This document discusses bacterial cell size, shape, and arrangement. It begins by noting that bacterial cells vary in size from 600 micrometers to the smallest at 200 nanometers. The largest is Bacillus megaterium and the smallest is Mycoplasma. Bacterial cell shapes include cocci (spherical), bacilli (rod-shaped), spiral, and other irregular shapes. Cocci can be arranged as single cells, diplococci, staphylococci, or streptococci. Bacilli include single cells, diplobacilli, chains, and clusters. Other arrangements include spirilla, spirochetes, and pleomorphic or branching shapes. Bacterial cell structure is related to their shape and

1. CELL SIZE, SHAPE AND ARRANGEMENT
PRESENTED BY
AVIJIT BANERJEE
1st SEMISTER (2017) B.Sc Hons.
DEPERTMENT OF MICROBIOLOGY
MICHAEL MADHUSUDAN MEMORIAL COLLEGE

2. Introduction - Bacterial cells are prokaryotic cells having very small size and
different types of shapes. More over these cells are arranged on different planes
to form various arrangement . But their cellular structure is simpler than other
multicelluar eukaryots. Due to presence of a rigid cell wall outside the cell,
bacterial cells has a definite shape as well as size and structures.
CELL SIZE, SHAPE AND ARRANGEMENT

3. BACTERIAL CELL SIZE
Measurement of bacterial cell
Scale
1m=1000mm
1mm=1000µm
1µm= 1000nm
Now, bacterial cells are measured by micrometer and the cell organelle and
their thickness are measured by nanometer .

4. Largest bacterial cell- The largest
bacterial cell is Bacillus megaterium .
a. It may be visible through naked eye.
b. Its length is about 600µm.
c. Its diameter is about 80µm.
Bacterial cells are observed in various sizes.
Smallest bacterial cell- In early
days it was found that Streptococcus
pneumoniae was the smallest
bacterial cell.
Fig-Bacillus megaterium
Fig-Streptococcus pneumoniae

5. Interisting features of
Mycoplasma sp.
a. It lacks cell wall.
b. Outer membrane is
cytoplasmic membrane.
c. As the cell wall is absent, they
are unaffected by many
common antibiotics such as
penicillin or other β-lactam
antibiotics that target cell wall
synthesis.
d. They can be parasitic or
saprotrophic.
But now a days, it has been found that Mycoplasma sp is the smallest bacterial
cell.
Parasitic form of Mycoplasma - Mycoplasma pneumoniae.
Fig-Mycoplasma sp

6. Some other bacteria with different size
1. Escherichia coli- Length- 3µm
Diameter- 1µm.
Interesting features
a. These are the most well known and diverse
species of microbs in the world.
b. They are mostly harmless and found in Fig-Escherichia coli
gastrointestinal tracts of humans and other vertebrates.
c. They can synthesis vitamin K and vitamin B complex .
d. They also help in food digestion and absorption.
2. Haemophilus influenzae- size-0.25x1.2µm.
Interesting features
a. The most common type of disease caused by
Haemophilus influenzae type b(Hib) are
pneumonia, meningitis,bactermia, epiglottitis etc.
b. They are gram negative, highly pathogenic to human.
c. Non-typeable Haemophilus influenzae cause
common ear infection in children and bronchitis in adults etc.
Fig-Haemophilus influenz

7. BACTERIAL CELL SHAPE AND ARRANGEMENT
When viewed under light microscope, the most bacteria apper in various types-
They are
1. Cocci -Bacteria having spherical or oval
in shape are called cocci.
a. Monococcus- A single cocci cell arranged
in a single plane.
Ex- Thiocapsa roscopersicina
b. Diplococci – Two cocci cells arranged in a
single plane.
Ex- Neisseria sp.
Fig- Neisseria sp.
c. Tetracoccus- Four cocci cells arranged in
two different planes.
Ex- Merisopedia sp.
Fig -Thiocapsa roscopersicina
Fig- Merisopedia sp.

8. d. Sarcinal arrangement- Eight cocci cells arrange
in three different planes.
Ex-Sarcina lutea.
e. staphylococcus-cluster of bacterial cells arranged
in different plane.
Ex-Staphylococcus aureus
f. Streptococcus- Many bacterial cocci cells are
arranged in a linear chain.
Ex- Streptococcus sp.
2. Bacilli- The bacteria with rod or elongated
cylindrical shape are called bacilli.
a. Monobacilli- The bacteria with one bacillus
cell arranged in a single plane.
Ex- Desulfuromonas acetoxidans.
b. Diplobacili- The bacteria with two bacilli
cells arranged in a single plane.
Ex-Klebsiella pneumoniae.
Fig-Sarcina lutea.
Fig-Staphylococcus aureus
Fig- Streptococcus sp.
Fig- Desulfuromonas acetoxidans.
Fig-Klebsiella pneumoniae.

9. c. Bacilli in cluster- Large number of bacilli cells arranged
in different plane.
Ex- Streptobacilli sp.
d. Bacilli in chain- Many bacilli cells are arranged in a
linear chain.
Ex- Bacillus anthracis.
e. Bacilli in cruciform arrangement- Some bacilli cells are
arranged in a cruciform.
Ex- Corynebacterium sp.
f.Bacilli ina rosette arrangement-Ex- caulobacter sp.
3.Spiral shape-These bacteria are carved, rod or comma
shaped with vibriatory motility.
Ex-Vibrio cholerae.
Fig- Streptobacilli sp.
Fig- Bacillus anthracis.
Fig- Corynebacterium sp.
Fig- caulobacter sp.
Fig-Vibrio cholerae.

10. 3. Other shape
a.Star shape. Ex- Stella sp. are star shape bacteria.
d.Coccobacilli-Some bacteria are spherical or slightly
elongated known as coccobacilli.
Ex-Streptobacillus moniliformis.
e. Spirilla-Bacteria with a rigid twisted or helical spiral
form are known as spirillia.
Ex- Rhodospirillum rubrum.
f. Spirochetes - Tightly coiled bacteria with corkscrew
shaped, helical, flexible having axial filament.
Ex- Spirochetes stenostrepta.
Polymorphism- Some bacteria may exhibit variation in there shape and size
individually, Known as Polymorphism. Ex- Gonococcus sp. , Bacillus sp.
Rhizobium sp show swollen forms in ageing cultures having high salt
concentration.
Fig-Streptobacillus moniliformis.
Fig- Rhodospirillum rubrum.
Fig-Spirochetes stenostrepta.
Fig-Stella sp

11. b. Rectangular bacteria-Haloarcula sp. a genus of
halophilic archaea, are rectungular in shape.
c. Actinomycetes- Branched, filamentous
bacteria resembling to the radiating rays
seen in tissue lesions
Ex- Nocardia sp.
h. Mycoplasma- Lacking cell wall, round or
oval, small and pleomorphic in nature.
Ex- Mycoplasma genitalium.
e. Appendaged bacteria – posses extension
of their cells as long tubes or stalks.
Ex-Rhodospirillum rubrum.
Fig-Haloarcula sp
Fig-Nocardia sp
Fig- Mycoplasma genitalium.
Fig- Rhodospirillum rubrum.

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