Major groups of Microorganisms

Major groups of microorganisms are broadly classified into bacteria, fungi, protozoa, algae and virus which are diverse in nature. Microorganisms can define as the small living creatures that are sometimes not visible to the naked eye. Therefore, its study becomes important for us to know more about microorganisms like its cell structure, cell components, genome, distribution, effects etc.

Microorganisms are beneficial while some are deleterious.  All the major groups of microorganisms show a practical significance in many fields like medical, research, industrial, environmental biology etc.

Content: Major groups of Microorganisms

  1. Groups of Microorganisms
  2. Comparison Chart
  3. Biological Significance

Groups of Microorganisms

There are five major groups of microorganisms which include:

  1. Bacteria
  2. Fungi
  3. Protozoa
  4. Algae
  5. Viruses


Cell properties: Bacteria is a prokaryotic cell (having a primitive nucleus) and unicellular.
Size: It ranges from 0.2-100 µm
Shape: It is variable in shape and is broadly classify into:

  • Bacillus
  • Coccus
  • Vibrio
  • Spirillum
    different forms of bacteria

It is simply “Pleomorphic” in nature.
Distribution: Worldwide
Habitat: Soil, water, earth crust, dead organic matter, hot springs etc.
Movement: For the movement of bacteria, it has whip-like structure refers as “Flagella”.
Nucleus: True nucleus absent.
Genetic material: The genetic material of bacteria can be either DNA or RNA.

  • On the basis of cell wall characteristics: Bacteria classifies into Gram-positive and Gram-negative.
  • On the basis of cell shape: Bacillus, Coccus, Vibrio and Spirillum.

Resistance: Some strains of the bacteria are resistant to adverse conditions like high Ph, temperature, high salt concentration and many antibiotics etc.
Nutrition type: Heterotrophic or autotrophic
Chlorophyll: Present in photosynthetic bacteria like purple and green bacteria.
Reproduction: Bacteria reproduce by the both asexual and sexual method:

  • Asexual methods include budding, fragmentation and most commonly binary fission.
  • Sexual methods include transformation, transduction and conjugation.

Absorption: Bacteria absorb nutrients with the help of flagella that is used to trap the food or other organisms.
Nature: Some bacteria are symbiotic and parasitic in nature.
Morphology: Simple
Carotenoids: Wide variety of carotenoids are present in a class of bacteria.
On the basis of oxygen requirement bacteria, can be aerobic, anaerobic and facultative anaerobes.


Cell properties: Fungi are eukaryotic and can be multicellular or unicellular.
Size: The size of moulds ranges from 2.0-10.0 µm and the size of yeast ranges from 5.0-10.0 µm.
Shape: A fungus has two distinct morphological shapes: In the vegetative stage, it consists of a hyphal network and in the reproductive stage, it consists of fruiting bodies emerges out of hyphae.
Distribution: Worldwide
Habitat: Deserts, deep-sea sediments, soil, dead organic matter etc.
Movement: In fungi, there is no apparatus for locomotion, there is only the movement of spores through air or wind.
Nucleus: True nucleus present.
Genetic material: In fungi, either DNA or RNA is present.
Types: On the basis of cell type: fungi are broadly classified into yeast and moulds.
different forms of fungi

Resistance: fungal spores are also resistant to many antibiotics, chemicals, ph, temperature etc.
Nutrition type: Most of them are heterotrophic.
Chlorophyll: Present
Reproduction: Fungi reproduce by vegetative, asexual and sexual methods.

  • Vegetative methods include binary fission and budding.
  • Asexual reproduction include hyphae fragmentation, chlamydospore formation, transverse cell division etc.
  • Sexual reproduction include gamete fusion, gametangial contact, gametangial coapulation, spermatization and somatogamy.

Absorption: Fungi absorbs food and nutrients by hyphae.
Nature: Fungi are also symbiotic and parasitic in nature.
Morphology: Complex
Carotenoids: Present
Most of the fungi grow in the presence of oxygen i.e. aerobic.

fungal cell


Cell properties: These are eukaryotic and multicellular.
Size: It ranges from 2.0-200  µm
Shape: Protozoa are variable in shape.
Distribution: Cosmopolitan
Habitat: Soil, plant, marine water, freshwater etc.
Movement: Protozoa move through the help of cilia and flagella.
Nucleus: Consist of a vesicular nucleus.
Genetic material: DNA
Types: There are four types of protozoa: Flagellates, Ciliates, Amoeboid and Sporozoans
Resistance: Some parasitic protozoans are drug resistance.
Nutrition type: Most of the protozoans are heterotrophic and few are autotrophic.
Chlorophyll: Few protozoans contain green chlorophyll pigment.
Reproduction: Protozoans reproduce by budding, binary fission, schizogony, multiple fission etc.
Absorption: Protozoa uptake food by cytosome present on the cell wall with the help of flagella and pseudopodia.
Nature: Protozoans are Paraphyletic in nature.
Morphology: Complex
Carotenoids: Present
Most of the protozoans are aerobic.
protozoan cell


