Potential bifunctional rhizobacteria from crude oil sludge for hydrocarbon degradation and biosurfactant production

Abstract

Biosurfactant produced by rhizobacteria has the potential to enhance the degradation of hydrocarbons, leading to more efficient phytoremediation. The aim of this work was to search for bifunctional hydrocarbon-degrading and biosurfactant-producing rhizobacteria. Isolation of bacteria was conducted from three sources (A: rhizosphere of Scirpus grossus planted in garden soils and B: rhizosphere of S. grossus planted in crude oil sludge and C: crude oil sludge) prior to degradation test. Seven isolated rhizobacteria from source B (coded as B1–B7) were screened for a hydrocarbon degradation test with an initial total petroleum hydrocarbon content of 56.13 mg/g. Similar isolated rhizobacteria were also found in source A and C. The best three isolates (B1, B3 and B6) and mixed culture of them, significantly degraded hydrocarbon with 16.2%, 8.4%, 39.7% and 34.8% removals, respectively. Subsequently, the three pure rhizobacteria and their mixture (B1 + B3 + B6) were screened for biosurfactant production through tests of oil displacement, drop collapse, emulsification and surface tension. All the pure rhizobacteria and mixed culture had given positive response for all the tests. The presence of biosurfactant produced by rhizobacteria was confirmed by SEM images in which the formation of exopolymers interconnecting individual cells into a complex network of mass was formed due to biosurfactant extraction from bacteria cell. Thus, the three isolated rhizobacteria (B1, B3, and B6), later identified as Bacillus sp. strain SB1, Bacillus sp. strain SB3 and Lysinibacillus sp. strain SB6, respectively, and their mixed culture can simultaneously biodegrade hydrocarbon and produce biosurfactant to enhance the degradation process.