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Shape

Coccus, Bacillus, Spiral, Unusual, Pleomorphic, No fixed shape

Size

0.2 to 2.0 μm in diameter and 2 to 8 μm in length

Arrangement

Cocci

- diplococci (s., diplococcus) – pairs
– streptococci – chains
– staphylococci – grape-like clusters
– tetrads – 4 cocci in a square
– sarcinae – cubic configuration of 8 cocci

Bacilli

diplobacilli and streptobacilli

Spiral

vibrio, spirillum and spirochetes

Meaning

a group of organisms
that lack a cell nucleus or any other membrane-bound organelles

Most are unicellular, but a few prokaryotes

Threadlike, locomotor appendages
extending outward from plasma membrane
and cell wall

Gram positive organisms have 2 rings, one in the cell wall and one in the cell
membrane. Gram negative organisms have 4 rings, 2 in the cell wall and 2 in
the cell membrane

Made of the protein flagellin and consists of a filament and basal region. The

Functions

– motility and swarming behavior
– attachment to surfaces
– may be virulence factors

Types of flagella

Monotrichous – one flagellum
Polar flagellum – flagellum at end of
cell
Amphitrichous – one flagellum at each
end of cell
Lophotrichous – cluster of flagella at
one or both ends
Peritrichous – spread over entire
surface of cell

Motility

Run or swim: moves in one direction for a length
of time
Tumbles: runs interrupted by periodic,
abrupt, random changes in
direction
Swarm: rapid wavelike movement

• Thick, aqueous, semitransparent and elastic.
• The major structures in the prokaryotic cytoplasm
are DNA, ribosomes and inclusions.

Also contains proteins (enzymes), carbohydrates,
lipids, inorganic ions and many low molecular
weight compounds.

Plasma membrane infoldings
– observed in many photosynthetic bacteria
– observed in many bacteria with high respiratory activity

Anammoxosome in Planctomycetes
– organelle – site of anaerobic ammonia oxidation

• Reserve deposits
• Can serve as a basis of identification

Metachromatic granules

• Large inclusion.
• Stain red with certain blue dyes such as
methylene blue.
• Collectively known as volutin (inorganic
phosphate- polyphosphate used in the
synthesis of ATP).

Corynebacterium diphtheriae.
Also found in algae, fungi, protozoa
(eukaryotic).

Polysaccharide granules

• consist of glycogen and starch.
• differentiated by using iodine:
-reddish brown indicates glycogen
granules
-blue indicates starch granules

Lipid inclusions

• storage material -polymer poly-β-
hydroxybutyric acid
• revealed by Sudan dyes (fat-soluble)
• Mycobacterium, Bacillus, Azotobacter,
Spirillum

Sulfur Granules

• Sulfur granules-serve as an energy reserve.
• Derive energy by oxidising sulfur and sulfurcontaining
compounds.
• Thiobacillus - sulfur bacteria.

Carboxysomes

• Contain the enzyme ribulose 1,5-
diphosphate carboxylase.
• Used for carbon dioxide fixation during
photosynthesis.
• Nitrifying bacteria, cyanobacteria and
thiobacilli- used carbon dioxide as sole
source of carbon.

Magnetosomes

• Iron oxide (Fe3 O4) that act like magnets.
• For downward movement until reaching
suitable attachment site.
• Function to protect the cell against hydrogen
peroxide accumulation.
• Aquaspirillum magnetotacticum (gram –ve
bacteria).

Gas vesicles

• Hallow cylinders covered by protein
• Membrane bounded
• Collectively called gas vacuole

Function: provide buoyancy for aquatic
prokaryotes- to receive sufficient amounts
of oxygen, light and nutrients

Found in photosynthetic group;
• -cynobacteria
• -proteobacteria
• -green sulfur bacteria
• -heterotropic bacteria
• -archaea- Methanogen and
halophiles

Function as the sites of protein
synthesis

• Two subunit (small subunit-30S subunit
and large subunit-50S subunit). S refer
to Svedberg unit.
• Each subunit consists of protein and
RNA called ribosomal RNA or rRNA.

Several antibiotics work by inhibiting protein
synthesis on prokaryotic ribosomes:
– Streptomycin and gentamicin attach to the 30S
subunit.
– Erythromycin and chloramphenicol attach to the
50S subunit.

Bundles of fibrils that arise at the ends of the cell
beneath the outer sheath

spiral around the cell

Present in a spirochetes group of bacteria

Used for attachment rather than for motility

Fimbriae

- can occur at the poles of the bacterial cell
- can be evenly distributed over the entire
surface of the cell
- can number anywhere from a few to several
hundred per cell

Pili

- Longer than fimbriae
- Only one or two per cell
- Pili joint bacterial cells in preparation for
the transfer of DNA from one cell to
another
- Sometimes are also called sex pili.

surrounds the cytoplasmic
membrane
not a regulatory structure like
cytoplasmic membrane
not selectively permeable

Composition and characteristics

composed of a macromolecular network called
peptidoglycan (also known as murein).

