The Release of Some Elements from Vermiculite during the Short Periods of Incubation by Heterotrophic Bacteria

Microorganisms play an important role in the formation and decomposition of clay minerals. In this research the release of iron, silicon and non-exchangeable potassium from vermiculite owing to heterotrophic bacteria was examined. For this, an experiment was carried out in a completely randomized design at three replications. The experiment factors consisted of bacterial inoculation (control, Pseudomonas sp. Rhizo_9, Enterobacter cloacae Rhizo_33) and incubation period (7, 15, 30, 45 and 60 days). Results showed a significant effect of bacterial inoculation and incubation period on silicon, non-exchangeable potassium and iron release. The most active release of potassium, silicon and iron was recorded at the presence of Enterobactercloacae on the 15, 30 and 45 days after the incubation, respectively. Thin-layer chromatographic analysis of the organic acids in the culture broth of both strains exhibited spots of malic, tartaric and citric acid, produced by Pseudomonas sp. and oxalic, tartaric and unknown acid produced by Enterobactercloacae. The XRD results of mineral decomposition with bacterial treatments indicated converted vermiculite with limited expansion into expansible smectite.