User:Cynnaco/Glomalin

User:Cynnaco/Glomalin

Lead
"Glomalin is a glycoprotein produced abundantly by hyphae and spores of arbuscular mycorrhizal (AM) fungi found in soil and roots. Glomalin was discovered in 1996 by Sara F. Wright, a scientist at the USDA Agricultural Research Service. The name comes from Glomerales, an order of fungi. Most AM fungi are of the division Glomeromycota. An elusive substance, it is mostly known for its glue-like effect on soil and has not yet been isolated. " Glomalin refers to a protein product of an unknown gene, and the proteins are extracted by autoclaving soil with a sodium citrate process where the extracted proteins are referred to as "glomalin-related soil proteins" or GRSP. This glycoprotein contains asparagine-linked carbohydrate chains, as well as lipids, amino acids, humics, carboxyls, aromatics, and is bound with iron. This glycoprotein has become a recent topic of interest due to its mysterious glue-like quality, apparent significance in maintaining soil quality, resistance to degradation, increased plant stress tolerance, and sequestration of carbon and potentially toxic elements (PTEs).

Discovery and Controversy
Glomalin is an insoluble glycoprotein that requires extreme heat and specific techniques, compared to most glycoproteins, to be extracted from AMF and soils. "Glomalin eluded detection until 1996 because, according to its discover Sarah F. Wright, "It requires an unusual effort to dislodge glomalin for study: a bath in citrate combined with heating at 250 °F (121 °C) for at least an hour... No other soil glue found to date required anything as drastic as this. " However, using advanced analytical methods in 2010, the citrate-heating extraction procedure was proven to co-extract humic substances, so it is still not clear if this "glue effect" comes from glomalin or the other substances that are co-extracted using that method. "

More recently, two-chambered root boxes are the most popular method used in experiments when investigating GRSP's role in soil aggregation, which is the binding of soil particles that contributes to soil structure.

Description
"The specific protein glomalin has not yet been isolated and described. However, glomalin-related soil proteins (GRSP) have been identified using a monoclonal antibody (Mab32B11) raised against crushed AM fungi spores. It is defined by its extraction conditions and reaction with the antibody Mab32B11. " GRSP is also identified by autoclaving from soil, followed by a Bradford assay.

Glomalin is produced by all arbuscular mycorrhizal fungi, where it is bound in spores and hyphae and released into the soil when hyphal turnover occurs, and then decomposition of glomalin releases its nutrients into the soil where they can be taken up by plants. It is still unclear what determines how much GRSP is produced, but different AMF species do produce different amounts of GRSP, which alludes to the belief that GRSP concentrations depend on the AM fungi species and if the species favors greater production while others are more limited.

The entire chemical structure is still not fully known, but the composition of this protein has a range of about 1-8 mg/g protein content, 30-40% carbon, 3-5% nitrogen, 3-4% phosphorus, and 1-9% iron. "Wright thinks the "glomalin molecule is a clump of small glycoproteins with iron and other ions attached... glomalin contains from 1 to 9% tightly bound iron... We've seen glomalin on the outside of hyphae, and we believe this is how the hyphae seal themselves so they can carry water and nutrients. It may also be what gives them the rigidity they need to span the air spaces between soil particles. " Glomalin takes 7–42 years to biodegrade and is thought to contribute up to 30 percent of the soil carbon where mycorrhizal fungi are present. The highest levels of glomalin were found in volcanic soils of Hawaii and Japan, up to 100mg/g. Large amounts of GRSP, 9.3-12.0 mg/g, were found in tropical rainforest soils in Costa Rica, montane rainforests in Mexico, and grasslands. Lower GRSP ranges of 3.87-3.94 mg/g were found in grassland soils in New Zealand. The highest glomalin concentrations are found in surface soils and decrease as depth down the soil profile increases. Generally, a larger presence of GRSP is seen with lower nutrient soils, soils with high C:N ratios, higher microbial activity, and fibrous root systems. Since factors like microbial colonization, nutrients, and established root systems are often determined by land use or certain species presence, like Glomus, then GRSP amounts may also be affected by those factors.

GRSPs have been divided into 3 types, easily extractable GRSP (EE-GRSP), difficulty extractable GRSP (DE-GRSP), and total GRSP (T-GRSP). EE-GSRP is newer, has a higher decomposition rate, and has higher functioning and activity. DE-GRSP is older than EE-GRSP, tightly bound, has a lower decomposition rate, and has stored and less functional fractions. T-GRSP is the sum of both EE-GRSP and DE-GRSP and has often been the main focus of research. In soil, glomalin first appears as EE-GRSP which then experiences natural processes around it, such as hyphal turnover and decomposition, and is converted to DE-GRSP. The newly formed DE-GRSP is then the protein product involved in contributing carbon to the soil and improving the stability of aggregates. To add further to this relationship, more carbon is stored in DE-GRSP compared to EE-GRSP, and inoculating the AM fungi increased the carbon contributed by GRSP, likely due to more hydrolase secretions and more enzyme activity. A positive correlation between T-GRSP and EE-BRSP with soil beta-glucosidase has been shown, as well as a negative correlation between the 2 GRSP types and soil proteases. These correlations lead to the possibility of GRSP contributing to glucose release and maintenance of microbe biomass like beta-glucosidase, and that proteases quickly degrade GRSP.

