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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.