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 having
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 thebacteria most abundantly isolated from soil.
However, the reproductive asexual spores of
Streptomyces, termed as conidiospores, are invariably
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
: NystatinStreptomyces griseus : Streptomycin