Abstract
The strain producing biosurfactant was isolated from soil smples. The isolated strain was identified as the genus Nocardia through its morphological, cultural and physiolgical characteristics. A high concentration of the biosurfactant by Nocardia sp. L-417 was obtained after 4 days of cultivation in the culture medium containing 3% n-hexadecane, 0.1% $NaNO_3$, 0.02% $K_2HOP_4$, 0.01% $H_2PO_4$, 0.01% $MgSO_4$.$7H_2O$, 0.01% $CaCl_2$, 0.02% yeast extract, and 0.02% tryptone. The optimum pH and temperature for biosurfactant production were pH 6.0 and $30^{\circ}C$, respectively. Furthermore, most biosurfactans were produced during the exponential growth phase, and this fact indicated that the biosurfactans production was growth-associated. The biosurfactant showed the good emulsification activities on various emulsifying substrates such as bunker A, paraffin, corn oil which are used widely in industries.
Biosurfactant를 생산하는 미생물을 토양으로부터 분리하였다. 그 중에서 표면장력 및 계면장력 감소능에서 가장 우수한 L-417주를 순수분리하여 동정한 결과, No-Cardia속으로 판명되었다. Biosurfactant 생산을 위한 최적 배지조성은 3% n-hexadecane, 0.1% $NaNO_3$, 0.02% $K_2HPO_4$, 0.01% $KH_2PO_4$, 0.01% $MgSO_4 \;.\;7H_2O$, 0.01% $CaCl_2$ 0.02% yeast extract였으며, 최적 온도와 pH는 각각 $30^{\circ}C$와 6.0이였다. 이러한 조건에서 500ml용 shaking flask에 최적 배지 50ml를 넣어 배양했을 경우 대수증식기 말기인 4일째에 균의 증식과 유화활성이 가장 높게 나타남에 따라 Nocardia sp. L-417에 의한 bio-surfactant의 생산은 균의 생육과 밀접한 관련이 있는 것으로 판단된다. 이계면활성제는 산업적으로 널리 사용되는 bunker A, paraffin, corn oil 및 oilve oil 등에 대해서도 비교적 높은 유화활성을 나타내였다.