2.1.2. Microorganism strain and biosurfactant production
The strain used in the present work is B. subtilis SPB1 (GenBank
accession HQ392822), a wide type isolated in our laboratory from a
Tunisian soil contaminated by hydrocarbons, as reported by Ghribi
et al. (2012). B. subtilis SPB1 was shown to produce a highly effective
biosurfactant that belongs to the class of lipopeptides. It was
selected on the basis of the high haemolytic and emulsification
activities of its biosurfactant which could reduce surface tension
of the water from 70 to 34 mN m1 (Ghribi et al., 2011). B. subtilis
SPB1 strain was streaked on a nutrient agar slant and incubated at
37 C. After 24 h, one loop of cells was dispensed in 3 ml of LB medium
and incubated overnight at 37 C. Aliquots (0.2 ml) were used
to inoculate 250 ml Erlenmeyer flasks containing 50 ml LB medium
and incubated in a rotatory shaker at 200 rpm and 37 C overnight.
Three ml of the obtained culture were used to inoculate the production
medium. B. subtilis SPB1 biosurfactant production was performed
in 250-ml Erlenmeyer flasks containing 50 ml of the liquid
mineral optimized medium, described in a previous work by Mnif,
Ellouze-Chaabouni, and Ghribi (2012). At the end of the cultivation,
the culture was centrifuged at 10,000 rpm and 4 C for 20 min to
remove bacterial cells.
2.