EXTRACTION OF AN ABUNDANT AND UNUSUAL PROTEIN FROM SOIL AND COMPARISON WITH HYPHAL PROTEIN OF ARBUSCULAR MYCORRHIZAL FUNGI

It has been speculated that arbuscular mycorrhizal fungi (AMF) produce extracellular compounds and that these are involved in soil stabiliza tion, An unusual and abundant protein was found on hyphae of AMF, and it was hypothesized that the hyphal protein could be found in soil, Th e purpose of this work was to test extraction conditions for soil prot ein on a range of soils collected from undisturbed sites, to compare p rotein from hyphae with protein from soils, and to examine the relatio nship between soil protein and percent of total dry weight of soil mad e up of ca. 1 to 2-mm water stable aggregates. The A-horizons of 12 ac idic soils collected from the midAtlantic area of the United States we re used to develop a protocol for protein extraction, Protein was meas ured by the Bradford assay, with bovine serum albumin as the standard, Also, an indirect enzyme-linked immunosorbent assay (ELISA), using th e monoclonal antibody that had been used to detect the protein on hyph ae of AMF, was performed on 0.5 mu g of protein from soil or hyphae, S odium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of denatured protein was used to compare soil protein with hyphal protei n,The extraction conditions that gave the best results for total prote in were 0.25 g soil in 2 mL of 50 mM citrate, pH 8.0, for 90 min at 12 1 degrees C yielding a range of 4.4 to 14.4 mg protein/g of soil for t hese soils, Highest ELISA values were obtained by using 20 mM citrate, pH 7.0, for 30 min at 121 degrees C, but less protein was extracted u nder these conditions, Crude extracts of protein from hyphae and soil showed the same banding patterns and density of bands on SDS-PAGE gels . ELISA values for soils were between 60 and 107% of hyphal ELISA valu es. Total protein concentration was correlated linearly with organic c arbon in soil (r(2) = 0.85, P less than or equal to 0.001),The percent dry weight of soil composed of water-stable aggregates was correlated positively (P less than or equal to 0.05) with silt and ELISA values and correlated negatively with sand, The possible contribution of this protein to soil stabilization is discussed.