Actinomycetes

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Overview

Actinomycetes bacteria by Oregon Caves from Cave Junction, USA / CC BY (https://creativecommons.org/licenses/by/2.0)

Actinomycetes is a nontaxonomic term for a group of common soil microorganisms sometimes called "thread or ray bacteria." They are a versatile group of Gram-positive, rod shaped and spore forming bacteria widely distributed in the terrestrial and aquatic environments [6]. These are prokaryotic organisms that are classified as bacteria, but are unique enough to be discussed as an individual group [7]. The specialty of the actinomycetes is that they have a mycelial appearance unlike most bacteria [2]. These bacteria are rather unexplored because the cultivation and maintenance of actinobacteria are not that easy as in the case of other bacteria. They are an important component of the bacterial communities, especially under conditions of high pH, high temperature or water stress. Although they were originally recognized as soil microorganisms, it is now being recognized that marine actinomycetes are also important. Actinomycetes are heterotrophic in nature. Most of them are strict saprophytes, while some from parasitic or mutualistic associations with plants and animals [1]. One distinguishing feature of this group of bacteria is that they are able to utilize a great variety of substrates found in soil, especially some of the less degradable insect and plant polymers such as chitin, cellulose and hemicellulose [7].

Distribution & Ecology

Actinomycetes can be found in a wide range soil and marine habitats in different parts of the world. Because they can live in different environments and exhibit high versatility in their nutrition, this allows them to spread and thrive in different regions across the globe and compete with other organisms in their surroundings. While Actinomycetes can be found in a variety of habitats, they constitute a huge extent of the microbial population in many soils. Thus making them some of the most common micro-organisms in different types of soil (about 1 million cells per gram of soil). However, a variety of factors like pH, oxygen, and temperature influence the species that inhabit different types of soil [3]. It has been found that the pH is a major environmental factor determining the distribution and activity of soil actinomycetes as Neutrophils' occur in less number in acidic soils below pH 5.0, whereas acdophilic and acidoduric streptomycetes are more numerous in acidic soils [1]. The biggest groupings of actinomycetes in the soil can be found in the organic horizon. Actinomycetes may assume a part in advancing plant development, through control of root pathogens or in some aberrant route, since a few species can produce antifungal compounds [4]. It is also important to note that there is evidence that actinomycetes usually form a small fraction of the bacterial flora in marine habitats, but population numbers are lower compared with those from terrestrial and freshwater sites. Apart from their wide distribution, Actinomycetes are also nutritionally versatile and capable of producing different kinds of spores, allowing them to successfully compete with other organisms in their surroundings.

Significance

Actinomycetes have several key roles in their ecosystems. Scientists have long known that actinomycetes keep soil bacteria populations in balance. They have the ability to break down various organic materials in soil as well as their ability to produce a range of bioactive molecules, including antibiotics and various kinds of enzymes. With this, about 15% of the world's nitrogen fixed naturally is from symbiotic relationships between various species of the Frankia family of actinobacteria and their host plants. Their role in the decomposition of plant and other material especially in the degradation of complex and relatively recalcitrant polymers is hugely important [3]. Lignin, cellulose and lignocellulose are all examples of what they degrade. There is evidence that actinomycetes are involved in the degradation of many other naturally occurring polymers in soil such as hemicellulose, pectin, keratin, chitin and fungal cell wall material [1]. Given that they help recycle materials that can be used by plants, it is beneficial in agriculture practices. They also produce a variety of enzymes that are useful in various industries, such as the medical industry. As they are known for their ability to produce various antibiotics, the actinomycetes are widely explored by various research groups in search of novel drug molecules. Another significance of these bacteria is that from the rhizosphere, they suppress the growth of pathogens. Since they produce various bioactive metabolites that are used to produce various drugs (antifungal, anti-parasitic and antibiotics etc). Actinomycetes are an ecologically important group, which play a crucial role in several biological processes such as biogeochemical cycles, bioremediation, bio-weathering and plant growth improvement [5].


Scanning electron micrograph of Actinomyces israelii By GrahamColm at English Wikipedia, https://commons.wikimedia.org/w/index.php?curid=4197579

References

  • [1] C. Dilip V., Mulaje S. S., Mohalkar R.Y. 2013, May. A REVIEW ON ACTINOMYCETES AND THEIR BIOTECHNOLOGICAL APPLICATION | International Journal Of Pharmaceutical Sciences And Research.
  • [5] Bawazir, A. M. A., M. Shantaram. 2018. ECOLOGY AND DISTRIBUTION OF ACTINOMYCETES IN NATURE– A REVIEW. International Journal of Current Research 10:5.
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