Emulsification Properties of Bioemulsifiers Produced by Wild-Type and Mutant Bradyrhizobium elkanii Strains

Abstract

The use of biosurfactant is a promising alternative over the chemical surfactant as they are better biodegradable and do not pollute the environment. To date, there is little information on the biosurfactant producing microorganisms belonging to different Rhizobium and Bradyrhizobium species. In this study, the emulsifying properties of both culture media and a substantially cell-free medium from bacterial cell cultures in which B. elkanii SEMIA 587 or mutant strains cultivated in defined media supplemented with sucrose were determined by measuring the emulsifying activity, which determined the ability of biosurfactant in forming oil-water emulsion, and emulsifying index (E24), which determined the capacity of surfactant in forming emulsions on different hydrophobic substrates (soybean oil, sunflower oil or diesel oil). The performance of strains as bio emulsifier were very contrasting as shown by their specific emulsification indexes with different substrates, beginning at 24 hours. Regarding emulsifying index for cells, best result of E24 was obtained by using sunflower oil for wild type and mutants with exception for 587::TnphoA31 that witch got better results in soybean oil. However, analysing using cell-free medium have shown higher E24 values mostly in soybean oil except for 587::TnphoA31 and 587::TnphoA50 which have performed better in diesel oil. This finding indicates a probable production of bioemulsificants that adhere to the cell wall of this bacterium and are extracellular. The same E24 value (79.17%) was observed in the case of soybean oil with culture medium from both the wild-type and the mutant strain 587::TnphoA50. The emulsification capacity was very sensitive to the temperature, pH and NaCl concentration changes. These results demonstrate that the Bradyrhizobium strains could be attractive for use in biosurfactants applications, these products is great due to growing demand for biodegradable and environmentally friendly analogues for synthetic chemicals.