Bacterial morphology in detail

1. Title and Content Layout with List

2. What is a Bacterium ?
Bacterium (pleural : Bacteria )constitute a
large domain of prokaryotic microorganisms (that lack membrane
bound organelles.)
Typically a few micrometres in length, bacteria have a number of
shapes, ranging from spheres to rods and spirals.
 Bacteria were among the first life forms to appear on Earth, and
are present in most of its habitats.
Bacteria inhabit soil, water, acidic hot springs, radioactive
waste, and the deep portions of Earth's crust.
Bacteria also live in symbiotic and parasitic relationships with
plants and animals.

3. Size Of Bacteria
• Bacterial cells are about one-tenth the size
of eukaryotic cells and are typically 0.5–
5.0 micrometres in length.
• However, a few species are visible to the
unaided eye—for example, Thiomargarita
namibiensis is up to half a millimetre long
and Epulopiscium fishelsoni reaches 0.7 mm.
• Among the smallest bacteria are members
of the genus Mycoplasma, which measure
only 0.3 micrometres, as small as the
largest viruses.
• Some bacteria may be even smaller, but
these ultramicrobacteria are not well-
studied.

4. Bacterial Cell
• Prokaryotes
* No true nucleus
* No oraganelles
• Divide by binary fission

5. Morphology of Bacterial Cell
• Essential Components (that
are essential for growth and
metabolism of bacteria)
• CellWall (Outer to cell
membrane)
• Plasma Membrane
• Cytoplasm :
• Ribosomes
• Mesosomes
• Nucleoid
• Periplasm
• Non-Essential Components
(that are not essential for
growth and metabolism of
bacteria)
• Capsule (Outer to cell wall)
• Pilus or fimriae
• Flagellum
• Spore
• Plasmid
• Granules
• Glycocalyx (slime layer)

6. Cell envelope
•It is a descriptive term for the several layers that envelope
or enclose the protoplasm of a bacterial cell.
•It includes from inner to outer : A Plasma membrane , a
Cell wall.
•And in case of gram negative bacteria ,An Outer
Membrane present external to the cell wall is also
included.
•Most of the bacterial cell envelopes fall into two types:
1- a gram-positive type
2- a gram-negative type

7. Cell capsule/Capsid :
•Some bacteria have a present outside the cell
envelope
•Capsule is found in both gram negative and
gram positive bacteria but is found most
commonly among gram negative bacteria
•It is a well organized layer and cannot be easily
washed off
•Can be the cause of various diseases
Slime layer/ Glycocalyx
When an amorphous viscid secretion that
makes up the capsule diffuses into the
surrounding medium as a loose undemarcated
secretion it is called as a slime layer.

8. Contd.
• Functions :
• Both capsule and slime are there for protection and
adhesion
• Capsule-Virulence factor (enhances the ability of
bacteria to cause disease)
• Capsule- prevents phagocytosis (and in capsulated
bacteria in order for the phagocytosis to occur , a
capsule specific antibody is needed)
• Capsule also protects the bacteria from desiccation
because of its water content
• They also protect the bacteria from bacterial viruses
and materials that are toxic to bacteria

9. Cell wall
GRAM-POSITIVE BACTERIA
• Peptidoglycan layer- thicker
multilayered
• Fibers of teichoic acid that
protrude outside peptidoglycan
• No complex OUTER LAYER
• periplasmic space is less small
• No endotoxin
GRAM-NEGATIVE BACTERIA
• Less thicker
• Do not have teichoic acids
• Complex outer layer of LPS , LP
and phospholipid
• Periplasmic space bigger than
g+ive is present between outer
membrane and cytoplasmic
membrane
• Endotoxin (LPS)
Outer to cell membrane , composed of peptidoglycan
Present in all except Mycoplasma
Structure , composition and thickness different in G+ive and G-ive Bacteria

