Glomalin-related soil protein reduces the sorption of polycyclic aromatic hydrocarbons by soils

Research progress and prospect of glomalin-related soil protein in the remediation of slightly contaminated soil

Soil pollution caused by organic pollutants and potentially toxic elements poses a serious threat to sustainable agricultural development, global food security and human health. Therefore, strategies for reducing soil pollution are urgently required. Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is widely recognized for its ability to remediate slightly-contaminated soil. Glomalin-related soil protein (GRSP) production by AMF is considered a vital mechanism of AMF-assisted phytoremediation. GRSP is widespread in soils and may contribute to the remediation of slightly contaminated soils. GRSP facilitates stabilization of pollutants in soils by interacting with pollutants owing to its abundant functional groups, recalcitrance, and long turnover time. It also enhances soil bioremediation and phytoremediation by stimulating soil microbial activity, improving soil structure, and providing nutrients for plants. However, research on GRSP is still in its early stages, and studies on contaminated soil remediation are limited. The effectiveness of GRSP in situ remediation remains to be proved. This review summarizes current knowledge regarding the GRSP distribution and its contribution to the remediation of slightly contaminated soils. Additionally, we present strategies to increase the GRSP content in contaminated soils, as well as prospects for future studies on the use of GRSP in contaminated soil remediation. This study focuses on recent developments that aim to improve awareness of the role of GRSP in soil remediation and relevant future directions.

Potential interaction mechanisms between PAHs and glomalin related-soil protein (GRSP)

Glomalin-related soil protein (GRSP) has gained widespread attention because of its benefits to carbon sequestration, improving soil quality and fixing heavy metals. However, studies on how GRSP affects the environmental fate of organic contaminants are scarce. In this study, different types of GRSPs were isolated from forest soils and characterized to study the binding of GRSPs and PAHs under different environmental conditions. The results indicated that GRSPs contain abundant functional groups (such as -NH, -COOH, and CO) and material composition, like humic acid, proteins, and lipids. For the tested GRSPs, EE-GRSP has lower DOC, SUVA₂₆₀ and SUVA₂₈₀ values, as well as higher E2/E3 values, indicating that EE-GRSP has lower hydrophobicity and molecular weight. These properties can lead to strong interactions between GRSP and PAHs, especially with benzopyrene, which has a high K_ow and K_sw and a large molecular size, with binding constants ranging from 16,119 to 163,697 L kg^-1. Furthermore, low pH (pH = 3) and temperature (15 °C) could increase GRSP's aggregation, enhance the GRSP binding ability with PAHs, whose binding constants were 11,595 and 5067.3 L kg^-1. Therefore, the binding between GRSP and PAHs may lead to changes in the fate of PAHs in the soil and affect the environmental risk of PAHs. The results presented here will deepen our understanding of the environmental function of GRSPs and provide a theoretical basis to further elucidate the mechanisms of GRSPs and organic pollutants.

Fungal bioproducts for petroleum hydrocarbons and toxic metals remediation: recent advances and emerging technologies

Petroleum hydrocarbons and toxic metals are sources of environmental contamination and are harmful to all ecosystems. Fungi have metabolic and morphological plasticity that turn them into potential prototypes for technological development in biological remediation of these contaminants due to their ability to interact with a specific contaminant and/or produced metabolites. Although fungal bioinoculants producing enzymes, biosurfactants, polymers, pigments and organic acids have potential to be protagonists in mycoremediation of hydrocarbons and toxic metals, they can still be only adjuvants together with bacteria, microalgae, plants or animals in such processes. However, the sudden accelerated development of emerging technologies related to the use of potential fungal bioproducts such as bioinoculants, enzymes and biosurfactants in the remediation of these contaminants, has boosted fungal bioprocesses to achieve higher performance and possible real application. In this review, we explore scientific and technological advances in bioprocesses related to the production and/or application of these potential fungal bioproducts when used in remediation of hydrocarbons and toxic metals from an integral perspective of biotechnological process development. In turn, it sheds light to overcome existing technological limitations or enable new experimental designs in the remediation of these and other emerging contaminants.

