Evaluation of bacterial biodegradation and accumulation of phenanthrene in the presence of humic acid.

This study evaluated the effect of humic acid (HA) on physicochemical properties of bacterial surfaces and on mass transfer of polycyclic aromatic hydrocarbons (PAHs) from aqueous phase into intracellular bacteria. Due to this process' potential for bacterial degradation, using Sphingobium sp. PHE3, degradation of phenanthrene (PHE) was compared in HA and non-HA sets. The results showed that approximately 51.1% of PHE at a concentration of 102.0 mg L was biodegraded in the non-HA sets, whereas almost all PHE was biodegraded with HA after 72 h. Interestingly, PHE that accumulated in the intracellular bacteria reached 3.80 mg L for the HA sets, which was significantly higher than that of non-HA. Lipid inclusion bodies appeared when Sphingobium sp. PHE3 was treated with HA. The results were further confirmed by the enhanced bacterial surface sorption capacity for the HA sets. Therefore, we concluded that added HA not only act as carriers and biosurfactants facilitating PHE uptake but also adjust bacteria cell wall properties for internalizing PHE, which ultimately overcame the PHE bioavailability resulting in enhanced biodegradation.