Nanobacteria-like calcite single crystals at the surface of the Tataouine meteorite

Abstract

Nanobacteria-like objects evidenced at the surface of the orthopyroxenes of the Tataouine meteorite in South Tunisia have been studied by scanning and transmission electron microscopies. A method of micromanipulation has been developed to ensure that exactly the same objects were studied by both methods. We have shown that the nanobacteria-like objects are spatially correlated with filaments of microorganisms that colonized the surface of the meteoritic pyroxene during its 70 years of residence in the aridic Tataouine soil. Depressions of a few micrometers in depth are observed in the pyroxene below the carbonates, indicating preferential dissolution of the pyroxene and calcite precipitation at these locations. The nanobacteria-like small rods that constitute calcium carbonate rosettes are well crystallized calcite single crystals surrounded by a thin amorphous layer of carbonate composition that smoothes the crystal edges and induces rounded shapes. Those morphologies are unusual for calcite single crystals observed in natural samples. A survey of recent literature suggests that the intervention of organic compounds derived from biological activity is likely in their formation.

Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes?

“…and Khale, 1993;Verrecchia and Verrecchia, 1994;Gradziński et al, 1997Gradziński et al, , 2012Loisy et al, 1999;Borsato et al, 2000;Benzerara et al, 2003;Richter et al, 2008;Cailleau et al, 2009a, b;Bindschedler et al, 2010). However, despite this ubiquity, the origin of calcitic nanofibres still remains unclear (Banerjee and Joshi, 2013).…”

“…Therefore, on the basis of the arguments made above, natural nanofibres might often be coated either with bounded-Ca 2+ (ionic bound), Ca 2+ -bounded macromolecules, or even CaCO 3 , all three slightly increasing their diameter. Benzerara et al (2003) observed thin amorphous layers around nanofibres and interpreted them as precursor phases of calcite crystallization. Moreover, in a further study Benzerara et al (2005) identified that carboxylic groups may be associated with their nanofibres.…”

“…Several authors have either inaccurately assimilated them into bacterial mats (Cañaveras et al, 1999) and/or thought they were genetically related to NFC (Dubroeucq et al, 1996;Gradziński et al, 1997). However, some authors have attempted to critically discuss their origin either briefly or as a whole study (Klappa, 1979;Phillips and Self, 1987;Loisy et al, 1999;Borsato et al, 2000;Benzerara et al, 2003;Cailleau et al, 2009a). Moreover, considering the origin of a feature with such dimensions, numerous hypotheses linked to nanobacteria-like objects can be discussed.…”

“…However, despite this ubiquity, the origin of calcitic nanofibres still remains unclear (Banerjee and Joshi, 2013). Three hypotheses for their formation have been proposed: (i) physicochemical processes (Jones and Ng, 1988;Jones and Khale, 1993;Borsato et al, 2000); (ii) biomineralization of rod-shaped nano-sized bacteria (Phillips and Self, 1987;Verrecchia and Verrecchia, 1994;Loisy et al, 1999;Gradziński et al, 2012); and (iii) nucleation mediated by an organic template (Benzerara et al, 2003;Olszta et al, 2004;Cailleau et al, 2009a).…”

“…These latter may act as enhancers of calcite nucleation and/or as crystal growth and shape modifiers (Benzerara et al, 2003;Benzerara et al, 2005;Olszta et al, 2004;Cailleau et al, 2009a;Zhu et al, 2009). This hypothesis lies between physicochemical and biogenic processes, as it involves the presence of organic matter, but the processes of precipitation and crystal growth do not necessarily happen as the direct result of a biological activity.…”