Crystal habits and magnetic microstructures of magnetosomes in coccoid magnetotactic bacteria

Abstract

We report on the application of off-axis electron holography and high-resolution TEM to study the crystal habits of magnetosomes and magnetic microstructure in two coccoid morphotypes of magnetotactic bacteria collected from a brackish lagoon at Itaipu, Brazil. Itaipu-1, the larger coccoid organism, contains two separated chains of unusually large magnetosomes; the magnetosome crystals have roughly square projections, lengths up to 250 nm and are slightly elongated along [111] (width/length ratio of about 0.9). Itaipu-3 magnetosome crystals have lengths up to 120 nm, greater elongation along [111] (width/length ∼ 0.6), and prominent corner facets. The results show that Itaipu-1 and Itaipu-3 magnetosome crystal habits are related, differing only in the relative sizes of their crystal facets. In both cases, the crystals are aligned with their [111] elongation axes parallel to the chain direction. In Itaipu-1, but not Itaipu-3, crystallographic positioning perpendicular to [111] of successive crystals in the magnetosome chain appears to be under biological control. Whereas the large magnetosomes in Itaipu-1 are metastable, single-magnetic domains, magnetosomes in Itaipu-3 are permanent, single-magnetic domains, as in most magnetotactic bacteria.

Diverse phylogeny and morphology of magnetite biomineralized by magnetotactic cocci

“…Fossil remains of these biominerals (magnetofossils) have been reported widely from Cenozoic sedimentary environments and have been used to retrieve paleomagnetic and tentative paleoenvironmental information (Kirschvink and Chang, 1984; Chang and Kirschvink, 1989; Kopp and Kirschvink, 2008; Roberts et al ., 2011; Larrasoaña et al ., 2014; Savian et al ., 2014; Savian et al ., 2016; Sakuramoto et al ., 2017; Chang et al ., 2018). Studying the biodiversity and biomineralization of MTB is crucial to understand the evolution of iron mineral‐based magnetoreception within higher organisms (Lins et al ., 2006; Lin et al ., 2018; Lin et al ., 2019; Monteil et al ., 2019; Leão et al ., 2020). Such studies also provide the principal information needed to develop magnetofossils as novel biogeochemical proxies for simultaneous paleomagnetic, paleoenvironmental and paleobiological reconstructions (Kopp and Kirschvink, 2008; Jovane et al ., 2012; Li et al ., 2013a; Rodelli et al ., 2018; Yamazaki et al ., 2019; Li et al ., 2020).…”

Grazing protozoa and magnetosome dissolution in magnetotactic bacteria

“…The orientation is possible because magnetosomes impart to the bacterium a magnetic dipole moment that allows the cell to overcome the viscous drag of the water environment (Frankel, 1984). However, some magnetotactic bacteria produce more magnetic material than necessary for an efficient orientation along the geomagnetic field (Lins et al ., 2005; 2006). In addition, south‐seeking magnetotactic bacteria were reported in the Northern Hemisphere conflicting with current models of magnetotaxis (Simmons et al ., 2006).…”

Magnetotactic Bacteria and Magnetosomes: Basic Properties and Applications

“…According to high-resolution transmission electron microscopy [87], faceting of magnetosome crystals by planes with high Miller indices [136] is apparently determined by a multistage biomineralization process, controlled by anions and organic molecules inside a vesicle and other intra- [80] and extracellular [137] factors, and may differ for magnetosomes within the same chain [81]. Formation of ε-Fe 2 O 3 at an intermediate stage of biomineralization in magnetosomes has been hypothesized [138].…”