3.3. Surface tension analysis and biosurfactant stability
One important property of the surfactants is to reduce the ST
of the medium that determines the rate of degradation of hydrophobic
substrates [32]. The cell surface activity of the biosurfactant
produced by Bacillus sp. USTBa was measured at different
time intervals and is displayed in Fig. 2. The ST of the culture
medium decreases from 63 to 28 mN/m during growth of Bacillus
sp. USTBa on crude oil for 192 h. Afterwards, no further decrease
in ST was observed on prolonged growth. The change in ST and
emulsification activity of the crude oil demonstrates that the
biosurfactant was produced by Bacillus sp. USTBa during biodegradation
process of crude oil [33] and is in consistent with the
literature [31]. Thus, understanding the relationship between
the surface properties of microbial degraders and biosurfactants
is of paramount importance for their proper use in
bioremediation.