Batch growth studies ofRhodococcus rubraon different substrates using 3.34 Czapek medium supplemented with 0.2 sodium propionate, nutrient broth, starch and ammonium sulphate respectively were investigated. A 3.34 Czapek medium supplemented with a range of concentrations (0#x2013;1) of yeast extract were also investigated in order to maximise the biomass concentration and the surface activity related to the cells. Results suggest that both the biomass concentration and the amount of surface active materials which are produced during growth are dependent upon the quantity and the nature of the substrate. Results using starch as a nutrient source suggest the production of a potent biosurfactant whose surface activity can bring a marked decrease in surface tension. In addition, high growth does not necessarily impart greater surface activity to the cells. Growth inhibition studies using sodium laurate were carried out and the results suggest thatR. rubracannot be grown in a broth containing 50mg l#x2212;1of this chemical. This was substantiated by pH measurements which were made during the work.
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