids in Cyanobacteria.

67. CYTOPLASM
The area enclosed by the cvtoplasmic membrane may be divided into
Cytoplasmic area, granular in appearance and rich in the macromolecular RNA-protein bodies: Ribosomes
Chromatinic area, rich in DNA
The fluid portion with dissolved substances.

68. Volutin / Metachromatic granules:
Composed of polyphosphate.
Serves as a reserve source of phosphate.
Poly-β-hydroxybutyrate. (PHB):
In aerobic bacteria
Serves as a reserve carbon and energy source.
Gas vacuoles:
Bacteria living in aquatic habitats
To provide buoyancy.

69. SPORES
A metabolically dormant form which, under appropriate conditions, can undergo germination and outgrowth to form a vegetative cell.
Certain species of bacteria produce spores.
Within the cell (endospores) or
External to the cell (exospores).

70. ENDOSPORES
Thick-walled, highly refractile bodies that are produced one per cell
Formed by Bacillus, Clostridium, Sporosarcina, Thermoactinomyces
Extremely resistant to desiccation, staining, disinfecting chemicals, radiation, and heat.
Average degree of heat resistance of endospores: upto 80°C for 10 min.
Dehydration occurs: Most water in the developing spore is expelled
Contain abundant dipicolinic acid (DPA) in combination with large amounts of calcium
Calcium-DPA complex – a role in the heat resistance of endospores.

71. EXOSPORES Cells of the methane-oxidizing genus Methylosinus
Form spores external to the vegetative cell, by budding at one end of the cell.
Desiccation- and heat-resistant.
No DPA.

72. Actinomycetes form branching hyphae.
From hyphal tips, spores form by crosswall formation (septation).
Spores develop, singly or in chains.
Spores contained in an enclosing sac called Sporangium: Sporangiospores
Else, Conidiospores (or conidia).The spores do not have the high heat resistance of endospores, but they can survive long periods of drying.

73. CYSTS
Dormant, thick-walled, desiccation-resistant forms that develop by differentiation of a vegetative cell and which can later germinate under suitable conditions
Resemble endospores
Structure and chemical composition are different
Do not have the high heat resistance of endospores.
Eg.: cysts of Azotobacter genus.