This info from a favorite blog:
"The hyphae of these fungi synthesize glomalin as part of their stress response. They coat their outer surface with the protein to make a protective waxy coat that keeps the water and nutrients inside the cells. The glomalin coating also makes the fungal strings sticky so they bind soil particles, thus creating an protective ‘armor’ against environmental insults and microbial predators. Most importantly, the fungal “string bags” make soil aggregates."
http://schaechter.asmblog.org/schaechter/2013/05/little-known-glomalin-a-key-...
"Glomalin is a glycoprotein produced abundantly on hyphae and spores of arbuscular mycorrhizal (AM) fungi in soil and in roots. Glomalin was discovered in 1996 by Sara F. Wright, a scientist at the USDA Agricultural Research Service. The name comes from Glomales, an order of fungi.
The chemistry of glomalin-related soil protein (GRSP) is not yet fully understood, and the link between glomalin, GRSP, and arbuscular mycorrhizal fungi is not yet clear. The physiological function of glomalin in fungi is also a topic of current research."
http://en.wikipedia.org/wiki/Glomalin