Microbial degradation of phyllosilicates during simulated podzolization

Abstract

Perfusion experiments were conducted to study mechanisms in the transformation of phyllosilicates by oxalic acid and other complexing agents synthesized by microorganisms that survived partial sterilization. Those resistant to thymol were mostly non-pigmented Pseudomonas sp. and Bacillus but included a few yeasts. The organic acids formed by the microorganisms dissolved large amounts of mineral elements from samples of granites and granitic sand. Organo-metal complexes were formed with Fe and Al. 70–100% of the dissolved Fe were in complexes stable over a wide range in pH. 10–30% of the dissolved Fe and Al were in very stable anionic complexes that were not exchangeable with strong cationic resins. The acidic compounds that were formed solubilized appreciable amounts of ferromagnesian minerals, mainly biotite, and destroyed primary chlorite and some vermiculite. Under some experimental conditions, illite-vermiculite was transformed into vermiculite and biotite into vermiculite or into a white and brittle residue of Si and Al. Because similar mineral transformations have been shown to occur during podzolization in the field, our experiments are thought to provide a satisfactory model of weathering in that soil-forming process.