Bioemulsifier production by Aspergillus niger MYA 135: presumptive role of iron and phosphate on emulsifying ability

Abstract

Microbial emulsifiers are compounds employed in primary mechanisms for bioremediation of petroleum and other hydrocarbon pollutants from the environment. Although emulsifiers of biological origin are produced by microorganisms generally in response to growth on hydrocarbons, Aspergillus niger MYA 135 produced a bioemulsifier during fermentation in a sucrose-based culture medium at an initial pH of 5.0 and at 30°C. The production of bioemulsifiers can be strongly influenced by environmental factors. In this connection, a study of the effect of initial pH, the incubation temperature and presence of CaCl₂ or FeCl₃ in the culture medium was conducted. Emulsification index was increased by 112 and 206% at an initial pH 2.0 or in medium supplemented with FeCl₃, respectively. On the other hand, emulsifying ability of Aspergillus niger supernatants was detected during the exponential phase, suggesting that bioemulsifiers accumulation and microbial growth would be related. Interestingly, this study suggests that iron and/or phosphate ions would play a key role in maintaining the emulsifying ability. Finally, factorial design was also employed to study the effects of the initial pH, the presence of FeCl₃ and the concentration of KH₂PO₄ on the emulsification index.