Effects of dissolved organic matter derived from forest leaf litter on biodegradation of phenanthrene in aqueous phase.

Dissolved organic matter (DOM) released from forest leaf litter is potentially effective for the degradation of polycyclic aromatic hydrocarbons (PAHs), yet the inherent mechanism remains insufficiently elucidated. In this study, we investigated the effects of DOM derived from Pinus elliottii and Schima superba leaf litter on the degradation of phenanthrene by the phenanthrene degrading bacterium Sphingobium sp. Phe-1. DOM from different origins and at a large range of concentrations enhanced the degradation rate of phenanthrene. DOM derived from P. elliottii leaf litter decomposed for 12 months used at a concentration of 100mg/L yielded the highest degradation rate (16.9% in 36h) and shortened the degradation time from 48h to 24h. Changes in the composition of DOM during degradation as measured by EEMs-FRI showed that proteins and tyrosine in the DOM supplied readily available nutrients that stimulated biological activity of Phe-1, increasing its growth rate and catechol 2,3-dioxygenase activity. Simultaneously, fulvic acid and humic acid in the DOM enhanced phenanthrene bioavailability by increasing the solubility and mass transfer of phenanthrene, enhancing the uptake kinetics of Phe-1, and increasing the bacteria's direct access to DOM-associated phenanthrene. Humic acid was co-metabolized by Phe-1, resulting in further stimulation of phenanthrene degradation.