Physical and chemical properties of a biosurfactant synthesized by Rhodococcus species H13-A

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Abstract
The chemical and physical properties of a biosurfactant synthesized by hexadecane-grown Rhodococcus species H13-A are described. The biosurfactant is an anionic glycolipid consisting of 1 major and 10 minor components. The hydrophilic portion of the molecule is trehalose, which is acylated with normal C10 to C22 saturated and unsaturated fatty acids, C35 to C40 mycolic acids, hexanedioic and dodecanedioic acids, and 10-methyl hexadecanoic and 10-methyl octadecanoic acids. The major glycolipid species was identified as 2,3,4,6,2′,3′,4′,6′-octaacyltrehalose, plus minor glycolipid species of di-, tetra- and hexa-acyltrehalose derivatives. The glycolipid exhibited a critical micelle concentration of 1.5 mg/mL and minimum interfacial tension value of 2 × 10−2 mN/m against decane, with a further reduction in interfacial tension to 6 × 10−5 mN/m in the presence of the cosurfactant pentanol. The phase behavior of the glycolipid indicates the formation of a surfactant-rich, "middle-phase" microemulsion containing liquid crystals, both of which are associated with surfactant systems having ultralow interfacial tension values. Key words: trehalose lipids, glycolipids, biosurfactants.