Spatial heterogeneity in chemical composition and stability of glomalin-related soil protein in the coastal wetlands

GRSP is widely distributed in coastal wetlands, and there is a tendency for it to degrade with increasing burial depth. However, the dynamic changes in the chemical composition and stability of GRSP during the burial process are still unclear. The purpose of this study is to clarify the chemical composition and accumulation characteristics of GRSP during the burial process in the Zhangjiang estuary. In a field study, soil cores to the depth of 100 cm were collected in the estuary from mangrove forests dominated by Kandelia obovata and Avicennia marina, and from mudflat. The results showed that the concentration of GRSP in mangrove forest soil was significantly higher than that in the mudflat (p < 0.05), and the C/N ratio of GRSP increased with depth at all sites. Analysis of Fourier transform infrared (FTIR) data showed that the degradation rates of the GRSP's compositions varied with increasing burial depth, with microbial action and pH possibly being the main factors affecting degradation. Values of recalcitrance index (RI) showed that the stability of GRSP increased with increasing depth, and the contribution of GRSP to soil organic carbon (SOC) also increased. This suggests that the burial process plays a role in screening and storing the stable components of GRSP. Overall, our findings suggest that the concentration and chemical composition of GRSP vary dynamically according to habitat and burial processes. In addition, the improved stability of GRSP could contribute to carbon sequestration in coastal wetlands.

Contributions of partition and adsorption to polycyclic aromatic hydrocarbons sorption by fractionated soil at different particle sizes

Partition and adsorption of polycyclic aromatic hydrocarbons (PAHs) are critical mechanisms determining their fate at the solid-liquid interface. The complexity of soil composition makes it difficult to distinguish between partition and adsorption, and bates the accuracy of the research results. This study found that the composition and structure of the soil particles (SAs) of varying particle sizes were significantly different. Partition contributed significantly to phenanthrene (Phe) sorption in SAs over 0.002 mm. However, PAHs had the highest sorption coefficient (K_d) in SA less than 0.002 mm (SA-3), and the lower aqueous phase equilibrium concentration of Phe, the greater the adsorption effect. According to morphology and structural analysis, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), interactions of micropores, soil organic matter (SOM) and minerals enhanced the sorption of PAHs. Additionally, thermogravimetry and mass spectrometry (TG-MS) results proved that SOM could inhibit the release of PAHs adsorbed in SAs during heating process. We observed that the Log Koc of PAHs was the most important factor in determining the K_d in SAs applying principal component analyses (PCA), and they have significant linear relationships (R² = 0.79-0.93). These findings provide new understandings on interface reactivity of PAHs sorption to soils and the development of interface model.

Impacts of photoaging on the interactions between graphene oxide and proteins: Mechanisms and biological effect

Graphene oxide (GO) are subjected to photoaging in aquatic environment, and inevitably enter biota and then interact with proteins. Here, the interactions of pristine and photoaged GO with two typical proteins (bovine serum albumin (BSA) and lysozyme) were systematically investigated. Due to long term photoirradiation (1-3 day), the lateral size of GO decreased greatly, and the oxygen-containing groups decreased as well while the graphitic carbon contents increased. Compared to pristine GO, the photoaged GO displayed stronger binding affinities with both proteins, which was mainly attributed to the increased binding sites as a result of smaller lateral size and increased hydrophobicity. The photoaging effect was more obvious for the negatively charged BSA, because hydrogen bonding and van der Waals force were mainly involved in the enthalpy-driven interactions between them. While, the strong electrostatic attraction between the positively charged lysozyme and GO diminished the photoaging effect. Analyses of synchronous, three-dimensional fluorescence spectra and fibrillation experiments intensified that the photoaged GO induced more serious changes in conformational structure of BSA and exhibited stronger inhibition on fibrillation of BSA compared to pristine GO. This study provided novel insights into the increased ecological risks of GO as a result of photoaging.

Release of sediment metals bound by glomalin related soil protein in waterfowls inhabiting mangrove patches

Glomalin-related soil protein (GRSP) has received extensive attention due to its ability to immobilize metals in the environment. However, whether it can enter the food chain through digestion is still unclear. Mangroves occupy the transition zone between the sea and land, have important ecological functions. Mangroves suffer from fragmentation due to human activities and urbanization. A variety of waterfowls inhabit near the mangroves and ingest sediment settled on their food inadvertently or for grit; therefore, they are ideal for revealing GRSP's role in metal enrichment. In this study, we investigated the release of metals from mangrove surface sediments and GRSP through a physiologically based extraction test. The investigated metals (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in sediments and those bound to GRSP would be mainly released in the gizzard phase. GRSP appeared to be an efficient carrier of Cu, Zn, Pb, and As from sediments to the waterfowls via direct sediment ingestion. For instance, 3.21% and 3.34% of sediment Cu were released in the gizzard and intestinal phases, respectively, meanwhile GRSP-bound Cu contributed 5.04% and 5.42% to this flux. The continuum of GRSP enrichment - complexation of GRSP and metals - biological accessibility of GRSP-bound metals, influenced by both direct and indirect effects from major nutrients (e.g., C, N, P, and S) and metal contents (e.g., Cu, Cd, Ni), controlled the release of GRSP-bound metals during simulated digestion. Overall, this study provides new insights into the potential risk of GRSP acting as a metal delivery vehicle in the food chain.