Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 2005
Publication Date: August 1, 2006
Citation: Wright, S.E., Nichols, K.A., Schmidt, W.F. 2006. Comparison of efficacy of three extractants to solubilize glomalin on hyphae and in soil. Chemosphere. 64(7):1219-1224. Interpretive Summary: Glomalin is a large insoluble component of soil organic matter that was not discovered until 10 years ago. Research on glomalin is in its infancy, and information is needed on how extraction conditions affect glomalin recovery and glomalin to be used for further analysis. We tested three different solutions to detect differences in the amount or quality of the glomalin we could extract from two sources. A solution of sodium citrate, the extraction solution used for the past 10 years, was compared with sodium borate or sodium pyrophosphate. The sources of glomalin were hyphae of arbuscular mycorrhizal fungi, the beneficial soil fungi that produce glomalin, and soils from various parts of the U.S. We found that sodium pyrophosphate was slighly better than the other two chemicals tested in solubilizing glomalin on hyphae or from soils. We found that citrate attaches to or is trapped by glomalin. These results indicate that sodium pyrophosphate should be used to solublilize glomalin when the product is to be used for structural analysis and is somewhat better than citrate in extraction efficiency for glomalin in soils. This information will assist researchers who wish to quantify glomalin from soils or hyphae and will be especially relevant to researchers who are interested in extracting glomalin to be used for structural analysis experiments.
Technical Abstract: Glomalin typically is extracted from soil and hyphae using sodium citrate at 121 oC. Four arbuscular mycorrhizal fungi isolates and seven soils were used to test the efficacy of 100 mM (pH 9.0) sodium salts of borate or pyrophosphate compared with 100 mM sodium citrate (pH 9.0) for two 1-h cycles for hyphae and four 1-h cycles for soil at 121 oC. Further extractions of soils were performed to explore for the presence of a recalcitrant glomalin fraction. Comparisons made for hyphal extracts were concentrations of total and immunoreactive protein and 1H NMR spectra. Extracts from soils were compared using values for percentage carbon, carbon weight, gravimetric weight, Bradford total protein, immunoreactive total protein and 1H NMR spectra. No differences in hyphal protein values were detected for the various extractants. Comparisons among soil extracts indicated that pyrophosphate was the most effective extractant for the first four 1-h cycles because 13% of the total protein was in a recalcitrant pool compared with 32% when either borate or citrate was used. Citrate was attached to or was trapped by glomalin extracted from hyphae and soil when citrate was used at any stage of the extraction procedure as revealed by 1H NMR. There was no indication that borate and pyrophosphate were similarly attached. Differences were not detected among total values for glomalin percentage carbon, carbon weights, gravimetric weights and total protein for the different extractants, indicating that only a small amount of citrate attached to or was trapped by glomalin.