Cell properties: Algae are eukaryotic and can be unicellular or multicellular or colonial.
Size: It ranges from 1.0 µm to several feet.
Shape: Algae exist in variable shapes or irregular structure.
Distribution: Worldwide
Habitat: Freshwater, marine water, brackish water, moist soil etc.
Movement: They move through their flagella.
Nucleus: True nucleus present.
Genetic material: DNA
Types: Euglenoids, Golden brown algae, Fire algae, Green algae, Red algae, brown algae and Yellow-green algae.
Resistance: Some are resistant to radiation.
Nutrition type: Autotrophic
Chlorophyll: Present
Reproduction: Algae reproduce by vegetative, asexual and sexual reproduction.

  • A vegetative method includes budding, binary fission, through hormogonia etc.
  • An asexual method includes reproduction through spores like zoospores, aplanospores, tetraspores, akinetes, exospores, endospores.
  • A sexual method includes gamete fusion such as autogamy, hologamy, isogamy, anisogamy and oogamy.

Absorption: Algae prepare food by their own in the presence of sunlight and chlorophyll i.e. through photosynthesis.
Nature: Heterotrophic and parasitic in nature.
Morphology: Complex
Carotenoids: Present
Algae can be aerobic or anaerobic.

algal cell


Cell properties: Virus are prokaryotic and acellular microorganisms.
Size: It ranges from 0.015-0.2 µm
Shape: Its shape is generally icosahedral and few are spherical, helical and complex.

different forms of virus

Distribution: Ubiquitous
Habitat: These are mainly living inside the host.
Movement: They move into the host cell by recognition of receptor site through tail pin and tail fibres by various methods like endocytosis and exocytosis.
Nucleus: Absent
Genetic material: In viruses either DNA or RNA is present.
Types: Viruses are broadly classified into a plant, animal and human virus on the basis of their effect.
Resistance: These are resistant to many drugs or antibiotics.
Nutrition Type: Parasitic
Chlorophyll: Absent
Reproduction: Viruses replicate inside the host via lytic and lysogenic replication cycle.
Absorption: Its absorption is through tail fibres.
Nature: Viruses only shares a parasitic relationship with other organisms.
Morphology: Simple
Carotenoids: Absent

Comparison Chart of five major groups of microorganisms

Cell characteristicsBacteriaFungiProtozoaAlgaeVirus
Cell typeProkaryoticEukaryoticEukaryoticEukaryoticProkaryotic
Cell wallPresentPresentPresentPresentAbsent
Cell membranePresentPresentPresentPresentAbsent
Nuclear membraneAbsentPresentPresentPresentAbsent
Endoplasmic reticulumAbsentPresentPresentAbsentAbsent
Golgi bodyAbsentPresentPresentPresentAbsent
Food vacuolePresentPresentPresentPresentPresent

Biological Significance of five major groups of microorganisms

Some microorganisms are beneficial and some are detrimental so on the basis of this, they play a significant role in an ecosystem:

The significance of bacteria: Bacteria can be pathogenic as well as non-pathogenic. Pathogenic microorganisms cause many diseases in both animals and human. Some play an important role in a symbiotic association, nitrogen fixation, nutrients recycling. Some bacteria cause food spoilage while some are used in the food industry.

The significance of fungi: Fungi are also pathogenic and non-pathogenic. Pathogenic fungi cause diseases in all plants, animals and human. biologically important fungi play an important role in food industries for the production of alcoholic beverages, bread and other food supplements, medicines etc. Others play a vital role in the decomposition of organic matter, symbiotic association with algae etc.

The significance of protozoa: Most of the protozoans doesn’t cause diseases but some cause severe diseases. They play a significant role where it acts as “Producer” or food material for other microorganisms. It shows a symbiotic relationship with the associative organisms and also acts as an organic pollution indicator.

The significance of algae: Algae produce toxic substances that cause several infections. Others play a significant role in the preparation of microbiological media, pharmaceuticals preparations and biofertilizers. Algae also act as a pollution indicator and also being used as a food supplement.

The significance of virus: Virus is the type of microorganisms which are only pathogenic and causes severe diseases in plants, animals and humans, therefore these are important in the field of medical biology.

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