Exploration and characterization of a newly isolated bacterium, Enterobacter quasihormaechei strain BDIFST24001, capable of producing rhamnolipid biosurfactant for oil remediation

Abstract

Biosurfactants are naturally occurring compounds synthesized by micro-organisms that increasingly attract attention due to both their living area and application in various industries. In this study, we explore and characterize a novel bacterium, Enterobacter quasihormaechei strain BDIFST24001, isolated for its ability to produce rhamnolipid biosurfactants, with the aim of facilitating oil remediation processes. The isolation of this bacterium was carried out using Luria-Bertani (LB) broth media from environmental samples collected from oil-contaminated sites in Dhaka City. Screening tests, including the oil spreading method and drop collapse assay, were conducted to identify potential biosurfactant-producing strains, leading to the selection of E. quasihormaechei strain BDIFST24001 based on its favourable performance. Subsequent molecular identification revealed a high similarity of the strain’s 16S rRNA gene to E. quasihormaechei, which was corroborated through phylogenetic analysis. Further analysis of the biosurfactant produced by this strain indicated its rhamnolipid nature, as confirmed by FT-IR spectroscopy. The rhamnolipids exhibited promising surface-active properties, including a significant reduction in surface tension and emulsification activity, as evidenced by surface tension measurements and emulsification index assays. Optimization studies revealed that the optimal conditions for rhamnolipid production by E. quasihormaechei strain BDIFST24001 were a temperature of 37 °C, pH 10.0 and salinity of 4 %. The rhamnolipids produced by this strain demonstrated effective oil remediation capabilities, as observed through controlled experiments using petrol oil. The rhamnolipids effectively reduced the surface tension of the oil–water interface, facilitating the dispersion and emulsification of the oil phase in water. Overall, our findings highlight the potential of E. quasihormaechei strain BDIFST24001 as a promising candidate for biosurfactant-mediated oil spill cleanup and environmental remediation efforts.