General characteristics of bacteria:
- Lack rigid cell wall.
- Lacks nuclear membrane so distinct nucleus and nucleolus absent.
- Most of the bacteria lack chlorophyll called heterotrophic, few bacteria poses chlorophyll called as autotrophic.
- Genetic material represented by histone free DNA.
- Commonly reproduce vegetatively by fission.
- Variations in the genetic character are due to genetic recombination by conjugation, transformation and transduction.
Shape and Size:
a) Spherical: Bacteria shaped like a ball are called cocci, and a single bacterium is a coccus. Examples include the streptococcus group, responsible for “strep throat.”
b) Rod-shaped: These are known as bacilli (singular bacillus). Some rod-shaped bacteria are curved. These are known as vibrio. Examples of rod-shaped bacteria include Bacillus anthracis (B. anthracis), or anthrax.
c) Spiral: These are known as spirilla (singular spirillus). If their coil is very tight they are known as spirochetes. Leptospirosis, Lyme disease, and syphilis are caused by bacteria of this shape.
- Average size: 0.5 to 1 x 2 to 5 micrometer.
- Longest: Bacillus butschlii is 80 micrometer.
- Shortest : Dialister pneumosintes is 0.15 – 0.31 micrometer.
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