10. HOW THE CELL WALL LOOKS LIKE IN
G+ive G-ive

14. Cell membrane
• Inner to cell wall
• Similar in microscopic appearance to eukaryotic cell
• Generally Lacks sterols (unlike eukaryotes)
• Exception is Mycoplasma ( its cell membrane has sterol )
Cytoplasm
2 distinct areas : 1-Amorphous matix having ribosomes, nutrient
granules, metabolites, plasmid
2-An inner , nucleoid region composed of DNA

15. Ribosomes
• Protein synthesis
• Different from eukaryotic ribosomes in size
• Size : 70S ( 50 S , 30S Subunits )
• Difference between Ribosomal RNA and Proteins present in bacterial
ribosomes and eukaryotic ribosomes is the basis of action of certain
antibiotics. (inhibit bacterial protein synthesis only and not human protein
synthesis)
Granules
• Storage area for nutrients
• Stain characteristically with dyes
• Corynebacterium diphteriae has votulin (a metachromatic granule) stains
red with methylene blue instead of blue

16. Nucleoid
• The area of cytoplasm in which DNA is located
• Single, circular molecule of DNA
• 2000 genes
• No nuclear membrane , no nucleolus , no mitotic spindle , no histones
• Bacterial DNA has no introns
Plasmid
• Extra chromosomal, double stranded , circular DNA molecules, capable of self
replication.
• In both g-ive and g+ive bacteria
• Several types of plasmid exist in one bacterial cell : 1-Transmissible 2- Non-
transmissible

17. Contd.
• Transmissible Plasmids
Can be transferred from cell to cell by conjugation
They are large
Have genes for synthesis of sex pilus and for the enzymes required for transfer.
1-3 copies are present per cell.
• NonTransmissible Plasmids
Cannot be transferred from cell to cell
They are small
They donot contain transfer genes
10-20 copies per cell

18. Genes carried by plasmid
• Antibiotic resistance – mediated by enzymes like Beta Lactamases of S.aureus,
E.coli
• Exotoxin – such as enterotoxin of E.coli, AnthraxToxin of Bacillus anthracis
• Pili (Fimbriae) – mediate adherence of bacteria to epithelial cells
• Resistance to heavy metalssuch as Mercury, Silver by Reductase enzyme
• Resistance to UV light by DNA repair enzymes
• Bacteriocins – products of bacteria that are lethal for other bacteria ( either
degradation of bacterial cell membrane by forming pores in it or degradation of
bacterial DNA by DNAse
• Nitrogen fixing enzymes in Rhizobium, antibiotics produced by streptomyces, a
variety of degradative enzymes by Pseudomonas capable of cleaning up
environmental hazards such as spills and toxic chemical waste sites.

19. Flagella
• Long whip like appendages
• Move bacteria towards nutrients and other attractants (Chemotaxis)
• Composed of many subunits of a single protein , flagellin arranged in several intertwined
chains.
• Energy for the movement provided by ATP.
• On the basis of number and location of flagella bacteria are categorized as :

20. Pili (Fimbriae)
• Hair like filaments extend from the cell surface
• Shorter and straighter
• Composed of subunits of pilin
• Found mainly on G-ive bacteria
• Mediate attachment of bacteria to specific receptors on human cell
surface (necessary step for initiation of infection)
• A specialized kind of pilus : Sex Pilus forms attachment between
donor and recipient bacteria during conjugation

22. Bacterial Spores
• Highly resistant structures formed in response to adverse conditions by two genera
of medically important G+ive Rods : the genus Bacillus which includes the agent of
anthrax , and the genus Clostridium which includes agents of tetanus and botulism
• Spore formation occurs when nutrients such as sources of carbon and nitrogen are
depleted
• Spore forms inside the cell and contains bacterial DNA , a small amount of
cytoplasm, cell membrane , peptidoglycan , a little water , most importantly a thick
keratin coat .
• Keratin coat is responsible for remarkable resistance of spore to heat , dehydration ,
radiation , chemicals
• Resistance maybe mediated by dipicolinic acid ,a calcium ion chelator found in
spores
• No metabolic activity , can remain dormant for years .

24. Types of bacteria based on their shape