The production and physicochemical properties of a biosurfactant mixture obtained from Sphingobacterium detergens

The commercial application of a new biosurfactant such as the one produced by Sphingobacteriumdetergens needs a cost-effective process and knowledge of its properties. In the present study, a specific medium and a downstream process have been developed to enhance biosurfactant production. Optimal concentrations of nutrients in MCA medium were (g/L) the following: KH2PO4, 1; K2HPO4, 2; CO(NH2)2 0.88; CaCl2 0.01; FeSO4·7H2O, 0.01; MgSO4·7H2O 0.5; KCl, 1.0; trace elements 0.05 mL. Biosurfactant production in the MCA medium required a bacterial co-metabolism of glucose and an n-alkane. A fed-batch culture with supernatant lyophilization prior to organic extraction produced 466 mg/L of organic extract, which represents a 6.9-fold increase in production. The newly obtained biosurfactant was a complex mixture of molecules. The three characterized fractions consisted of the complete fraction and two second-level purification fractions with apolar and polar characteristics. The complete and apolar fractions have been shown to self-aggregate in the form of lamellar liquid crystals at a high concentration and bilayers at lower concentrations. Negatively charged particles were identified, which were neutralized at a low pH with a concomitant increase in size. The pH affected the surface tension of the solutions congruently with phosphate headgroups.

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► A complex mixture of surfactants is produced by Sphingobacterium detergens.
► Biosurfactant production by S. detergens is carbon co-metabolism dependent.
► Biosurfactant can be separated in two fractions of different polarity.
► Surface tension and aggregation depend strongly on the fraction and pH.