Accelerated biodegradation of p-tert-butylphenol in the Phragmites australis rhizosphere by phenolic root exudates

Abstract

Phenolic root exudates (PREs) released from plants are potentially effective for the degradation of aromatic compounds, yet the inherent process and mechanism remain insufficiently elucidated. In this study, we selected four representative PREs of P. australis, namely p-hydroxybenzoic acid (PHA), p-coumaric acid (PCA), caffeic acid (CA), and ferulic acid (FA), to investigate the accelerated biodegradation of p-tert-butylphenol (PTBP) by PREs in the rhizosphere and their mechanisms. The results showed that PTBP was initially adsorbed to root surface, and subsequently degraded by rhizosphere microbes of P. australis. The presence of PHA, PCA, and FA was beneficial for the enrichment of PTBP-degrading bacteria and the decomposition of PTBP, particularly PCA. Although CA was also favorable to microbial accumulation, it had no effect on PTBP degradation. This is possibly because PHA, PCA, and FA with monohydroxy structure similar like PTBP may promote the microbes for releasing hydroxylase to catalyze the phenolic ring hydroxylation followed by a cleavage pathway, whereas CA with ortho-dihydroxy structure cannot act on this reaction. Collectively, our data suggest PREs can accelerate biodegradation of specific aromatic compounds (e.g. PTBP) via co-metabolism in the rhizosphere of plants, according to their functional structures.