Important Plant Pathogenic Organisms Bacteria
It is the study of size, shape, structure, and arrangement of cells.
a) Size of Bacteria:
Bacteria are very small or minute, as single drop of water may contains about 50 billions of bacteria are usually measured in micrometer (µm) which is equivalent to 1/1000 mm.
1. Size may varies depending upon the species. Size generally ranges from 1 to 10 microns.
2. Most of the bacterial cells 0.5 to 1 µm in width or diameter.
3. Cylindrical or rod (Baclli) 2-3 µm length.
4. Spiral or helical (Spirlli) – 0.75 -1.25 µm.
b) Shape in Bacteria:
The shapes of bacterial cells are
Spherical or Ellipsoidal or Oval – Cocci
Cylindrical or rod- Bacilli
Spiral or Helical – Spirilli
Some species have variety of shapes and thus termed as pleomorphic. E.g. Arthrobacter.
c) Arrangement of Bacterial Cells:
Bacterial cells are arranged in a characteristic manner of the particular species. The typical pattern of cell arrangement in different bacteria is an important characteristics used in identification of bacteria.
d) Cell grouping or Arrangement in Cocci:
Single spherical bacterial cell.
A coccus divides into two plane and cells remains in pairs.
A coccus is arranged in a long chain e.g. Streptococcus sp.
A coccus divides in two plans, second division at a right angle to the first plane of division and forms a square of four cells. E.g. Tetracoccus sp
A cube of eight coccus cell is formed by three divisions in alternate planes at right angle to each other. A cube of eight cells is known as Sarcina.
A coccus cells divides in three planes in irregular pattern like cluster of cells or bunch of grapes. E.g. Staphylococcus albus
The short comma shaped cells are called as Vibrio. Short tightly coined rods are called spirillum. Vey long cell with several cuvves and twiste are called “Spirochete”.
e) Cell Grouping or Arrangement in Bacilli:
Single rod shaped bacterial cell. E.g. Monobacillus.
Bacilli are arranged in a pair of two cells. E.g. Bacillus subtilis.
Cells are arranged in a chain. E.g. Lactobacillus bukgaricus.
Group of cells lined side by side like matchsticks in a match box called as palisade arrangement.
f) Flagellar Arrangement in Bacteria:
All types of bacteria do not have a flagella they are mostly present in Bacilli and Spirilli and rarely in cocci.
A cell without flagella.
Single polar flagellum at one end.
A cell with a single polar flagellum at both the ends. E.g Spirillim.
A cell having tuft or bunch of flagella at both the ends. E.g. Coli.
A cell having a pair of flagella at one end.
Arrangement in Spirilli:
The Spirilli are predominantly unattached however they differ in frequency of turns and overall length. They are grouped in three types as:
a) Short tightly coiled rod called spitillium
b) Short incomplete spirals called as comma or vibrios.
c) They are long twisted with several curves calls “Spirochete”.