Evidence of Magnetotactic Bacteria in Meteorites

Magnetosomes and magnetite associated with magnetotactic bacteria are valid biomarkers. Anaerobic or microaerobic microorganisms produce magnetosomes with recognizable properties and definitive evidence of biogenicity. In 1975, Blakemore [99] announced the discovery of a magnetotactic bacterium, which he named Aquasprillum magnetotacticum, Schleiffer et al. [100] later transferred this species to the new genus, Magnetospirillum gen. nov., and described a new species, Magnetospirillum gryphiswaldense. Several other species of magnetotactic bacteria and algae have subsequently been found in anaerobic, microaerobic environments, and in soils, permafrost, and loess [101,102]. These microorganisms produce membrane-bounded magnetic crystals of magnetite (Fe3O4) or griegite (Fe3S4) [103-104]. The magnetite crystals are uniform and in the single-magnetic domain size range (typically about 35 to 150 nm) [105].

Matrix-controlled biomagnetite crystals are specific to species and occur in several configurations, e.g.: cubo-octahedral, elongated hexagonal prismatic, or bullet shaped. To optimize the magnetic properties, microorganisms usually configure the magnetites into one or more chains-of-pearls strands along the longitudinal axis of the organism [106,107]. Axis dipoles are oriented with the crystal axis—magnetite [108] or griegite [109] aligned to the chain direction. These microstructures are strong biomarkers because their unique morphological properties and chain-of-pearls distribution can be recognized in living organisms and rocks, and they distinguish biological magnetosomes from abiotic. Iron-reducing bacteria can also produce extracellular magnetite globules by dissimilatory iron reduction. The biomagnetite crystals produced in this way may exhibit lower crystallinity and a wider grain size than those found in magnetosomes. Mckay et al. [110] recently showed that the parallelepiped magnetites of ALH84001 exhibit the precise characteristics of biogenic magnetites. These results provide strong evidence for biogenic activity in this ancient Mars meteorite. Microfossils of magnetotactic bacteria with chains of magnetosomes and/or extracellular magnetites have now been detected in several meteorites, e.g.: ALH84001, Orgueil, Nogoya, and the Tagish Lake meteorites.

Dissimilatory

Figure 6. (a) Orgueil microfossil with extracellular magnetite and chain-of-pearls magnetosomes, (b) magne-tosomes in living purple sulfur bacteria Rhodopseudomonas rutilis, (c) ESEM image of microfossils in Nogoya carbonaceous meteorite and two-dimensional X-ray Maps in (d) Al, (e) Ca, (f) Fe, (g) O, and (h) S.

Figure 6. (a) Orgueil microfossil with extracellular magnetite and chain-of-pearls magnetosomes, (b) magne-tosomes in living purple sulfur bacteria Rhodopseudomonas rutilis, (c) ESEM image of microfossils in Nogoya carbonaceous meteorite and two-dimensional X-ray Maps in (d) Al, (e) Ca, (f) Fe, (g) O, and (h) S.

In 1967, Tan and VanLandingham [111] conducted transmission electron microscopy (TEM) studies of acid-resistant biological-like microstructures that they found in the Orgueil carbonaceous meteorite. They found numerous acid resistant cylindrical forms that were rounded on one end and tapered at the other (Fig. 6 (a)). TEM images show electron-dense magnetites aligned as a chain of pearls along the longitudinal axis. Vainshtein [112,113] provided TEM images of living purple sulfur bacteria, Rhodopseudomonas rutilis, with similar configuration of magnetosomes (Fig. 6 (b)). An iron- and oxygen-rich microfossil in the Nogoya carbonaceous meteorite, which has similar microstructure to the magnetotactic microfossils of Orgueil, is shown in Fig. 6 (c) along with an accompanying ESEM image and two-dimensional x-ray maps showing the Al, Ca, Fe, O, and S distributions.

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment