Uptake of Barium from Vermiculite by the Bacterium Pseudomonas fluorescens - New Indications for Barium as a Palaeoproxy

The apparent association of biogenic barite (BaSO4) and organic matter in marine sediments has given support to the idea of using Ba as a proxy for palaeoproductivity. Despite this general acceptance only a few unicellular organisms (acantharian, diatoms) are known to incorporate barium. In this work, we show that the bacterium Pseudomonas fluorescens is able to take up barium. Because natural seawater harbors numerous bacteria many of which may take up Ba, this uptake of Ba explains why it may be considered a palaeoproxy. The introduction of this article reviews briefly what is known to date of Ba as a palaeoproxy, and what is known about bacterial interaction with Ba. Like other trace elements such as Fe, Mn and Sr, Ba can be extracted from vermiculite by Pseudomonas fluorescens and some mutants derived from it. Barium, therefore, seems to be as important a factor in bacterial metabolism as iron or other trace elements. The incorporation of Ba by living bacterial cells in the marine environment and its release from these cells upon their death and subsequent decay can contribute to Ba accumulation in marine sediments.