Nutrition, Cultivation and Isolation of Actinomycetes

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Chapter: Pharmaceutical Microbiology : Nutrition, Cultivation and Isolation of microorganisms : Bacteria-Actinomycetes-Fungi-Viruses

Actinomycetes refers to any bacterium of the order Actinomycetales, which essentially includes the families : Mycobacteriaceae, Actinomycetaceae, Actinoplanaceae, Dermatophilaceae, Micromonosporaceae, Nocardiaceae, and Streptomycetaceae.


ACTINOMYCETES

 

Actinomycetes refers to any bacterium of the order Actinomycetales, which essentially includes the families : Mycobacteriaceae, Actinomycetaceae, Actinoplanaceae, Dermatophilaceae, Micromonosporaceae, Nocardiaceae, and Streptomycetaceae.

 

In fact, Actinomyces represents a genus of bacteria belonging to the family Actinomycetaceae which contain Gram-positive staining filaments. In general, these organisms cause various diseases both in humans and animals.

 

Another school of thought describes actinomycetes as the filamentous microorganisms. It has been duly observed that superficially their morphology very much looks alike that of the filamentous fungi. Nevertheless, the filaments of actinomycetes invariably comprise of the prokaryotic cells hav-ing diameters relatively much smaller in size in comparison to those of the molds. However, there exist certain typical actinomycetes which resemble the molds by making use of externally carried asexual spores for accomplishing the desired reproduction.

 

Interestingly, actinomycetes are very common inhabitants of soil, whereas filamentous habit of growth has definitely the added advantages. In this manner, the organism can conveniently bridge the water-free gaps existing between the soil particles to allow them to migrate to a new nutritional site. It is pertinent to state here that this ensuing particular morphology very much provides the organisms an appreciably higher surface-area-to-volume ratio, thereby the nutritional efficiency gets improved significantly in the highly competitive soil environment.

 

Importantly, the best-known genus of actinomycetes is Streptomyces, which is one of the bacteria most abundantly isolated from soil.

 

However, the reproductive asexual spores of Streptomyces, termed as conidiospores, are invari-ably formed at the ends of aerial filaments. If each conidiospore gets attached to an appropriate substrate, it is capable of germinating into an altogether new colony.

 

Characteristic Features of Streptomyces : The various characteristic features of Streptomyces are as follows :

 

(1) These organisms are strict aerobes.

 

(2) They invariably give rise to extracellular enzymes which essentially enable them to use proteins, polysaccharides viz., starch or cellulose ; and many other organic compounds usually found in soil.



 

(3) It gives rise to the formation of a gaseous compound known as geosmin, that imparts to the ‘fresh soil’ its typical musty odour.

 

(4) The species of Streptomyces are of immense value because they categorically produce a host of commercial antibiotics, such as :

Streptomyces nodosus : Amphotericin B

Streptomyces venezuelae : Chloramphenicol

Streptomyces aureofaciens : Chlorotetracycline and tetracycline.

Streptomyces erythraeus : Erythromycin

Strepromyces fradiae : Neomycin

Streptomyces noursei : Nystatin

Streptomyces griseus : Streptomycin

 

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