Mechanism of rhamnolipid promoting the degradation of polycyclic aromatic hydrocarbons by gram-positive bacteria—Enhance transmembrane transport and electron transfer

Abstract

In this study, the Gram-positive bacterium Bacillus licheniformis T5 was utilized to investigate the impact of rhamnolipid on cell membrane and cell wall, as well as enzyme activity and electron transfer rate within cells. Results indicated that at the optimal concentration of rhamnolipid (200 mg/L), the cell membrane protein and cell wall peptidoglycan content of T5 decreased significantly. Infrared spectrum analysis and ultrastructure observations confirmed these findings, revealing noticeable changes in cell morphology in the presence of rhamnolipid. Specifically, cell folds increased, cell wall texture loosened, thickness decreased sharply, transmembrane channels appeared, and the plasma wall slightly separated. These alterations likely contributed to the increased permeability of the cell membrane. Furthermore, rhamnolipid accelerated the electron transfer rate in T5 cells, enhancing oxidoreductase activity. This study elucidates the mechanism through which rhamnolipid promotes the degradation of polycyclic aromatic hydrocarbons by Gram-positive bacteria, focusing on transmembrane transport and catalytic metabolism.