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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