Experimental Colonization and Alteration of Orthopyroxene by the Pleomorphic Bacteria Ramlibacter tataouinensis

Abstract

The colonization of orthopyroxene crystals by a pleomorphic bacterium and the mineralogical products resulting from a prolonged interaction have been studied. We used Ramlibacter tataouinensis (strain TTB310), which is an aerobic β-Proteobacterium moving over surfaces by gliding motility and whose life cycle includes rods and spherical cysts. Analysis of cultures grown on solid media with micrometer-sized pyroxene and quartz crystals scattered over the surface revealed a taxis of the bacteria toward the crystals. Given the mineralogical non-specificity of the interaction, a mechanism of elasticotaxis is inferred. After the rods had adhered to the pyroxene surface, they differentiated into cysts leading to the formation of microcolonies that were centered on a crystal grain. This suggests an original coupling between the life cycle of R. tataouinensis and the interaction with the crystals. The alteration of orthopyroxene was studied by high-resolution transmission electron microscopy at the interface between cysts and pyroxene crystals. The pyroxene surface showed an amorphous layer that was more developed than that of abiotic control samples processed under the same conditions. Moreover, chemical analyses showed that the dissolution of pyroxene was reduced in the presence of R. tataouinensis. The origin and the significance of the amorphous layers is discussed.

Keywords:

• bacterial colonization
• bio-alteration
• elasticotaxis
• gliding
• pyroxene
• Ramlibacter tataouinensis
• TEM

This work was supported by the “Géomicrobiologie des environnements extremes, GEOMEX” program grant from the Centre National de la Recherche Scientifique (CNRS). William C. Ghiorse and two anonymous reviewers are acknowledged for detailed and constructive critics about an early version of this work, which led to strong improvements of this paper. We thank Christopher A. Francis for helpful dicussions and corrections brought to the manuscript.

Notes

^a Abbreviations:TSB/10: culture medium; TTB: R. tataouinensis strain; Px: Zimbabwe orthopyroxene whose Fe/Si and Mg/Si ratios determined by electron microprobe are given in the last line of the table; r. #: replicate label.

^b Molar ratios of Fe/Si and Mg/Si released by the dissolution of pyroxene. These ratios were obtained by subtracting the average composition of TSB/10 to the measured compositions in the pyroxene dissolution experiments.

^{c, d, e} Number in parentheses correspond to uncertainties derived from the relative deviations of 5 multiple analyses on each individual sample.