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Bacteria: Gross Morphology and Fine Structures
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Size of a Bacteria
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Shape of Common Bacteria
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Arrangements
streptococci
sarcina
staphylococci
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Structures of a Typical Bacterial Cell
Figure 4.6a, b
Capsule
Capsule
Cell Wall
Plasma membrane
CytoplasmRibosomes
Inclusion
Cell Wall
Plasma membraneNuclear area
(nucleoid) containing DNA
Plasmid
Flagella
Fimbriae
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Structures of a Typical Bacterial Cell: Structures External to the Cell Wall
Glycocalyx
Flagella
Axial filaments
Fimbriae
Pili
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Structures External to the Cell Wall: Glycocalyx
“sugar coat”Substances that surround cellsCapsule Organized & firmly attached to the cell wall Determined by negative staining Protect pathogenic bacteria from phagocytosis
Slime layer – unorganized & only loosely attached to the cell wall
Figure 4.6a, b
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Structures External to the Cell Wall: Flagella
“whip”
Long filamentous appendages that propel bacteria
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Structures External to the Cell Wall: Flagella
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Structures External to the Cell Wall: Flagellar Arrangement
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Structures External to the Cell Wall: Axial Filaments
Endoflagella
In spirochetes
Anchored at one end of a cell
Rotation causes cell to move
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Structures External to the Cell Wall: Fimbriae and Pili
Fimbriae – enable a cell to adhere to surfaces
Pili – used to transfer DNA from one cell to another
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The Cell Wall
A complex, semi-rigid structure responsible for the shape of the cell
Functions: Prevents osmotic lysis Helps maintain the shape of the bacterium Serves as point of anchorage for flagella Contributes to microorganisms’ pathogenicity Site of action of some antibiotics Used to differentiate major types of bacteria
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The Cell Wall: Composition & Characteristics
Made of peptidoglycan Polymer of N-acetylglucosamine (NAG) & N-
acetylmuramic acid (NAM) = glycan part Linked by polypeptides = peptide part
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The Cell Wall: Composition & Characteristics
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Gram-positive and gram-negative bacteria
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The Cell Wall: Composition & Characteristics
Gram Positive Gram Negative
Color of Gram-stained cell Purple Reddish pink
Representative genera Bacillus, Staphylococcus
Escherichia, Pseudomonas
Distinguishing Characteristics/Components
Peptidoglycan Thick layer Thin layer
Teichoic acid Present Absent
Periplasm Absent Present
Outer Membrane Absent Present
Endotoxin (lipopolysaccharide) Absent Present
Porin proteins Absent Present
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The Cell Wall: Composition & Characteristics
Gram Positive Gram Negative
General Characteristics
Sensitivity to penicillin
Generally more susceptible
(with notable exceptions)
Generally less susceptible
(with notable exceptions)
Sensitivity to lysozyme
Yes No (unless treated also with EDTA)
Form that results from removal of peptidoglycan
Protoplast Spheroplast
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The Cell Wall:Atypical Cell Walls
Mycoplasmas Smallest known bacteria that can grow &
reproduce outside living host cells Lack cell walls Sterols in plasma membrane
Archaea Wall-less, or Walls of pseudomurein (lack NAM and D
amino acids)
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Structures Internal to the Cell Wall:Plasma Membrane
Thin structure lying inside the cell wall & enclosing the cytoplasm of the cell
Consists mostly of phospholipids & proteins
Functions: Selective permeability Breakdown of nutrients ATP production
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Structures Internal to the Cell Wall:Plasma Membrane
Structures
Phospholipid bilayer
Peripheral proteins
Integral proteins
Transmembrane proteins
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Structures Internal to the Cell Wall:Cytoplasm
Substance inside the plasma membrane80% waterContains proteins, carbohydrates, lipids, inorganic ions & low-molecular weight compoundsStructures: DNA, ribosomes, inclusionsProkaryotic cytoplasm lacks cytoskeleton & cytoplasmic streaming
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Structures Internal to the Cell Wall:Nuclear Area (Nucleoid)
Contains bacterial chromosome & plasmids
Bacterial chromosome Cell’s genetic information No histones & nuclear envelope
Plasmids Extrachromosomal genetic elements Not connected to the bacterial chromosome Replicate independently of chromosomal DNA
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Structures Internal to the Cell Wall:Ribosomes
Sites of protein synthesis
Composed of 2 subunits: each consists of protein & rRNA
Prokaryotic ribosomes smaller & less dense
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Structures Internal to the Cell Wall:Inclusions
Metachromatic granules
Polysaccharide granules
Lipid inclusions
Sulfur granules
Carboxysomes
Gas vacuoles
Magnetosomes
Phosphate reserves
Energy reserves
Energy reserves
Energy reserves
Ribulose 1,5-diphosphate carboxylase for CO2 fixation
Protein covered cylinders
Iron oxide (destroys H2O2)
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Inclusions
Inclusions are aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell.
Inclusions accumulate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions
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Structures Internal to the Cell Wall:Endospores
Bacillus, Clostridium
Resting cells
Resistant to desiccation, heat, chemicals
Sporulation: Endospore formation
Germination: Return to vegetative state
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End
ospo
res
Form inside of vegetative cells (hence “endo”).
Highly resistant to heat, U.V.,
desiccation, etc.
Characteristic of many soil bacteria, e.g., Bacillus spp. & Clostridium spp.
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References
Talaro KP. (1999). Talaro KP. (1999). Foundations in Microbiology: An Introduction.Foundations in Microbiology: An Introduction. (1994). USA: The Benjamin/Cummings Publishing Company, Inc.(1994). USA: The Benjamin/Cummings Publishing Company, Inc.
Tortora GJ, BR Funke & CL Case. (1995). Tortora GJ, BR Funke & CL Case. (1995). Microbiology: An Microbiology: An Introduction.Introduction. Bridge Parkway, CA: The Benjamin Cummings Bridge Parkway, CA: The Benjamin Cummings Publishing Company, Inc.Publishing Company, Inc.
Masserrat, E., Lu, P., and Taucher, J. Masserrat, E., Lu, P., and Taucher, J. Using Morphology Using Morphology Characteristics to Study Bacterial Diversity, Characteristics to Study Bacterial Diversity, Pennsylvania State Pennsylvania State UniversityUniversity
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Acknowledgment
DFCornago, Instructor, Department of Food Science and Nutrition, College of Home Economics, University of the Philippines, Diliman.