Kai Sun,Dan Hong,Jie Liu,Abdul Latif,Shunyao Li,Gang Chu,Wenxiu Qin,Youbin Si
The potential application of fungal laccase-assisted bioremediation for estrogen elimination has caused tremendous attention. Herein, naturally-occurring Trametes versicolor laccase ( Tv lac) was capable of significantly removing 17 β -estradiol (E2) and 17 α -ethynylestradiol (EE2) at pH 5. A lower (or higher) pH caused decline in the velocity constants ( k prcs ) by obstructing the single-electron oxidation of estrogen at Tv lac T1-Cu site (or intercepting the intramolecular-electron transfer between Tv lac T1-Cu and T2/T3-Cu sites). Humic acid (HA) and natural phenolic compounds (PCs) are omnipresent in water and can influence the conversion kinetics of estrogen in Tv lac-triggered reactions. Compared with HA-free, the k prcs values of E2 and EE2 in presence of HA respectively reduced 58.61%–83.72% and 69.72%–95.62% at different pH levels. Additionally, the k prcs values for estrogen were also hampered obviously by O -dihydroxyphenol structure of model PCs, owning to the created monomeric/polymeric O -quinones inverted estrogen phenoxy radicals. The generated carbon‑carbon/oxygen self-linking aggregates during Tv lac-mediated estrogen oxidative coupling were characterized, and the polymerization mechanisms were speculated. A fluid-bed reactor with cross-linked-entrapped Tv lac in Ca-alginate beads was established to treat E2 and EE2, respectively. Compared with free Tv lac, immobilized Tv lac prominently exhibited a higher pH and temperature stability. Especially, the fluid-bed reactor with immobilized Tv lac could be reused, keeping its high conversion efficiencies of E2 and EE2 in natural water, only changing from 99.2% to 73.6% and from 98.5% to 70.9% after 1 to 5 cycles, respectively. These findings present an alternative immobilized fungal laccase-based clean biotechnology for continuously handling estrogen-contaminated waterbodies at a large-scale.
Xuemin Qi,Ziyan Niu,Shenghua Xiao,Michael Gatheru Waigi,Hui Lin,Kai Sun
Global-scale crop contamination with environmental estrogens has posed a huge risk to agri-food safety and human health. Laccase is regarded as an unexceptionable biocatalyst for regulating pollution and expediting humification, but the knowledge of estrogen bioremediation and C storage strengthened by laccase-driven rhizosphere humification (LDRH) remains largely unknown. Herein, a greenhouse microcosm was performed to explore the migration and fate of 17 β -estradiol (E2) in water-wheat ( Triticum aestivum L.) matrices by LDRH. Compared to the non-added laccase, the pseudo-first-order decay rate constants of E2 in the rhizosphere solution after 10 and 50 μM exposures by LDRH increased from 0.03 and 0.02 h −1 to 0.36 and 0.09 h −1 , respectively. Furthermore, LDRH conferred higher yield, polymerizability, O-containing groups, and functional-C signals in the humified precipitates, because it accelerated the formation of highly complex precipitates by radical-controlled continuous polymerization. In particular, not only did LDRH mitigate the phytotoxicity of E2, but it also diminished the metabolic load of E2 in wheat tissues. This was attributed to the rapid attenuation of E2 in the rhizosphere solution during LDRH, which limited E2 uptake and accumulation in each subcellular fraction of the wheat roots and shoots. Although several typical intermediate products such as estrone, estriol, and E2 oligomers were detected in roots, only small-molecule species were found in shoots, evidencing that the polymeric products of E2 were unable to be translocated acropetally due to the vast hydrophobicity and biounavailability. For the first time, our study highlights a novel, eco-friendly, and sustainable candidate for increasing the low-C treatment of organics in rhizosphere microenvironments and alleviating the potential risks of estrogenic contaminants in agroenvironments.
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