Mechanism Of The Effect Of Biosurfactants On The Biodegradation Of Phenanthrene By Bacterial Strain GY2B And F14

Surfactant played an important role of the migration,transformation and biodegradation of PAHs and most studies focused on the interactions between chemosynthesis surfactants and PAHs.At present,biosurfactants got more attention because of the environmental friendliness,but little was known about the interaction of biosurfactants with PAHs and bacterial cells.Therefore,saponin and rhamnolipid were selected to investigate the effects and underlying mechanisms of biosurfactants on biodegradation of phenanthrene by Sphingomonas sp.GY2 B and a fusant strain F14(obtained by protoplast fusion between Sphingomonas sp.GY2 B and Pseudomonas sp.GP3A)and bacterial cell surface properties and membrane fluidity.The main results of the study were as follows:(1)The saponin did not affect the phenanthrene removal efficiency by strain GY2 B and had weak inhibitory effect on strain F14.Low concentration rhamnolipid(below CMC)had no effect on the phenanthrene biodegradation of two both strains but high concentration(above CMC)rhamnolipid caused a lag period in the biodegradation of phenanthrene.But saponin and rhamnolipid were nontoxic and promote the growth of two strains,and the rhamnolipid could be used preferentially which would caused a lag period in the biodegradation.(2)In the phenanthrene biodegradation process,cell responses from bacteria was observed and we found that the bacteria secreted some filamentous materials which would positively affect the uptake of nutrients and promote the uptake of phenanthrene.But filamentous materials decreased when saponin or rhamnolipids was added and testified by the Zeta potential test.The addition of rhamnolipid could increase the Zeta potential of strain GY2 B and it was related to the decrease of filamentous materials,which carried less negative surface charge.This phenomenon may resulted from that rhamnolipid formed the micelle to wrap phenanthrene and isolated the direct contact of cells and phenanthrene.And this mechanisms resulted in that rhamnolipid did not enhanced the membrane fluidity and transmembrane tansport of phenanthrene.(3)The FTIR spectrum of strain GY2 B and F14 showed that carboxyl and hydroxyl groups were present in abundance and these groups may function as proton donors.The addition of rhamnolipids caused the change of these transmittance peaks and affected the degradation efficiency.At the same time,we speculated that rhamnolipids influenced the biodegradation of intermediate,via the analysis of stretching vibration of the groups –COOH,which testified by test of the content of intermediate.