Di-2-ethylhexyl phthalate (DEHP) degradation and microbial community change in mangrove rhizosphere gradients

Di-2-ethylhexyl phthalate (DEHP) is a widespread persistent organic pollutant in the environment. As an ultimate barrier preventing pollutant entry into the ocean, mangrove plays an important role in coastal ecosystem. However, little information is known about DEHP degradation in mangrove rhizosphere. In this study, a rhizobox was used to separate four consecutive rhizosphere compartments with distance of 0-2, 2-4, 4-6, and > 6 mm to the rhizoplane of Kandelia obovata and investigate DEHP gradient degradation behavior in rhizosphere. Sediments closer to the rhizoplane exhibited higher DEHP degradation efficiencies (74.4 % in 0-2 mm layer). More precisely, mangrove rhizosphere promoted the benzoic acid pathway and non-selectively accelerated the production of mono(2-ethylhexyl) phthalate, phthalic acid and benzoic acid. Higher sediment organic matter content, lower pH and less humus in rhizosphere benefited DEHP hydrolysis. In addition, rhizosphere significantly increased microbial biomass and activities comparing to bulk sediments. Some bacterial lineages with potential DEHP degradation capability exhibited a distance-dependent pattern that decreased with the distance to the rhizoplane, including Bacillales, Acidothermaceae, Gammaproteobacteria, and Sphingobacteriales. Our findings suggested that mangrove rhizosphere could accelerate DEHP degradation by altering sediment physicochemical properties and microbial composition, showing positive effects on coastal ecosystem services for eliminating phthalate acid ester contamination.