Classification of microorganisms | bacteria, archaea, protozoa, algae, fungi, viruses

 

Classification of microorganisms | bacteria, archaea, protozoa, algae, fungi, viruses

                     Classification of microorganisms

• Ø  bacteria
• Ø  archaea
• Ø  protozoa
• Ø  algae
• Ø  fungi
• Ø  viruses
• Ø  multicellular animal parasites

1: Bacteria

Bacteria are unicellular organisms lacking a nucleus.

They have four major shapes:

• v  bacillus (rod shape)
• v  coccus (spherical shape)
• v  spirilla (spiral shape)
• v  vibrio (curved shape)

Cell Wall

Most have a peptidoglycan cell wall.

Binary fission

Becteria divide by binary fission.

Classification of Becteria

The major feature used in the classification of bacteria is difference in their cell wall structure.

They can be classified as either Gram-positive or Gram-negative by using the Gram staining.

They can be further categorized based on their response to gaseous oxygen into following three groups:

Aerobic bacteria

They live in the presence of oxygen

Anaerobic bacteria

They live without oxygen

Facultative anaerobes

They can live in both environments

 Based on the way they obtain energy; bacteria are divided as heterotrophs or autotrophs.

Autotrophs

They produce their own food by utilizing the energy of sunlight or chemical reactions.

Heterotrophs

By consuming other organisms, they obtain their energy.

2: Fungi

Fungi are non-motile and heterotrophs.

The defining characteristic of fungi is their mode of obtaining food

• ·         Extracellular digestion
• ·         Absorption

Most fungi are decomposers, live on decaying organisms. Some are parasites.

3: Algae

Also known as cyanobacteria or blue-green algae.

They are unicellular or multicellular eukaryotes that obtain food by photosynthesis.

Habitat

They live in water, damp soil, and rocks.

4: Viruses

• They are noncellular entities.
• Composed of a nucleic acid core (DNA or RNA) and protein coat.
• They are not considered living organisms.
• Viruses cannot reproduce without the host cell
• They cannot metabolize on their own.

5: Archaea

According to their habitat, all Archaeans can be categorized into the following groups:

v  methanogens

They are methane-producing organisms

v  halophiles

They live in salty environments

v  Thermophiles

They live at extremely hot temperatures),

v  Psychrophiles

Cold-temperature Archaeans

Archaeans utilize different energy sources e.g., hydrogen gas, carbon dioxide, and Sulphur.

Some of them utilize sunlight to make energy, but their way of making energy is different from that of plant.

They absorb sunlight using bacteriorhodopsin (membrane pigment).