PRECIPITATION OF CARBONATES BY DELEYA-HALOPHILA IN LIQUID-MEDIA - PEDOLOGICAL IMPLICATIONS IN SALINE SOILS

We investigated the precipitation of carbonates by Deleya halophila in liquid culture media containing different concentrations of marine sa lt: 2.5%, 7.5%, 12.5%, and 20% (wt/vol). The microorganism was isolate d from soils classified as haplic Solonchaks located in arid southeast ern Spain. The mineral phases that were precipitated include aragonite , magnesium calcite, and monohydrocalcite in varying proportions depen ding on the salt concentration. In media containing 2.5% salt, the pre cipitate consisted of 100% aragonite; with 20% salt, the precipitate w as 51% aragonite, 20% monohydrocalcite, and 29% magnesium calcite. Int ermediate values were obtained with the middle two salt concentrations . The amount of magnesium in the formula for the precipitated magnesiu m calcites increased with salinity (0.16 atoms at 7.5% salt, 0.31 atom s at 12.5% salt, 0.32 atoms at 20% salt). The biomineralized formation s gave rise to spherulites ranging in diameter from 20 to 500 mu m dep ending on the salinity. The major morphological features were signs of bacterial bodies and zonation effects. The spatial distribution of th e different mineral phases within the bioliths awaits further study. W e discuss whether this microorganism plays an active role in the preci pitation, and we suggest the hypothesis that it may contribute to carb onate precipitation in the soil from which it was isolated.