Exolaccase-boosted humification for agricultural applications

Laccase-induced decontamination and humification mechanisms of estrogen in water-crop matrices

Enzymatic humification plays a crucial biogeochemical role in eliminating steroidal estrogens and expanding organic carbon stocks. Estrogenic contaminants in agroecosystems can be taken up and acropetally translocated by crops, but the roles of laccase-triggered rhizospheric humification (L-TRH) in pollutant dissipation and plant uptake remain poorly understood. In this study, the laccase-induced decontamination and humification mechanisms of 17β-estradiol (E2) in water-crop media were investigated by performing greenhouse pot experiments with maize seedlings (Zea mays L.). The results demonstrated that L-TRH effectively dissipated E2 in the rhizosphere solution and achieved the kinetic constants of E2 dissipation at 10 and 50 μM by 8.05 and 2.75 times as much as the treatments without laccase addition, respectively. The copolymerization of E2 and root exudates (i.e. phenols and amino acids) consolidated by L-TRH produced a larger amount of humified precipitates with the richly functional carbon architectures. The growth parameters and photosynthetic pigment levels of maize seedlings were greatly impeded after a 120-h exposure to 50 μM E2, but L-TRH motivated the detoxication process and thus mitigated the phytotoxicity and bioavailability of E2. The tested E2 contents in the maize tissues initially increased sharply with the cultivation time but decreased steadily. Compared with the treatment without laccase addition, the uptake and accumulation of E2 in the maize tissues were obviously diminished by L-TRH. E2 oligomers such as dimer, trimer, and tetramer recognized in the rhizosphere solution were also detected in the root tissues but not in the shoots, demonstrating that the acropetal translocation of E2 oligomers was interrupted. These results highlight a promising strategy for decontaminating estrogenic pollutants, boosting rhizospheric humification, and realizing low-carbon emissions, which would be beneficial for agroenvironmental bioremediation and sustainability.

Novel insights into the mechanism of laccase-driven rhizosphere humification for alleviating wheat 17β-estradiol contamination

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 17β-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.

Waste milk humification product can be used as a slow release nano-fertilizer

The demand for milk has increased globally, accompanied by an increase in waste milk. Here, we provide an artificial humification technology to recycle waste milk into an agricultural nano-fertilizer. We use KOH-activated persulfate to convert waste milk into fulvic-like acid and humic-like acid. We mix the product with attapulgite to obtain a slow-release nano fulvic-like acid fertilizer. We apply this nano-fertilizer to chickweeds growing in pots, resulting in improved yield and root elongation. These results indicate that waste milk could be recycled for agricultural purposes, however, this nano-fertilizer needs to be tested further in field experiments.

Lignin precursors enhance exolaccase-started humification of bisphenol A to form functional polymers

Humification plays a significant role in converting phenolic pollutants and forming heterogeneous polymers, but few studies have been performed to investigate exolaccase-started humification (ESH). Herein, the influences of lignin precursors (LPs) on exolaccase-induced bisphenol A (BPA) removal and humification were explored. In particular, the architectural features and botanical effects of the formed humification products were also tested. ESH was extremely beneficial in boosting BPA removal in the presence of LPs. Compared with LP-free (58.49%), 100% of BPA was eliminated after the reaction with ESH for 72 h. Such a process was controlled by an exolaccase-caused random assembly of radicals, which generated a large number of hydrophobic polymers through nonspecific covalent binding of C-C and/or C-O. These humified polymers were extremely stable at pH 2.0-10.0 and -20 °C to 80 °C and displayed unique functions, i.e., scavenged 2,2-diphenyl-1-picrylhydrazyl/2,2'-azino-bis3-ethylbenzothiazoline-6-sulphonic acid radicals and exerted antioxidant capacities. More importantly, the functional polymers could act as auxin analogs to increase the germination index (>100%), plant biomass, and salt tolerance of radish seedlings. Our findings disclosed that ESH could not only be optimized to mitigate the ecological risks of phenolic pollutants and sequester organic carbon in environmental bioremediation, but the resulting abundant auxin analogs also contributed to agricultural productivity.

