Carbonate and Phosphate Precipitation by Chromohalobacter marismortui

The ability of Chromohalobacter marismortui to precipitate carbonate and phosphate minerals has been demonstrated for the first time. Mineral precipitation in both solid and liquid media at different salts concentrations and different magnesium/calcium ratios occurred whereas crystal formation was not observed in the control. The precipitated minerals were studied by X-ray diffraction, scanning electron microscopy and EDX, and were different in liquid and solid media. In liquid media aragonite, struvite, vaterite and monohydrocalcite were precipitated forming crystals and bioliths. Bioliths accreted preferentially close to organic pellicles, whereas struvite preferentially grows in microenvironments free of such pellicles. Magnesian calcite, calcian-magnesian kutnahorite, “proto-dolomite” and huntite were formed in solid media. The Mg content of the magnesian calcite and of Ca-Mg kutnahorite also varied depending on the salt concentration of the culture media. This is the first report on bacterial precipitation of Ca-Mg kutnahorite and huntite in laboratory cultures. The results of this research show the active role played by C. marismortui in mineral precipitation, and allow us to compare them with those obtained previously using other taxonomic groups of moderately halophilic bacteria.

Keywords:

• biomineralization
• aragonite
• huntite
• Ca-Mg kutnahorite
• magnesian calcite
• monohydrocalcite
• struvite
• vaterite
• C. marismortui

Acknowledgments

We acknowledge A. González-Segura (CIC, Univ. of Granada) for her help along different phases of the SEM laboratory work. We thank the critical reading of two anonymous reviewers for their comments and suggestions. Financial support for this research was provided by the Spanish Project BTE 2001-2852 MEC-CICYT, and by the Research Group No.164 (4089) of the Junta de Andalucía.

Notes

¹ Only analysed the struvite fraction accumulated in the bottom of culture flasks, without bioliths.

² Only analysed the biolith fraction accumulated in pellicles, without struvite crystals.

³ Struvite not determined by PXRD, but optically from crystals accumulated in the bottom of the culture flasks.