Production Of Antimicrobial Compounds From A Local Marine Bacterial Isolate, Bacillus Sp. (S1A4)
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Date
2007-03
Authors
Hui Ming, Lim
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Abstract
A total of 160 strains of marine microorganisms were supplied by the
Fisheries Research Institute, Penang. They were collected from samples all over
the shores of Malaysia. Out of those, 134 were bacterial strains, 9 actinomycetes, 3
fungal and 14 yeast isolates. About 113 isolates were found to produce pigments.
Non - pigmented strains (white colonies) were the most commonly found (26%)
while the yellow coloured strains followed with a close second (25%), orange
pigmented isolates (16%), and the rest were brown, beige, light green, dark blue,
red, grey and transparent isolates in a small percentage. Among the marine
isolates provided, only 88 isolates were tested for antimicrobial activity. 59.1 %
exhibited antimicrobial activity (52 isolates) of which, 50.0% (42 isolates) exhibited
antibacterial activity, 10.3% (9 isolates) antifungal activity and 10.2% (9 isolates
exhibited both antibacterial and antifungal activities. The distribution of the
antimicrobial compounds in the three selected isolates showed that ali of them
produced both extracellular and cell - bound antimicrobial compounds. The isolate
S 1 A4 was chosen for further experiments because it exhibited a wide spectrum of
activity, was easily subcultured, and grew well in the cultivation medium. The
isolate S 1 A4 was identified as the genus Bacillus sp. The production of
antimicrobial compounds was enhanced by optimizing physical (culture conditions)
and physiological (medium compositions) conditions. The optimized cultural
conditions were: 150 rpm for the agitation speed, 4% (v/v) of 3 x 108 cells/ml of the
inoculum size, initial pH medium of 7.3 and the incubation temperature was fixed at
3rC. About 50ml of natural filtered sea water was used in making the cultivation
medium which consisted of 0.40% (w/v) of starch, 0.50% (w/v) of peptone, 0.20%
(w/v) of yeast extract, 0.01 % (w/v) of ferric phosphate, 0.09% (w/v) of L-arginine
and 0.05% of KC!. Even though the production of antimicrobial compounds started
during its exponential growth phase, maximum production was achieved during the
idiophase. After optimization using the shake flask system, there was an increase
of 29.6 U/ml or 39.6% increment in antimicrobial compound production. After
optimization in the shake flask system, a tubular airlift fermenter with a 2.0L
capacity was used for scaling up and then all the parameters were again
reoptimized. The optimized conditions were: 4 IImin of aeration, 4% (v/v) (3 x 108
cells per ml) of initial inoculum size and initial pH of 7.3. Filtered natural sea water
was used in making the medium which consisted of : 0.5% (w/v) of starch, 0.6%
(w/v) peptone, 0.2% (w/v) of yeast extract, 0.01 % (w/v) ferric phosphate, 0.09%
(w/v) of L-arginine and 0.05% of KC!. An increment of about 13.8% (4.1 U/ml) of
antimicrobial compound production was obtained after optimization in a tubular
airlift fermenter. Characterization of the crude extract of the antimicrobial compound
found that it was thermostable in a temperature range between 35"C - 65°C, and
pH stable between the pH values between 6 -10. The antimicrobial compounds
exhibited bactericidal activity against the cells of Staphylococcus aureus .SEM and
TEM micrographs showed that the antimicrobial compound lysed the cell wall of S.
aureus besides interfering with the intemal structure of the ceils.
Description
Keywords
Antimicrobial Compounds , Bacillus Sp. (S1A4)