Isolation, characterization, and optimization of biosurfactant production by an oil-degrading Acinetobacter junii B6 isolated from an Iranian oil excavation site

Abstract

An enrichment program for hydrocarbon-utilizing bacteria capable of biosurfactant production isolated from soil samples was carried out on mineral salt medium supplemented with Iranian light crude oil (ILCO, 1%). The most promising isolate was identified as Acinetobacter junii B6 using 16S rDNA sequencing and biochemical characterization. Time course profile of biosurfactant production using A. junii B6 showed surface tension reduction in the culture broth to 45 mN/m after 48 h incubation and a 51% emulsification of ILCO. Scanning electron microscopy (SEM) analysis of A. junii B6 showed the tendency of bacterial cells to adhere to each other and to the oil droplets. Application of two-level fractional factorial design showed that surface tension of culture broth was maximally reduced to 38 mN/m in the presence of NaNO3 (2 g/L), ILCO (5%), temperature of 25 °C, aeration rate of 300 rpm, and inoculum size of 2%. GC-MS analysis of the culture broth showed the ability of A. junii B6 to degrade most of the alkanes' components of ILCO when used as sole carbon source. Both strain and product has potential applications in various oil industries including bioremediation and enhanced oil recovery.