Discussion
A broad-spectrum antibiotic producing alkaliphilic actinomycetes
isolate A2D from phoomdi in Loktak Lake of Manipur,
India has been characterised and identified as
S. tanashiensis strain A2D. It was found that the antibiotic
production by S. tanashiensis A2D was positively affected by
the carbohydrates, nitrogen sources and NaCl.
The results showed that antibiotic production was higher
in medium having glucose (1%) as carbon source. The growth
as well as antibiotic production got reduced with the
increase or decrease of glucose concentration. This result
is quite comparable with S. sannanensis strain RJT-1, for
which glucose was found to be suitable carbon source for
the antibiotic production [31], while dextrose prove to be
the best carbon source for antibiotic production by
S. kanamyceticus M27 [21]. Similarly, Cruz et al. [3] reported
that the production of antibiotic by S. griseocarneus was
increased by glucose. High concentration of glucose is generally
regarded as repressor of secondary metabolisms [4] and
maximum cell growth rates can inhibit antimicrobial agent
production [8]. An example of catabolic repression of secondary
metabolism in actinomycetes is that of actinomycin
synthesis by S. antibioticus after more glucose is added to
the media [6].
Among the organic and inorganic nitrogen sources tested,
maximum antibiotic production was obtained with soyabean
meal indicating that the level of antibiotic production may
be greatly influenced by the nature and type of the nitrogen
source supplied in the culture medium. In comparison with
inorganic nitrogen sources, organic nitrogen sources gave
relatively higher antimicrobial agent production by the strain
A2D. This is in conformity with the findings of Yu et al. [36]
for which defatted peanut powder proved to be the best
nitrogen source for antibiotic production by S. rimosus MY02.
Vahidi et al. [30] reported that organic nitrogen sources are
better for the production of antifungal agents in their study.
Optimum salt requirement for antibiotic production was
examined in the improved medium containing glucose and
soyabean meal supplemented with different salt concentration
(0—5%). Antibiotic production was optimum at 2% NaCl,
with slight decrease at 3 and 4%. The strain A2D can grow up
to 7% NaCl. Saha et al. [24] reported the antimicrobial
potential of actinomycetes isolate that grew in the presence
of 20% (w/v) NaCl, while antibiotic production being maximum
with 5% (w/v) NaCl in the production medium.
The results indicated the dependence of the antibiotic
synthesis on the medium constituents. In fact, it has been
shown that the nature of carbon and nitrogen sources strongly
affect antibiotic production in different organisms [32].
Antibiotic production and growth was found to be optimum
at pH 8, whereas at pH 10, there was no antibiotic
production. The results are comparable with some Streptomyces
species recorded to produce antibiotics against bacteria,
fungi and yeast at alkaline pH [1]. The strain A2D
showed a narrow range of incubation temperature for relatively
good growth and antibiotic production. Highest growth and antibiotic production was obtained at 28 8C. The temperature
range adequate for good production of secondary
metabolites is narrow, for example, 510 degrees [14].
The environmental factors like incubation temperature,
pH and incubation period were also found to have profound
influence on antibiotic production by S. tanashiensis A2D as
surveyed in streptomycetes by other investigators [28].