Glomalin is a

glycoprotein Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycos ...

produced abundantly on

hyphae A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

and

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s of arbuscular

mycorrhizal A mycorrhiza (from Greek μύκης ', "fungus", and ῥίζα ', "root"; pl. mycorrhizae, mycorrhiza or mycorrhizas) is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plan ...

(AM)

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

and in

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...

s. Glomalin was discovered in 1996 by Sara F. Wright, a scientist at the

USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...

Agricultural Research Service The Agricultural Research Service (ARS) is the principal in-house research agency of the United States Department of Agriculture (USDA). ARS is one of four agencies in USDA's Research, Education and Economics mission area. ARS is charged with ext ...

. The name comes from

Glomerales Glomerales is an order of symbiotic fungi within the phylum Glomeromycota. Biology These fungi are all biotrophic mutualists. Most employ the arbuscular mycorrhizal method of nutrient exchange with plants. They produce large (.1-.5mm) spores ...

, an order of fungi. Most AM fungi are of the division

Glomeromycota Glomeromycota (often referred to as glomeromycetes, as they include only one class, Glomeromycetes) are one of eight currently recognized divisions within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycot ...

. An elusive substance, it is mostly known from its glue-like effect on soil and has not yet been isolated.

Definition and controversy

The specific protein glomalin has not yet been isolated and described. What has been described is an extraction process involving heat and citrate, producing mixture containing a substance that is reactive to a

monoclonal antibody A monoclonal antibody (mAb, more rarely called moAb) is an antibody produced from a cell Lineage made by cloning a unique white blood cell. All subsequent antibodies derived this way trace back to a unique parent cell. Monoclonal antibodies ca ...

Mab32B11 raised against crushed AM fungi spores. The substance is then provisionally named "glomalin". As many laboratories do not have the equipment to perform an antibody-based isolation (

ELISA The enzyme-linked immunosorbent assay (ELISA) (, ) is a commonly used analytical biochemistry assay, first described by Eva Engvall and Peter Perlmann in 1971. The assay uses a solid-phase type of enzyme immunoassay (EIA) to detect the presence ...

), a crude mixture called glomalin-related soil proteins (GRSP) is used to refer to the extract portion reactive to the

Bradford protein assay The Bradford protein assay was developed by Marion M. Bradford in 1976. It is a quick and accurate spectroscopic analytical procedure used to measure the concentration of protein in a solution. The reaction is dependent on the amino acid composit ...

. There is significant confusion between the ideal glomalin protein, the antibody-reactive extract portion termed "glomalin", and GRSP. "Glomalin" was first identified by the Mab32B11 assay in 1987. It eluded extraction until 1996 because, according to its discoverer 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 for GRSP was proven to co-extract

humic substances Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th ...

, so it is still not clear if this "glue effect" comes from glomalin or the other substances that are co-extracted using that method.

Description

Based on her extraction, 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." Sampled GRSP takes 7–42 years to biodegrade and is thought to contribute up to 30 percent of the soil carbon where mycorrhizal fungi is present. The highest levels of GRSP were found in volcanic soils of Hawaii and Japan. There is other circumstantial evidence to show that glomalin is of AM fungal origin. When AM fungi are eliminated from soil through incubation of soil without host plants, the concentration of GRSP declines. A similar decline in GRSP has also been observed in incubated soils from forested, afforested, and agricultural land and grasslands treated with fungicide. Concentrations of glomalin in soil are correlated with the

primary productivity In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through c ...

of an

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

. The chemistry of GRSP is not yet fully understood, and the link between glomalin, GRSP, and AM fungi is not yet clear. The

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

function of glomalin in fungi is also a topic of current research.

Effects

GRSPs, along with humic acid, are a significant component of

soil organic matter Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous b ...

and act to bind mineral particles together, improving soil quality. Glomalin has been investigated for its

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

and

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

storing properties, including as a potential method of

carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...

. Glomalin is hypothesized to improve

soil aggregate stability Soil aggregate stability is a measure of the ability of soil aggregates— soil particles that bind together—to resist breaking apart when exposed to external forces such as water erosion and wind erosion, shrinking and swelling processes, and ...

and decrease

soil erosion Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, and ...

. A strong correlation has been found between GRSP and soil aggregate water stability in a wide variety of soils where organic material is the main binding agent, although the mechanism is not known.

References

{{reflist, refs= {{cite journal, url=http://www.ars.usda.gov/is/AR/archive/sep02/soil0902.htm, title=Glomalin: Hiding Place for a Third of the World's Stored Soil Carbon, date=September 2002, first=Don, last=Comis, journal=Agricultural Research, pages=4–7 {{cite journal, url=http://www.ars.usda.gov/is/AR/archive/oct97/glomalin1097.htm, title=Glomalin—Soil's Superglue, date=October 1997, first=Don, last=Comis, journal=Agricultural Research, page=23 {{cite journal, first1=Adam W., last1=Gillespie, first2=Richard E. , last2=Farrell, first3=Fran L., last3=Walley, first4=Andrew R.S., last4=Ross, first5=Peter, last5=Leinweber, first6=Kai-Uwe, last6=Eckhardt, first7=Tom Z., last7=Regier, first8=Robert I.R., last8=Blyth, title=Glomalin-related soil protein contains non-mycorrhizal-related heat-stable proteins, lipids and humic materials, journal=Soil Biology and Biochemistry, volume=43, number=4, date=April 2011, pages=766–777, issn=0038-0717, doi=10.1016/j.soilbio.2010.12.010 {{cite journal, author=Rillig, M., Ramsey, P., Morris, S., Paul, E., year= 2003, title= Glomalin, an arbuscular-mycorrhizal fungal soil protein, responds to land-use change, journal= Plant and Soil , volume=253, pages= 293–299, doi= 10.1023/A:1024807820579, issue=2, s2cid= 11007821 {{cite journal, last=Rillig, first=M. C., year=2004, title=Arbuscular mycorrhizae, glomalin, and soil aggregation, journal=Canadian Journal of Soil Science, volume=84, number=4, pages=355–363, doi=10.4141/S04-003, citeseerx=10.1.1.319.347 {{cite journal, title=Glomalin in Ecosystems, first1=Kathleen K., last1=Treseder, author1-link= Kathleen Treseder , first2=Katie M., last2=Turner, journal=Soil Science Society of America Journal, date=July–August 2007, doi=10.2136/sssaj2006.0377, bibcode=2007SSASJ..71.1257T, volume=71, number=4, pages=1257–1266, url=https://www.soils.org/publications/sssaj/articles/71/4/1257 {{cite journal, first=Gary M., last=King, title=Enhancing soil carbon storage for carbon remediation: potential contributions and constraints by microbes, journal=Trends in Microbiology, volume=19, number=2, date=February 2011, pages=75–84, issn=0966-842X, doi=10.1016/j.tim.2010.11.006, pmid=21167717 {{cite journal, first1=Sonia, last1=Purin, first2=Matthias C., last2=Rillig, title=The arbuscular mycorrhizal fungal protein glomalin: Limitations, progress, and a new hypothesis for its function, journal=Pedobiologia, volume=51, number=2, date=20 June 2007, pages=123–130, issn=0031-4056, doi=10.1016/j.pedobi.2007.03.002 Glycoproteins Soil biology Soil chemistry Fungal proteins

Definition and controversy

Description

Effects

See also

References