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What Are Actinomycetes?

Actinomycete is a heterogenous group of bacteria that are gram-positive, filamentous, with a branched growth pattern. They grow in mycelium or extensive colonies. Though they are bacteria, they are a group of unique organisms that can be studied separately.

Actinomycetes Classification

Kingdom	Bacteria
Phylum	Actinomycetota
Class	Actinomycetia
Order	Actinomycetales

Characteristics and Morphology

They are prokaryotic and range in size from 1-2 µm in diameter.
They are mostly aerobic organisms but some can be anaerobic as well.
They inhabit the soil commonly, but may be found in marine environments as well.
The mycelium of actinomycetes sometimes breaks apart to form coccoid or rod-shaped colonies.
Many members of actinomycetes are also known to form spores with the sporangia or spore case being found on the aerial hyphae.
They are easily infected by bacteriophages, and the phages that infect actinomycetes are called actinophages.
They sometimes possess a flagella that gives them motility.
The members of the group range from harmless bacteria to pathogenic species to extremely useful antibiotic producers.
They sometimes resemble the hyphae of fungal species; however, they can be distinguished on the basis of size, the actinomycetes being much smaller.
They are able to act on different soil substrates such as less degradable insects and plant polymers such as cellulose, chitin and hemicellulose.
They are found in an abundance of 5-40 CFU/ml in the marine environment.
In soil, they are found in the abundance of 10⁶-10⁸/g.

Actinomycetes Examples

Nocardia asteroides

Nocardia uniformis

Actinomyces sp

Streptomyces griseus

Streptomyces venezuelae

Micromonospora purpurea

Reproduction

Reproduction in actinomycetes is through hyphae fragmentation or spore formation. At the time of reproduction, they form either conidiophores, oidiospores or sporangiospores. During fragmentation, the members of the group form hyphae up to one-fifth or half the size of fungal hyphae.

Uses

They produce a compound called geosmin, that gives the earthy colour to the soil.
They can degrade complex molecules such as cellulose and chitin.
The genus Frankia is a diazotroph that is capable of biological nitrogen fixation.
The genus Streptomyces is highly useful as it can produce antimicrobial compounds such as streptomycin, streptothricin and actinomycin.
The actinomycetes are an important source of antimicrobial compounds, they produce up to two-thirds or about 61% of the total antibiotics.

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Frequently Asked Questions

Are actinomycetes bacteria or fungi?

Actinomycetes are a group of gram-positive bacteria.

Where are actinomycetes found?

Actinomycetes are found in both soil and marine environments.