Rhamnolipid production using Shewanella seohaensis BS18 and evaluation of its efficiency along with phytoremediation and bioaugmentation for bioremediation of hydrocarbon contaminated soils

This study reports the combined use of a rhamnolipid type biosurfactant (BS) along with phytoremediation and bioaugmentation (BA) for bioremediation of hydrocarbon-contaminated soils. Bacterial isolates obtained from hydrocarbon contaminated soil were screened for rhamnolipid production and isolate BS18, identified as Shewanella seohaensis, was selected for bioremediation experiments. Growth of BS18 in mineral salt medium (MSM) with diesel oil as the carbon source showed a maximum biomass of 8.2 g L−1, rhamnolipid production of 2.2 mg g−1 cell dry weight, surface tension reduction of 28.6 mN/m and emulsification potential (EI24%) of 65.6. Characterization of rhamnolipid based on Fourier transmittance infrared (FTIR) analysis confirmed the presence of OH, CH2/CH3, C=O, and COO stretching vibrations, respectively, which are distinctive features of rhamnolipid type BSs. In bioremediation experiments, the lowest hydrocarbon concentration of 2.1 mg g−1 of soil for non-sterilized soil and 4.3 mg g−1 of soil for sterilized soil was recorded in the combined application of rhamnolipid, phytoremediation, and BA. This treatment also yielded the highest hydrocarbon degrading bacterial population (6.4 Log Cfu g−1 of soil), highest plant biomass (8.3 g dry weight plant−1), and the highest hydrocarbon uptake (512.3 mg Kg−1 of plant).