Screening, isolation, and process optimization of a bioemulsifier-producing Acinetobacter Y-1.

Optimizing the production of bioemulsifiers is critical for sustainable industrial applications. In this study, 27 strains were isolated from activated sludge, and strain Y-1 was identified as the most promising candidate based on emulsification index (EI) and emulsification rating. Strain Y-1 exhibited excellent emulsifying and dispersing activities toward both liquid paraffin and crude oil, with an EI of 65%. Morphological characterization, physiological and biochemical tests, and 16S rDNA sequencing identified Y-1 as a member of the genus Acinetobacter. Fermentation conditions were optimized using single-factor experiments and response surface methodology, and the optimal conditions were determined to be a carbon-to-nitrogen (C/N) ratio of 1:1, inoculum concentration of 2%, and incubation temperature of 34 °C. Under these conditions, the bioemulsifier yield of Acinetobacter Y-1 reached 6.9 g/L, representing a 4.14-fold increase compared to unoptimized conditions. The bioemulsifier produced by Acinetobacter Y-1 effectively emulsified a variety of hydrocarbon substrates, including liquid paraffin, diesel, xylene, olive oil, cutting oil, cold rolling oil, n-hexane, and benzene. Furthermore, it retained stable emulsification activity under extreme conditions, including a wide temperature range (4-80 °C), high salinity (5-30%), and broad pH values (1-14). These findings highlight Acinetobacter Y-1 as a promising strain for the production of high-activity, stable bioemulsifiers with great potential for industrial applications.