The Bacterial Cell

The Bacterial Cell

Dr. Alvin Fox

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Key Words Prokaryotic Eubacteria (Bacteria) Archaebacteria (Archaea) Eukaryotic Plasmid Chromosome Ribosome Peptidoglycan (murein, mucopeptide) Gram stain Gram negative Gram positive Cell envelope Cell membrane Cell wall

Outer membrane Periplasmic space Oxidative phosphorylation Spheroplast/protoplast Flagella Chemotaxis Axial filament Periplasmic binding protein Permeases Storage Granules Pili (fimbriae) Capsule (slime layer, glycocalyx) Endospore (spore) 2

EUKARYOTES PROKARYOTES

BACTERIA ARCHAEA 3

Prokaryotes (Bacteria) • Eubacter "True" bacteria – – –

human pathogens clinical or environmental one kingdom

• Archaea – Environmental organisms – second kingdom 4

Eukaryotes • Other cell-based life e.g. – plants – animals – fungi

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Prokaryotic Cell (versus Eukaryotic Cell) • • • •

Not compartmentalized Cell membranes lack sterols (e.g. cholesterol) Single circular chromosome Ribosomal are 70S - subunits • •

30S (16S rRNA) 50S (5S & 23S rRNA)

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Bacteria versus Archaebacteria • Eubacteria – peptidoglycan (murein) – muramic acid • Archaebacteria – pseudomurein – no muramic acid

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Bacteria versus Archaebacteria • 16S rRNA – sequence different

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Eukaryotic cell

Prokaryotic cell Gram + Flagellum

(e.g. animal) Rough endoplasmic reticulum Nucleus

Cell membrane

Nucleoid

Cell wall

Gram Pili

Cytoplasm Mitochondria

Capsule

Granule

Cell (inner) membrane Outer membrane 9 Ribosomes Cell wall

Bacteria

• Plasmids

• Extra-chromosomal DNA • multiple copy number • coding - pathogenesis factors - antibiotic resistance factors

• bacterial replication

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The Cell Envelope

Gram Positive

Gram Negative

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Oxidative phosphorylation occurs at cell membrane (since there are no mitochondria).

Cell Wall

Cytoplasm

Cell membrane

The cell wall is outside of cell membrane – rigid, protecting cell from osmotic lysis.

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GRAM POSITIVE Lipoteichoic acid

Peptidoglycan-teichoic acid

Cytoplasmic membrane

Cytoplasm

GRAM NEGATIVE Periplasmic space

Porin

Outer Membrane

Lipopolysaccharide

Braun lipoprotein

Inner (cytoplasmic) membrane

Cytoplasm

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Outer Membrane • •

• •

Gram negative bacteria major permeability barrier space between inner and outer membrane – periplasmic space store degradative enzymes Gram positive bacteria no periplasmic space 14

GRAM NEGATIVE CELL ENVELOPE Outer Membrane (Major permeability barrier)

Porin

Lipopolysaccharide

Braun lipoprotein

Periplasmic space Inner (cytoplasmic) membrane

Degradative enzyme Periplasmic binding protein

Cytoplasm

Permease

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GRAM POSITIVE CELL ENVELOPE Degradative enzyme

Lipoteichoic acid

Peptidoglycan-teichoic acid

Cytoplasmic membrane

Cytoplasm

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FLAGELLA • • • •

Some bacteria are motile Locomotory organelles- flagella Taste environment Respond to food/poison – chemotaxis 17

• Flagella – embedded in cell membrane – project as strand – Flagellin (protein) subunits – move cell by propeller like action

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Axial filaments – spirochetes – similar function to flagella – run lengthwise along cell – snake-like movement

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Making Wall-less forms •

Result from action of: – enzymes lytic for cell wall – antibiotics inhibiting peptidoglycan biosynthesis

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Usually non-viable

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Wall-less bacteria that don’t replicate: – spheroplasts (with outer membrane) – protoplasts (no outer membrane).

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Wall-less bacteria that replicate – L forms 20

Naturally Wall-less Genus • Mycoplasma

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Pili (fimbriae) • hair-like projections of the cell • sexual conjugation • adhesion to host epithelium

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Capsules and slime layers • • • • • •

outside cell envelope well defined: capsule not defined: slime layer or glycocalyx usually polysaccharide often lost during in vitro culture protective in vivo

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Endospores (spores) • • •

Dormant cell Produced when starved Resistant to adverse conditions - high temperatures - organic solvents • contain calcium dipicolinate • Bacillus and Clostridium 24