Precipitation of carbonates by Deleya halophila in liquid media: Pedological Implications in saline soils

Abstract

We investigated the precipitation of carbonates by Deleya halophila in liquid culture media containing different concentrations of marine salt: 2.5%, 7.5%, 12.5%, and 20% (wt/vol). The microorganism was isolated from soils classified as haplic Solonchaks located in arid southeastern Spain. The mineral phases that were precipitated include aragonite, magnesium calcite, and monohydrocalcite in varying proportions depending on the salt concentration. In media containing 2.5% salt, the precipitate consisted of 100% aragonite; with 20% salt, the precipitate was 51% aragonite, 20% monohydrocalcite, and 29% magnesium calcite. Intermediate values were obtained with the middle two salt concentrations. The amount of magnesium in the formula for the precipitated magnesium calcites increased with salinity (0.16 atoms at 7.5% salt, 0.31 atoms at 12.5% salt, 0.32 atoms at 20% salt). The biomineralized formations gave rise to spherulites ranging in diameter from 20 to 500 μm depending on the salinity. The major morphological features were signs of bacterial bodies and zonation effects. The spatial distribution of the different mineral phases within the bioliths awaits further study. We discuss whether this microorganism plays an active role in the precipitation, and we suggest the hypothesis that it may contribute to carbonate precipitation in the soil from which it was isolated.