Effects of ethanol and phosphate on emulsan production by Acinetobacter calcoaceticus RAG-1

Abstract

To enhance emulsan production, the effects of ethanol and phosphate on cell growth and emulsan synthesis by Acinetobacter calcoaceticus RAG-1 were investigated in batch cultivations. It was observed that an optimal concentration of ethanol and phosphate existed for the maximization of emulsan production in batch cultivations. High concentrations of ethanol (above 10 g l −1) inhibited cell growth, which resulted in decreased emulsan synthesis rates. Optimum level of ethanol for emulsan production (about 6.5 g l −1) was decided to maximize the specific growth rate and specific production rate of emulsan. High concentrations of phosphate (above 18.15 g l −1) inhibited cell growth and emulsan production. The intracellular phosphate level affected the specific growth rate. The optimum level of phosphate for emulsan production (about 12.1 g l −1) was identified in order to maximize the specific growth rate as well as the specific production rate. In a fed-batch cultivation, high volumetric production of emulsan was achieved by continuous feeding of ethanol and phosphate to maintain ethanol and phosphate concentrations at the optimal level.