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Actinomycetes Introduction

The actinobacteria is included in the phylum of a gram-positive bacterium. These can be terrestrial or aquatic organisms. They have great economic importance. It provides a great contribution to the soil system, thus helping humans in agriculture and forests. They help in the decomposition of dead organic matter and help the plants to absorb the molecules that are present in the soil. The Actinomycetales belong to the order of actinobacteria. A member that is present in this order is called actinomycetes. These are gram-positive and anaerobic organisms where they are diverse and contain a variety of species.

What are Actinomycetes?

The actinomycetes meaning is as follows they are the unicellular organisms that belong to the Actinomycetales order and these are gram-positive bacteria. Around the world, these can be found in a wide variety of distribution in several habitats in the natural world. The word “Actinomycetes” is derived from Greek, where “atkis” means ray and “myles” means fungi. Formerly these are categorized under the group of fungi. It is found that these can share some characteristics with fungi and also capable of causing the same diseases in the eye as that of fungi. 

Along with the wide distribution they are versatile nutritionally as well and these are capable of producing various types of spores. Having these characteristics helps them to compete with other organisms that are present in the surroundings. Some members that are present in this group can cause various diseases and they are the important soil organisms that produce biologically active compounds that can be used as insecticides, and antibiotics, etc.

Actinomycetes Examples: 

  • Actinomyces meyeri

  • Actinomyces israelii

  • Streptomyces coelicolor

  • Streptomyces scabies

  • Nocardia brasiliensis

  • Nocardia asteroides

Actinomycetes Classification

Kingdom: They belong to the kingdom bacteria, thus these are unicellular organisms that have a simple cell structure. As members of this kingdom, they can be found in various habitats all over the world where some of these species are capable of causing mild to severe health disorders in human beings. Since these are Gram-positive bacteria they can contain a peptidoglycan layer in the cell wall. 

Phylum: They belong to the phylum Actinobacteria, as a member of this phylum Actinomycetes are said to be Gram-positive with having the highest content of “G + C” in the DNA structure. These are found in aquatic and terrestrial regions, they have the ability to exhibit nutritional versatility in a higher range. They even produce mycelium.

Subclass: They belong to the subclass actinobacteria, this subclass is diverse and consists of wide varieties of organisms that are present in most of the habitats. 

Order: The Actinomycetes belong to the order Actinomycetales, these are diverse and can be found in terrestrial and aquatic environments in nature. These are aerobic organisms and Gram-positive organisms. They have different characteristics related to their growth, as they grow in the form of filamentous structures. It contains various sub-orders such as Actinomycineae, Corynebacterineae, Catenulispora, and Micrococcineae.

These can be distributed all over the world as they have the capability to show high versatile nutrition. Thus they can live in any environment and can become a competitor to the organisms present in the surroundings. 

  • Since they can be found in a variety of habitats, they are present in the soil as microorganisms in different types of soil. But several factors can influence these species present in the soil. Some of the factors that influence the growth of these organisms include temperature, pH, and oxygen content present in the soil. These microorganisms are useful as they can break down the tough compounds or the polymers that can range from lignocelluloses to the pectin and also the cell walls of fungi. They can recycle the organic material that is present in the soil and can control the growth of other organisms present in the soil. They can also help to fix the nitrogen content in the soil. 

  • The earthy smell of the soil is due to the activities that are done by actinomycetes in soil when the fresh layer of soil is turned up. They can be found in both freshwater and marine environments. As compared to the freshwater and terrestrial regions the population present in the marine environment is less. They help in the decomposition of several hydrocarbons such as cellulose, alginates, etc. 

  • In compost or manure, the Thermophilic actinomycetes are present. Due to the presence of these organisms the heat production level increases and thus provides a favorable condition for the decomposition. The spores that are present in the soil are hydrated and thus the motile spores are released. There is no evidence to prove the origin of the marine habitats, but the microorganisms are adapted to this environment. They are even capable of surviving in extreme conditions, that include alkalophilic species, psychrophilic species, and halophilic species. 

Actinomycetes Characteristics

Some of the Morphological Characteristics Include:

  • The life cycle of these organisms includes spores and mycelial growth. In the majority of the species, the spore formation includes septation at different stages of aerial hyphae. Thus the plasma membrane is invaded and the inner cell wall breaks down and thickens to form a thick wall. During the process of sporulation, the nuclear material will get divided at the end of the sporulation process. A thick wall is formed around each one of the spores due to the presence of new material. This sporulation process occurs due to the fragmentation of hyphae or due to spore formation. 

  • In the soil or environmental conditions the spores are capable of surviving for a longer period of time. In these conditions, the spores germinate to form germ tubes; these tubes further develop to become mycelium. 

  • They have a cell wall that covers the organism, this cell wall is made up of amino acids, amino sugars, and sugars. It also contains a peptidoglycan layer that is made up of diaminopimelic acid.

  • These are heterotrophic organisms that depend on other organisms for survival. To break down the material that is present in the environment these organisms produce enzymes such as cellulases that help to break down the sugars, proteases help to break down the protein molecules, keratinases help to break down the keratin material and amylases help to break down the starch. 

  • Some of the species of actinomycetes bacteria can have symbiotic relationships with the leguminous plants for survival. 

