Classification of Microorganisms based on Major Groups

Introduction

Microorganisms are classified into different groups based on their cell structure, mode of nutrition, reproduction, and ecological role. The major groups include Bacteria, Archaea, Fungi, Protozoa, Algae, and Viruses. Each of these groups has unique characteristics that define their role in nature, industry, and human health.

[1] Bacteria (Eubacteria – True Bacteria) :

 

General Characteristics:

• Unicellular prokaryotic organisms.
• Lack a membrane-bound nucleus and organelles.
• Have a peptidoglycan cell wall (except Mycoplasma).
• Reproduce through binary fission.
• Can be autotrophic (photosynthetic or chemosynthetic) or heterotrophic (saprophytic or parasitic).
• Some bacteria form endospores for survival in harsh conditions.

 

[2] Archaea (Ancient Bacteria – Extremophiles) :

 

General Characteristics:

• Unicellular prokaryotic organisms, but different from bacteria.
• Lack peptidoglycan in the cell wall; instead, have pseudopeptidoglycan.
• Found in extreme environments like hot springs, deep-sea vents, and salt lakes.
• Use unique metabolic pathways such as methanogenesis.

 

[3] Fungi (Eukaryotic Heterotrophs) :

 

General Characteristics:

• Eukaryotic, multicellular, or unicellular organisms.
• Have chitinous cell walls (instead of peptidoglycan).
• Absorb nutrients from organic material.
• Reproduce asexually (spores, budding, fragmentation) or sexually (spore formation).
• Some fungi cause diseases (pathogenic fungi), while others are used in food production (yeast in bread, fermentation).

 

[4] Protozoa (Unicellular Animal-Like Microorganisms) :

 

General Characteristics:

• Eukaryotic, unicellular, heterotrophic microorganisms.
• Lack a cell wall but may have a pellicle.
• Move using cilia, flagella, or pseudopodia.
• Reproduce asexually (binary fission, budding) or sexually (conjugation).
• Some protozoa are parasitic and cause diseases like malaria, amoebiasis.

 

[5] Algae (Plant-Like Protists – Photosynthetic Microorganisms) :

 

General Characteristics:

• Eukaryotic, autotrophic, unicellular or multicellular.
• Have cellulose cell walls and perform photosynthesis.
• Found in freshwater, marine environments, or on moist surfaces.

 

[6] Viruses (Acellular Infectious Agents) :

 

General Characteristics:

• Non-living outside a host, living inside a host.
• Made of nucleic acid (DNA or RNA) and protein coat (capsid).
• Require a host cell for reproduction.
• Cause diseases in humans, plants, and animals.