Journal
APPLIED CLAY SCIENCE
Volume 39, Issue 3-4, Pages 142-150Publisher
ELSEVIER
DOI: 10.1016/j.clay.2007.07.006
Keywords
Bacillus thuringiensis; human serum albumin; beta-glucuronidase; Cry3Bb1 protein; montmorillonite; kaolinite; adsorption; binding; microbial degradation; enzyme activity; XRD analysis
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Human serum albumin (HSA), beta-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 +/- 0.21 mu g adsorbed and bound mu g(-1) of M; 2.1 +/- 0.39 mu g adsorbed and bound mu g(- 1) of K. With GUS, 2.2 +/- 0.29 mu g adsorbed and 1.7 +/- 0.21 mu g bound mu g(-1) of M; 1.5 +/- 0.28 mu g adsorbed and 1.0 +/- 0.03 mu g bound mu g(-1) of K. HSA was adsorbed and bound the least: 1.2 +/- 0.04 mu g adsorbed and 0.8 +/- 0.05 mu g bound mu g(-1) of M; 0.4 +/- 0.05 mu g adsorbed and 0.4 +/- 0.03 mu g bound mu g(-1) of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals. (C) 2007 Elsevier B.V. All rights reserved.
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