Exolaccase Propels Humification to Decontaminate Bisphenol A and Create Humic-like Biostimulants

Exolaccase-propelled humification (E-PH) helps eliminate phenolic pollutants and produce macromolecular precipitates. Herein, we investigated the influencing mechanism of 12 humic precursors (HPs) on exolaccase-enabled bisphenol A (BPA) decontamination and humification. Catechol, vanillic acid, caffeic acid, and gentian acid not only expedited BPA removal but also created large amounts of copolymeric precipitates. These precipitates had rich functional groups similar to natural humic substances, which presented great aromatic and acidic characteristics. The releasing amounts of BPA monomer from four precipitates were 0.08-12.87% at pH 2.0-11.0, suggesting that BPA-HP copolymers had pH stability. More excitingly, certain copolymeric precipitates could stimulate the growth and development of radish seedlings. The radish growth-promotion mechanisms of copolymers were involved in two aspects: (1) Copolymers interacted with root exudates to accelerate nutrient uptake; (2) Copolymers released auxins to provoke radish growth. These results may provide an innovative strategy for decontaminating phenolic pollutants and yielding humic-like biostimulants in E-PH.

One stone, two birds: A Cu-S cluster as a laccase-mimicking nanozyme and sulfite activator for phenol remediation in marine environments

Phenols are infamous pollutants in marine environments and present a grave danger to human health, which makes their efficient detection and removal serious issues. Colorimetry is a simple method for detecting phenols in water because phenols can be oxidized by natural laccase and generate a brown product. However, high cost and poor stability impede the wide-spread implementation of natural laccase in phenol detection. To reverse this adverse situation, a nanoscale Cu-S cluster, Cu₄(MPPM)₄ (Cu₄S₄, MPPM = 2-mercapto-5-n-propylpyrimidine), is synthesized. As a stable and inexpensive nanozyme, Cu₄S₄ shows excellent laccase-mimicking activity and prompts the oxidation of phenols. This characteristic makes Cu₄S₄ a perfect option for phenol detection with colorimetry. In addition, Cu₄S₄ also exhibits sulfite activation properties. It can degrade phenols and other pollutants with advanced oxidation processes (AOPs). Theoretical calculations show good laccase-mimicking and sulfite activation properties originating from appropriate interactions between Cu₄S₄ and substrates. We anticipate that the phenol detection and degradation characteristics of Cu₄S₄ make it a promising material to be used for practical phenol remediation in water environments.

Biotransformation of bisphenol A in vivo and in vitro by laccase-producing Trametes hirsuta La-7: Kinetics, products, and mechanisms

Bisphenol A (BPA) is a ubiquitous endocrine disruptor that poses adverse human health risks. Herein, biotransformation kinetics, products, and mechanisms of BPA undergoing a laccase-producing Trametes hirsuta La-7 metabolism were for the first time reported. Strain La-7 could completely biotransform ≤0.5 mmol·L^-1 BPA within 6 d in vivo. Notably, its extracellular crude laccase solution (ECLS) and intracellular homogenized mycelium (HM) only required 6 h to convert 85.71% and 84.24% of 0.5 mmol·L^-1 BPA in vitro, respectively. The removal of BPA was noticeably hampered by adding a cytochrome P-450 inhibitor (piperonyl butoxide) in HM, disclosing that cytochrome P-450 monooxygenase participated in BPA oxidation and metabolism. BPA intermediates were elaborately identified by high-resolution mass spectrometry (HRMS) combined with ¹³C stable isotope ratios (BPA: ¹³C₁₂-BPA = 0.25: 0.25, molar concentration). Based on the accurate molecular mass, isotope labeling difference, and relative intensity ratio of product peaks, 6 versatile metabolic mechanisms of BPA, including polymerization, hydroxylation, dehydration, bond cleavage, dehydrogenation, and carboxylation in vivo and in vitro, were confirmed. Germination index values revealed that inoculating strain La-7 in a BPA-contaminated medium presented no phytotoxicity to the germinated radish (Raphanus sativus L.) seeds. In vivo, Mg²⁺, Fe²⁺, Fe³⁺, and Mn²⁺ were conducive to BPA removal, but Cd²⁺ and Hg²⁺ significantly obstructed BPA elimination. Additionally, strain La-7 also exhibited high-efficiency metabolic ability toward estrone (E1), 17β-estradiol (E2), and 17α-ethinylestradiol (EE2), with more than 96.13%, 96.65%, and 100% of E1, E2, and EE2 having been converted, respectively. Our findings provide an environmentally powerful laccase-producing fungus to decontaminate endocrine disruptor-contaminated water matrices by radical polymerization and oxidative decomposition.