The Effects Of Paenibacillus Sp.Strain SB-6 On Weathering Of 2:1 Type Clay Minerals And Its Mechanism

The transformation of clay minerals reflects the formation process of soil on the whole.Therefore,research on the weathering process of clay minerals and its products contributes to have a profound understanding of the formation of soil,the evolution of the earth's ecosystem,and the circulation of elemental geochemistry.Studies have demonstrated that microbes cannot only promote the weathering rate,but also accelerate the transformation of minerals,even form new minerals.Taking into account of the vital significances above,we chose three kinds of 2:1 type clay minerals which are typical in the soil as materials-vermiculite,montmorillonite and illite,with a strain of Paenibacillus sp.,which is commonly in the soil,through a series of interaction experiments between clay minerals and bacterium to probe into the adsorption and the effect of its secretion by strain SB-6.This paper was endeavouring to illustrate the weathering mechanism of clay minerals under the action of bacterium.In this paper,the mainly results are as follows:?1?Strain SB-6 of Paenibacillus sp.can accelerate the weathering of clay minerals,specifically:the cationic concentration in the solution of mineral-bacterium are significantly higher than that of the abiotic experiment;The crystallinity?V/P?of vermiculite and montmorillonite presented a downward trend,the Non-symmetry index?Ns?and the ratio of diffraction peak?I001/I003?both on the rise,these indicated that the crystallinity of clay minerals became lower;New minerals have formed during the weathering process of montmorillonite and illite.There are no changes in the control experiment.?2?Based on the analysis of the change of mianeral structure and the formation of new minerals,there exist the following sequence on clay minerals:montmorillonite?illite?halloysite.?3?The weathering results showed that the proportion of vermiculite in the structure of phlogopite/vermiculite mixed-layer did not demonstrate a significantly change.Part of montmorillonite transformed into illite,during the late stage of the experiments?when pH was higher than 6,after 50 days?,the Ca²⁺ released from montmorillonite combined with the carbonate ion from metabolism eventually precipitated as calcite.During the late stage of illite weathering,we have halloysite and calcite in the weathering remnants.?4?Releasing of the low molecular weight organic acids?LMWOAs?from the bacterium,promoting the release of elements from the interlayer and crystal lattice by acidolysis and complexation.Releasing of exopolysaccharides?EPS?,has no obvious role in promoting,but maybe serving as a heterogeneous nucleation template for the formation of carbonate minerals.?5?Clay minerals have an evident effect on strain SB-6 about its physiological characteristics.With different minerals,the bacterial metabolites have obvious difference on types and concentrations.The physiological characteristics of bacteria related to the species of mineral.?6?In the presence of strain SB-6 of Paenibacillus sp.,the strength of weathering intensity is:montmorillonite>illite>vermiculite.