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ABSTRACT
Acinetobacter radioresistens, a Gram-negative bacterium isolated
from the sludge of waste water, produces an extracellular lipase
(triacylglycerol acylhydrolase, EC 3.1.1.3), which has a high
activity in alkaline pHs. This study intended to examine the
effect of equipping a non-woven fabrics in a 2-L tank fermentor
on the production of A. radioresistens lipase by batch
fermentation.The non-woven fabrics was made from nylon 6 coated
with a hydrophobic acrylic resin.
It was found that, in the free-cell fermentation with n-
hexadecane as the carbon source, the cells entered the
exponential growth phase at 75 h, and the maximum lipase yield
was 23 U/mL at 102 h. In the non-woven-fabrics system, however,
the cells entered the exponential growth phase earlier (at 60
h), the cell concentration attained was higher, and the lipase
yield increased to 53 U/mL at 167 h. When the medium was
supplemented with 0.1% olive oil, the lipase yield obtained in
the free-cell system was 16U/mL at 21 h, owing to excessive
foaming occurred at 20 h; in contrast, the lipase yield was 71
U/mL at 84 h if using the non-woven-fabrics system. In
addition, excessive foaming was not observed in the latter
system. The results obtained with the non-woven-fabrics system
were found comparable to that of the free-cell system where gum
arabic was added to emulsify n-hexadecane.
Based on these findings, the roles of the non-woven fabrics in
the fermentation with A. radioresistens can be pictured: (1) it
helps the dispersion of n-hexadecane to very fine oil droplets,
and thus favors cell growth and lipase production; and (2) it
can adsorb surface active agents produced during the
fermentation, and thus suppress the foaming.
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