Points to Remember

  • Actinobacteria is a bacteria that we count in the Gram-positive bacterium phylum.

  • These organisms are terrestrial and aquatic in variation. They are economically essential as they contribute significantly to the soil system, which helps the agriculture and forests sectors.

  • The Actinomycetales are one of the significant members of the order of actinomycetes. They are anaerobic organisms that can diversify and contain several different species.

  • The vital thing to know about actinomycetes is that they are single-celled organisms. They belong to the Actinomycetales order, a type of gram-positive bacteria.

  • We can find them in different parts worldwide and distributed in wide and varied habitats in nature.

  • The term “Actinomycete’’ comes from the Greek words “atkis” which means ray, and “mykes” which means fungi. 

  • This breakdown of the term tells us that the actinomycetes were formerly considered a form of fungi for a long time as they shared some similar characteristics to fungi.

  • Along with the similar characteristics to several fungi groups, they are also nutritionally versatile and capable of producing different types of spores.

  • We can use some members of this group as insecticides and antibiotics. We can do that because they are essential soil organisms capable of producing biologically active compounds.


The actinomycetes help to break down several organic materials that are present in the soil. In agriculture, this process is important because they help to recycle the materials used by plants. They are capable of producing various enzymes that play an important role in industries. Around 75% of the antibiotics are derived from these organisms. One of the major advantages of these organisms is that they produce several bioactive metabolites that are involved in the production of various drugs such as antibiotics, etc.

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FAQs on Actinomycete

1. Are Actinomycetes Fungi or Bacteria?

Actinomycetes are a group of bacteria, but they do share a bunch of common characteristics with fungi. One of the major characteristics involves being able to form hyphae, which is usually a trait of fungi.

The difference between Actinomycete Bacteria and Fungi it resonates with is that Actinomycete Bacteria are different in structure and are unicellular, they are susceptible to penicillin, fungi is not any of this.

Some of the commonly known examples of actinomycetes include Streptomyces, Corynebacterium and Mycobacterium.

2. How do actinobacteria contribute to the soil system?

These bacteria contribute heavily to the soil systems, which then directly help the agriculture and forest sectors.

This contribution happens because the actinobacteria helps decompose dead organic matter and helps the surrounding plants absorb the molecules entirely in the soil. We can also use Actinomycetes as insecticides and antibiotics because they are important soil organisms that can produce biologically active compounds.

They create micro-aggregates in the soil as they bind the soil particles together with the secretion they perform.

So, in general, Bacteria perform many essential duties in the ecosystem, including improving the soil’s structure and aggregation, recycling its nutrients and water.

3. What is the right-hand thumb rule? How is it used?

How do the actinomycetes break down the different types of soil?

  • Actinomycetes are found in different types of habitats, this means they are present in various types of soils as microorganisms. There are still some factors that can influence the species of actinomycetes present in the soil based on the soil’s temperature, pH level, and oxygen content.

  • These microorganisms can break down the tough compounds and polymers that range from lignocelluloses to the pectin and also the cell walls of fungi. They can recycle and control the growth of the organisms and other organic material present in the soil. They also help with the maintenance of the nitrogen content present in the soil.

  • The soil usually has an earthy smell because of the activities performed by the actinomycetes present in that soil when the fresh layer of this soil is turned up. These bacteria can be found in both aquatic and terrestrial areas of our natural habitat. They are usually more in population in the marine areas than the terrestrial ones. The bacteria helps break down the hydrocarbons such as cellulose, alginates, present in the soil.

  • In the composts and manures, the type of actinomycetes that are present are called Thermophilic Actinomycetes. They increase the heat production level of these soils and present us with a favorable condition for the process of decomposition. They hydrate the spores present in the soil and release the motile spores present in the soil. The microorganisms living under this kind of soil are able to survive in the harshest conditions.

4. What is the structure of an Actinomycete?

Some structural features of an Actinomycete are:

  • Actinomycetes have a diameter of 1-2 µm.

  • They generally have a structure that is branches or filamentous, In simple words, they're rod shaped.

  • Most of them are aerobic and their cell wall and internal structures are similar to bacteria. This cell wall consists of mycolic acid.

  • Actinomycetes grow slower than fungi, hence they are also known as “slow growers.”

  • They have 60-78% of G+C content, making them the structures with the highest “G+C” content in the DNA structure.

  • They are found in abundance in marine habitats and the majority of their species are non-motile, encapsulated and non-acidic.

  • Actinomycetes form colonies that range in colors white to yellow.

5. What is the life cycle of an Actinomycete?

These are the following life stages of an Actinomycete:

  • Germination: They disperse in the environment as “Free Spore” and remain dormant until this first stage of germination. The germination process starts when spores are able to get in favorable conditions.

  • Vegetative Growth: Actinomycete has a germ tube that helps in the vegetative growth which gives rise to substrate and aerial hyphae.

  • Coiling: Sometimes Actinomycetes turn intro spiral forms due to unfavorable conditions.

  • Septation: This is the stage where we observe a formation of septum between the vegetative hyphae.

  • Spore Maturation: Now the septum inside the hyphae saturates and forms a spore chain. 

  • Release: After this the spores release the life-cycle ends.