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Bacteria
BIO162 Fall 07
Page Baluch
Domain Bacteria
Differences (cell types, metabolism, etc) between microbes:
Are results of evolution from a common ancestor
Survival of the fittest for a specific environment
Bergey’s Manual names ~ 5000 bacterial species (only 1% of
existing bacteria!)
Characteristics used in microbial classification include:
Cell shape, staining reaction, motility, colony morphology,
atmospheric & nutrients requirements, biochemical & metabolic
activity, enzymes, pathogenicity, genetic material
Three main phenotypic categories:
Gram-negative
Gram-positive
Gram-variable (no cell wall)
Morphology (cell shape)
Three major
shapes:
Cocci (round)
Bacilli (rod)
spirilla (spiral or
curved)
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Morphology
Grouping of cocci and bacilli
Sometimes you can tell the shape of the bacteria
from their names, but not always (Table 4-6)
Cell shape Example
Cocci
Streptococcus pyogenes
Staphylococcus aureus
Neisseria gonorrhoeae
Bacilli
Bacillus anthracis
Clostridium sp.
Escherichia coli
Salmonella sp.
Mycobacterium sp.
Pleomorphic
Mycoplasma pneumonae
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Staining procedures enable us to see
and identify bacteria
Simple stain – sufficient to determine cell
shape and morphological arrangement e.g
methylene blue
Differential stain - differentiate bacteria
based on composition of cell wall e.g Gramstain, Acid-fast stain
Special stain
Structural stain – color and isolate specific parts
of bacteria e.g. capsule, flagella and endospores
Types of dyes
Acidic – used to stain basic
(negatively charged) cell components
Basic – used to stain acidic cell
(positively charged) components
Structural features of bacteria
Nucleiod region &
plasmids
Cell Wall
Glycocalyx (slime &
capsule)
Flagella
Pili or Fimbriae
Endospore
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Bacterium have only about onethousandth as much DNA as a human
Its chromosome is located in the
nucleoid region
Extrochromosomal DNA – plasmids
Antibiotic resistance genes
metabolism of unusual nutrients
can be transferred between bacteria
Bacterial Cell Wall Structure
Gram stain differentiates bacteria into Gram-positive and
Gram-negative groups. The two groups differ in the
organization of the structures outside the plasma membrane
but below the capsule (see Table 4-5)
Mycobacterium species have special lipids in the cell wall and are
often identified with acid-fast stain
Gram stain
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Comparison of Gram +ve & Gram –ve bacteria
Gram +ve
Gram -ve
Gram stain reaction
Blue to purple
Pink to red
Peptidoglycan layer in
cell wall
Thick
Thin
Teichoic acid in cell wall Present
Absent
Lipopolysaccharrides
Absent
(outer membrane) in cell
wall
Present
Pathogenicity
Less
More deadly
Antibiotic susceptibility
More
Less
Many bacteria are motile
Ability to “swim” using
flagellum/flagella
Some species can move at
speeds exceeding 50
µm/sec, about 100 times
their body length per
second
Most spiral-shaped or
bacilli are motile; cocci are
non-motile
Capable of taxis (movement
towards or away from
stimuli)
Many prokaryotes secrete another sticky
protective layer
Capsule (a.k.a slime layer, glycocalyx)
glue together the cells that live as colonies
Increase adherences to surface (e.g. teeth) biofilm
May protect against host defense
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More cell surface appendages
Fimbriae allow pathogenic
bacteria to stick to host
mucus membrane
Sex pili are used in
conjugation between two
bacteria (bacterial “sex”)
Unique Bacteria: Rickettsia,
Chlamydia & Mycoplasma
Gram-negative bacteria
Rickettsia
Chlamydia
Obligate intracellular pathogens (must live within a
host)
Transmitted by arthropods vectors
Obligate intracellular pathogens
Transmitted by direct contact
Mycoplasma
Smallest microbe
Lack cell wall pleomorphic
Resistant to certain antibiotics
Unique bacteria: Photosynthetic bacteria
Capable of using light as energy source
Purple bacteria, green bacteria &
cyanobacteria
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Domain Archaea
Prokaryotic cells
Have different cell wall structure
than bacteria
Live in extreme environments
Bacterial growth (p.200-2, 207-8)
Growth in number of cells
Multiply by binary fission
As a bacterium grow to its optimal size
(double cell constituents & genetic
material), a new cell wall is synthesized in
the middle cell divided into 2 halves
Generation time (g) – time it takes for one
cell to become two cells by binary fission
(range from 20 min to 24 hr)
If you inoculate a broth with 1 bacterium
(g=30min). After 12 hours, as it divides,
you’ll have 2 24 =16777216 bacteria!
If you place 1 bacterium on an agar plate,
12 hr later, you have a mount of 16777216
cells colony
www.cellsalive.com
Bacterial (population) Growth Curve
Lag phase – absorb nutrients & synthesize enzymes, genetic
material; cell number DO NOT increase
Log phase – cell number doubles; period of maximum division;
generation time is determined from this phase
Stationary phase – nutrients depleted; growth slows down and
start dying; has the most population density
Death phase – bacteria die at a rapid rate; some survive (may
form spores)
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Bacterial survival in nature is “Feast or
Famine”
mostly in stationary or death phase
Endospore formation (sporulation) for some
species (Bacillus sp. & Clostridium sp.)
When nutrients become available, resume
growth (germination)
Endospores
resistant to heat, cold, radiation, desiccation, and disinfectants
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