Biosurfactant production and diauxic growth of Rhodococcus aurantiacus when using n-alkanes as the carbon source

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Abstract
When grown on hydrocarbons, Rhodococcus aurantiacus produced four glycolipid biosurfactants which could lower the surface tension of distilled, deionized water to between 26 and 30 nM∙m−1. The biosurfactants were found both extracellularly and associated with the cells. They could be extracted with solvents such as chloroform and pentane. Greater quantities of biosurfactant were produced when NaNO3 was used in place of (NH4)2SO4 as the nitrogen source. When grown on n-alkanes using (NH4)2SO4 as the nitrogen source, R. aurantiacus exhibited an unusual form of diauxic growth. Data suggested that the mechanism of diauxy involved changes in the degree of cell-surface hydrophobicity which resulted in hydrocarbon-transport limitation.