The disaccharide portion is made up of
monosaccharides called N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM).

Functions

Prevent bacterial cell from rupturing when
the water pressure inside the cell is greater
than that outside the cell
Contributes to pathogenicity
Classification
Maintains characteristic shape
provides a rigid platform (a point of anchorage)

Bacteria

Gram Positive

thick peptidoglycan layer
– peptide
amino acids
cross linked
– glycan
sugar
– 90% of the cell wall is
peptidoglycan

Periplasmic space lies between plasma membrane and cell
wall and is smaller than that of Gramnegative
bacteria

teichoic acid

Lipoteichoic acid (spans the peptidoglycan
layer and is linked to the plasma
membrane)

Wall teichoic acid (link to the peptidoglycan
layer).

Gram Negative

Consist of one or very few layers of
peptidoglycan (more susceptible to
mechanical breakage).
The peptidoglycan i s bonded to
lipoprotein.
Do not contain teichoic acids

peptidoglycan layer
– 10% of cell wall
– bonded to lipoproteins
– located between outer membrane and the
cytoplasmic membrane

periplasmic space
– contains a high concentration of degrading enzymes
– large number of transport proteins
– (20-40%) of cell volume

Archaea

Some species have cell walls consisting of
polysaccharide, glycoprotein, or protein but not
peptidoglycan
However, contain a substance similar to
peptidoglycan called pseudopeptidoglycan
(pseudomurein).

Gram Positive

Pseudomurein (in methanogenes)

Gram Negative

A layer/2 of thick protein or glycoprotein
outside plasma membrane

substances that surround cell
It is made inside the cell and excreted to the cell
surface

Functions

1.Protection from
phygocytosis
2. Attachment to various
surfaces
3. Source of nutrients
4. Protect a cell against
dehydration.

Capsules

– distinct and gelatinous
– antiphagocytic
– protect from dehydration

Slime layer

– disorganized and loosely attached

phospholipid bilayer with
proteins embedded in and attached to
the inner (intracellular) and outer
(extracellular) surfaces

Functions

1. Selectively permeable barrier 2. Synthesizes cell wall components
3. Assists in DNA replication
4. Carries on respiration
5. Captures energy as ATP

Destruction

Disinfectants – alcohols and quaternary
ammonium compounds
– Cause leakage of intracellular contents - plasmolysis: cells shrink
– lysis: cells burst

Uptake of Nutrients

Macroelements

– C, O, H, N, S, P
• found in organic molecules such as proteins, lipids,
carbohydrates, and nucleic acids
– K, Ca, Mg, and Fe
• cations and serve in variety of roles including
enzymes, biosynthesis
– required in relatively large amounts

Microelements

– Mn, Zn, Co, Mo, Ni, and Cu
– required in trace amounts
– often supplied in water or in media components
– ubiquitous in nature
– serve as enzymes and cofactors

Movement

Active Processes

Active transport

– substances are moved by
transporter proteins from low to
high concentration
– cell has to expend energy for
this to happen

Group translocation

– molecules are chemically modified
during passage across cytoplasmic
membrane
– energy is expended

Passive Processes

Simple diffusion

movement of molecules or ions from high to low
concentration until equilibrium.

Facilitated diffusion

needs a carrier proteins (transporters).

Osmosis

movement of water molecule from high to low
concentration

• Single long circular molecule of double-stranded
DNA (bacterial chromosome).
• Bacterial chromosome do not include histones and
are not surrounded by nuclear envelope.

Plasmid

• Small circular, double stranded DNA.
• Extrachromosomal genetic elements:
– not connected to bacterial
chromosome
– replicate independently of chromosomal DNA
- Do not contain genetic material
essential for growth (limited).

– resting structures formed by some bacteria for
survival during adverse environmental conditions
– germination results in leaving the dormant stage
and once again becoming a typical, multiplying cell
(vegetative cell)

genus Bacillus and Clostridium are two
common disease causing bacteria that
produce endospores as needed

• Bacillus anthracis
• Clostridium tetani
• Clostridium botulinum
• Clostridium perfringens.

Spores are very impermeable to dye.
However, they can be stained with special
dye, Malachite green

• cannot be destroyed easily, even by harsh chemicals.
• are formed internal to the bacterial cell membrane
• Highly resistant differentiated bacterial cell
• Enable the organism to endure extreme environmental
conditions
• Endospore formation leads to a highly dehydrated
structure thick walls and additional layers
• Contain essential macromolecules and a variety of
substances absent from vegetative cells