Bacteria – Characteristics of Bacteria
The prokaryotic (primitive cell type) kingdom includes simple, small, microscopic organisms called the bacteria. These are the most abundant and ubiquitous (omnipresent) organisms residing on mother earth. Bacteria are found everywhere on our mother planet including in soil, hot springs, icebergs, deep ocean beds, driest deserts, hairs or animals etc. these might be considered harmful, but are more beneficial for our existence.
General Characteristics of Bacterium
The following characteristics are common to most of the bacteria –
- Found everywhere, in all possible habitats.
- These are basically unicellular but may live in association with other cells forming colonies.
- The bacterial cell is delineated by a rigid cell wall. The cell wall is made of lipopolysaccharides and murein 9peptidoglycan).
- Bacteria is devoid of any nucleus, nucleolus or nuclear membrane. The genetic materials are localized within a discrete region called the nucleoid. The nucleoid is not separated from the cytoplasm.
- The DNA is mostly circular in nature and are not associated histone proteins.
- None of the membrane bound cell organelle are present like the golgi bodies, endoplasmic reticulum, mitochondria, chloroplast etc. this makes the interior of the cell morphologically simple compared to other eukaryotic (modern) cell types.
- The ribosomes are found scattered within the cytoplasm and are mostly of 70s type.
- A bacterium may possess more than one flagella (locomotive organ).
Identification of bacteria
The bacterial cells are stained by simple staining methods to study their size, shape and arrangement.
Gram’s Staining –
- Based on their cell wall types, they are categorized into Gram-positive and Gram-negative bacteria.
- This staining technique was developed by Hans Christian Gram, a Danish physician in the year 1883.
- This is the most widely used method of bacterial staining and classification.
Characteristics of a Gram-positive bacterium are given below –
- The cell is made of two layers; the cell membrane and the cell wall (thick layer of peptidoglycan). Thus, making the cell wall thick.
- The amount of lipid is less in the cell wall, which retains the stain back in the cell.
Characteristics of a Gram-negative bacterium are given below –
- The cell envelop is thin but, made of three layers; the cell wall, a thin layer of peptidoglycan) and cell membrane.
- Large quantities of lipids are present in the cell, which dissolves in ethanol and washing away the stain.
Acid fast staining –
Some bacteria need a little harsh methods of treatment for staining. This staining method is based on the lipid content of the cell.