Chemical signature of magnetotactic bacteria

Abstract

There are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite. On Earth, magnetotactic bacteria perform biomineralization of intracellular magnetite nanoparticles under a controlled pathway. These bacteria are ubiquitous in modern natural environments. However, their identification in ancient geological material remains challenging. Together with physical and mineralogical properties, the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification, but this had never been explored quantitatively and systematically for many trace elements. Here, we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1. We show that, in biomagnetite, most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion. Furthermore, we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record.

Magnetite as a precursor for green rust through the hydrogenotrophic activity of the iron‐reducing bacteria Shewanella putrefaciens

“…The iron isotopic ratio, an indication of bacterial involvement (Johnson et al, 2008), measured in 2.9-billion-year-old magnetite grains is very close to that observed in current magnetite samples resulting from the dissimilatory reduction of Fe III species (Yamaguchi et al, 2005). Other isotopic ratios can also serve to the determination of the formation of magnetite by bacterial activity (magnetotactic bacteria) such as the strontium/calcium ratio (Amor et al, 2015). However, it is still uncertain that GR played a role during primitive bacterial iron-reducing and iron-oxidizing activities, although the presence of GR and magnetite has been observed in an analog of Precambrian ocean (Zegeye et al, 2012).…”

“…These geological structures, composed of ferric oxide-rich layers (such as magnetite and hematite) alternating with ferrous carbonate-rich layers (such as siderite), are thought to have been formed by primitive bacterial activity with dihydrogen as the most probable electron donor (Konhauser, 2007). Other isotopic ratios can also serve to the determination of the formation of magnetite by bacterial activity (magnetotactic bacteria) such as the strontium/calcium ratio (Amor et al, 2015). Other isotopic ratios can also serve to the determination of the formation of magnetite by bacterial activity (magnetotactic bacteria) such as the strontium/calcium ratio (Amor et al, 2015).…”

The cation diffusion facilitator protein MamM’s cytoplasmic domain exhibits metal-type dependent binding modes and discriminates against Mn2+

“…Thus, PELDOR taken together with the tryptophan fluorescence and ITC data provide clear evidence of the inability of MamM CTD to bind Mn 2+ . Mn 2+ has a greater affinity to magnetite, both when abiotically synthesised or in magnetotactic bacteria as compared to other transition metal cations (Amor et al, 2015). Furthermore, uncultivated magnetotactic bacteria, which are exposed to high concentrations of manganese, can incorporate it into the iron-based magnetic particles (Keim et al, 2009).…”

Phylogenetic and Structural Identification of a Novel MagnetotacticDeltaproteobacteriaStrain, WYHR-1, from a Freshwater Lake

“…After MTB die and lyse, magnetosomes can be preserved as magnetofossils within sediments or sedimentary rocks (10,11). Compared to detrital and other magnetite crystals not produced by MTB, magnetofossils have distinctive physical, chemical, crystallographic, and magnetic features (12)(13)(14)(15)(16), which makes them ideal recorders of paleomagnetic and paleoenvironmental information (17)(18)(19)(20)(21). They could also be used to calibrate potential biomarker searches in ancient terrestrial and/or even extraterrestrial environments (10,22,23).…”