Classification of bacteria
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Classification of Bacteria. Differentiation of Bacteria by Cell Wall Composition. Bacteria Cell Walls. The cell wall is the outer most layer of the cell. In many cases the cell wall comes in direct contact with the environment. Function Protection of the cell

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Classification of Bacteria

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Classification of bacteria

Classification of Bacteria

Differentiation of Bacteria by

Cell Wall Composition


Bacteria cell walls

Bacteria Cell Walls

The cell wall is the outer most layer

of the cell. In many cases the cell

wall comes in direct contact with the

environment.

Function

  • Protection of the cell

  • Maintains the shapes of the cell

  • Maintains the osmotic integrity of the cell


Bacterial cell walls

Bacterial Cell Walls

  • Provide structure and shape and protect cell from osmotic forces

  • Assist some cells in attaching to other cells or in eluding antimicrobial drugs

  • Not present in animal cells, so can target cell wall of bacteria with antibiotics

  • Bacteria and archaea have different cell wall chemistry


Bacterial morphology

Bacterial Morphology


Morphology relation to cell wall composition

Morphology Relation to Cell Wall Composition

Consider the three morphological

distinctions of bacteria.

Which of these shapes would need

to be flexible in order to exhibit

the shape of the bacterium?


Bacteria cell walls1

Bacteria Cell Walls

Bacteria are classified into

two groups based on the

composition of their cell

walls.

The two groups are known as

gram positive and gram negative.


Bacterial cell walls1

Bacterial Cell Walls

  • Most have cell wall composed of peptidoglycan

  • Peptidoglycan is composed of sugars, NAG, and NAM

  • Chains of NAG and NAM attached to other chains by tetrapeptide crossbridges

    • Bridges may be covalently bonded to one another

    • Bridges may be held together by short connecting chains of amino acids


Gram positive cell wall

Gram Positive Cell Wall

Gram-positive cell walls

  • Relatively thick layer of peptidoglycan

  • Contain unique polyalcohols called teichoic acids

    • Some covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane

  • Retain crystal violet dye in Gram staining procedure; so appear purple


Gram positive cell wall1

Gram Positive Cell Wall

The gram positive cell wall is referred to as a peptidoglycan

layer and is composed of alternating subunits of two

carbohydrates: n-acetyl muramic acid and n-acetyl glucosamine.


Gram positive cell wall2

Gram Positive Cell Wall

The gram positive cell wall is referred to as a peptidoglycan

layer and is composed of alternating subunits of two carbohydrates:

n-acetyl muramic acid (NAM) and n-acetyl glucosamine (NAG).


Gram negative cell wall

Gram Negative Cell Wall

  • Gram-negative cell walls

    • Have only a thin layer of peptidoglycan

    • Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)

    • May be impediment to the treatment of disease

    • Appear pink following Gram staining procedure


Gram negative cell wall1

Gram Negative Cell Wall

The gram negative cell wall consists of two distinct layers. The

outer most layer is referred as the outer membrane and is

composed of lipopolysaccarhides (LPS). The second layer a

peptidoglycan layer that is homologous to a gram positive cell

wall.


Comparison of gram negative and gram positive cell walls

Comparison of Gram Negative and Gram Positive Cell Walls


Application of cell wall difference

Application of Cell Wall Difference

Why does the gram stain work?

How is the differences of cell wall

types used to distinguish the

different bacterial types?


Application of cell wall difference1

Application of Cell Wall Difference

Scenario

You have been give a slide with a mixture of gram positive

(coccus) and gram negative bacteria (spirochete).

Think about the gram stain procedure as it relates to the

cell wall differences. What would the end result of each

step of the gram stain be for each of the bacteria types?


Application of cell wall difference2

Application of Cell Wall Difference

Gram Staining Procedure

ReagentFunction Results

Crystal VioletPrimary Stain

IodineMordant

Acetone-AlcoholDecolorizer

SafraninCounter Stain


Results of the gram stain

Results of the Gram Stain


Conclusion

Conclusion

Why does the gram stain work?

Because of the differences of cell wall composition.


Conclusion1

Conclusion

The gram positive cell wall is referred to as a peptidoglycan

layer and is composed of alternating subunits of two

carbohydrates: n-acetyl muramic acid and n-acetyl

glucosamine.

The gram negative cell wall consists of two distinct layers.

The outer most layer is referred as the outer membrane and

is composed of lipopolysaccarhides (LPS). The second layer

a peptidoglycan layer that is homologous to a gram positive

cell wall.


Comparison of gram negative and gram positive cell walls1

Comparison of Gram Negative and Gram Positive Cell Walls


Prokaryotic cell walls

Prokaryotic Cell Walls

  • Archaeal Cell Walls

    • Do not have peptidoglycan

    • Contains variety of specialized polysaccharides and proteins

    • Gram-positive archaea stain purple

    • Gram-negative archaea stain pink


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