Extracellular biosurfactant was obtained from the supernatant
of the exhausted fermentation culture broth after centrifugation
(Ortoalresa, Consul 21, EBA 20, Hettich Zentrifugen, Germany) at
2755 × g for 15 min and 4 ◦C. The precipitate (biomass pellet) was
resuspended with distilled water in the original volume of culture
broth in order to avoid dilution, washed twice with distilled water
using a vortex (Classic, Velp Scientific, Italy) at 3000 rpm for 5 min,
then it was centrifuged at the same conditions mentioned above to
obtain cell-bound biosurfactant suspended in supernatant.
Both supernatants, extracellular and cell-bound biosurfactants,
were used to determine the surface tension (ST) using a Krüss ten-
siometer equipped with a 1.9 cm Du Noüy wettable platinum ring
at room temperature following the ring method (Kim et al., 2000).
Biosurfactant activity of strain ZSB10 was determined measuring
the surface tension reduction (ST).