Effects and Significance
"The chemistry of GRSP is not yet fully understood, and the link between glomalin, GRSP, and AM fungi is still not exactly defined, but many studies have shown correlations between the importance of AM fungi and the presence of GRSP. " The physiological function of glomalin in fungi is also a topic of current research, but GRSP has shown to have roles in many soil processes, although the cause of its glue-like properties is still to be discovered. Despite the unknowns behind the function of GRSP, results have consistently shown that a relationship between GRSP, SOC, and soil aggregates exists, usually with all three factors increasing or decreasing with each other.

The most notable role of glomalin is associated with is its ability to improve and restore the physical properties of soil. It acts as a hydrophobic glue that allows the binding of soil components during aggregation. Larger pools of EE-GRSP, DE-GRSP, and T-GRSP are found with growing ages of sites, which is accordant with more vegetation. As mycorrhizal fungi colonize more area with time, this correlates with an increase in GRSP presence, and since greater colonization allows larger AM fungi networks, this leads to higher GRSP concentrations throughout the soil. Peach trees inoculated with AM fungi saw greater aggregation and less harmful chemicals due to secreted GRSP that binds soil particles together to better soil quality for plants and assimilation and removal of harmful toxins that cause plant disease.

It also plays a significant role in sequestering soil organic carbon (SOC), as well as heavy metals like copper, lead, and cadmium. In vitro studies have shown that glomalin does sequester Cu, and even after precipitation, some Cu remained bound in the glycoprotein, likely due to cell wall interactions between carboxyl, hydroxyl, and amino groups in the fungal wall that act as binding sites for Cu ions in metals. When glomalin is treated with hydrochloric acid, Cu displayed some type of weak association when released from glomalin, which demonstrates that this interaction likely occurs because of ionic exchanges. In high-stress environments, such as high levels of heavy metals, AM fungi produce more GRSP that bind the heavy metals and protect plants from metal toxicity. However, purified glomalin takes up more metals than glomalin taken directly from the soil, which may mean that natural glomalin may not be the best at sequestering metals as purified glomalin that have more open binding spots due to HCl treatments. GRSP also shows the ability to sequester arsenic, as seen in aquatic mangrove systems. Along with improving soil quality by binding and removing pollutants from open soils, GRSP can improve water quality by binding up arsenic in suspended soils and placing them in sediments, which hints at GRSP suspended in water possessing better metal sequestration abilities than soil GRSP.

Due to its long life in the soil, up to 42 years, and its binding properties, GRSP act's as storage and prevents carbon decomposition. Glomalin also contributes to soil nitrogen since it is an N-linked glycoprotein.

Disturbed lands contain lower amounts of GRSP and SOC when compared to untouched lands, and lower amounts of AM fungi spores are seen as well. Cultivation of soils and agricultural processes impact soils by decreasing the porosity of soils, increasing bulk density, and decreasing the diversity of microbes in soils. Lower microbe diversity would lead to decreased AM fungi abundance and less GRSP produced, up to a 50% decrease in both EE-GRSP and DE-GRSP fractions, and conditions of soils that prevent the colonization of fungi and plants.

Potential Future Uses
Larger GRSP concentrations are associated with higher AM fungi concentrations, so for soils that could benefit from more GRSP presence, introducing more fungal species, like Glomus, may be a viable solution to helping soil aggregation. Once research determines which specific species produce the greatest amounts of GRSP, then adding those fungal species to disturbed environments may also prove to be an efficient solution to pollutants. Depending on what the environment needs, low or high GRSP, species with the desired production rates can be implemented in restoration efforts and agricultural activity. Since GRSP has been shown to bind some heavy metals, incorporating AM fungi in contaminated sites could prove to be beneficial in improving soil health. Since disturbances to soil environments impact glomalin concentrations, the degree and type of changes in concentrations, turnover rates, and water stability could be utilized as an indicator of soil health, AM fungi abundances, and the degree of carbon changes in soils. Like the peach trees inoculated with AM fungi, inoculating plants at risk of experiencing significant harm or disease may also be inoculated with AM fungi and improve plant growth and health because of the activities and side effects of higher glomalin presence.