North-Seeking Magnetotactic Gammaproteobacteria in the Southern Hemisphere

Abstract

Magnetotactic bacteria (MTB) comprise a phylogenetically diverse group of prokaryotes capable of orienting and navigating along magnetic field lines. Under oxic conditions, MTB in natural environments in the Northern Hemisphere generally display north-seeking (NS) polarity, swimming parallel to the Earth's magnetic field lines, while those in the Southern Hemisphere generally swim antiparallel to magnetic field lines (south-seeking [SS] polarity). Here, we report a population of an uncultured, monotrichously flagellated, and vibrioid MTB collected from a brackish lagoon in Brazil in the Southern Hemisphere that consistently exhibits NS polarity. Cells of this organism were mainly located below the oxic-anoxic interface (OAI), suggesting it is capable of some type of anaerobic metabolism. Magnetosome crystalline habit and composition were consistent with elongated prismatic magnetite (Fe 3 O 4 ) particles. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that this organism belongs to a distinct clade of the Gammaproteobacteria class. The presence of NS MTB in the Southern Hemisphere and the previously reported finding of SS MTB in the Northern Hemisphere reinforce the idea that magnetotaxis is more complex than we currently understand and may be modulated by factors other than O 2 concentration and redox gradients in sediments and water columns. IMPORTANCEMagnetotaxis is a navigational mechanism used by magnetotactic bacteria to move along geomagnetic field lines and find an optimal position in chemically stratified sediments. For that, magnetotactic bacteria swim parallel to the geomagnetic field lines under oxic conditions in the Northern Hemisphere, whereas those in the Southern Hemisphere swim antiparallel to magnetic field lines. A population of uncultured vibrioid magnetotactic bacteria was discovered in a brackish lagoon in the Southern Hemisphere that consistently swim northward, i.e., the opposite of the overwhelming majority of other Southern Hemisphere magnetotactic bacteria. This finding supports the idea that magnetotaxis is more complex than previously thought.

Magnetosome magnetite biomineralization in a flagellated protist: evidence for an early evolutionary origin for magnetoreception in eukaryotes

“…The elongation axis of magnetosomes in these species varies in the <100>, <110> and <111> crystallographic directions. Those present in the flagellate described here are elongated along [100], the elongation axis described for deep‐branching, presumably older, evolutionary groups of MTB (Li et al ., ; Leão et al ., ). In addition, in these deep‐branching MTB, the anisotropic magnetosomes are organized as bundles of multiple chains (Li et al ., ; Lefèvre et al ., ).…”

“…Samples of water and sediment were collected in Ubatiba (Maricá, RJ, Brazil; 22°52′49.0″S, 42°48′04.6″W) and Ururaí (Campos dos Goytacazes, RJ, Brazil; 21°45′30.5″S, 41°28′38.4″W) rivers as previously described (Leão et al ., ) during 2015 and 2016. Samples were stored for up to 2 months at room temperature with indirect sunlight.…”

Ectosymbiotic bacteria at the origin of magnetoreception in a marine protist

“…This atypical anterior–posterior orientation of the cells polarity regarding the magnetic moment seems to be restricted only to anaerobes, which seek the surface at the bottom limit of the oxic–anoxic transition zone, instead of the deep. The benefit for the magnetic protist remains to be fully determined but might be similar to that attributed to free-living magnetotactic bacteria with the same unusual magnetotactic behaviour 25,26 : magnetotaxis could facilitate protist navigation towards chemical and redox optimal niches through sensors that have a different response to chemical gradients. On the bacterial side, several advantages may be hypothesized.…”

Diversity and ecology of and biomineralization by magnetotactic bacteria

“…Since then, a growing number of MTB populations have been discovered, demonstrating their high morphological and phylogenetic diversity (e.g. Flies et al ., ; Pan et al ., ; Abreu et al ., ; Simmons and Edwards, ; Lin et al ., ; Lin and Pan, ; Lefèvre et al ., ; Kolinko et al ., ; Zhang et al ., ; Zhou et al ., ; Chen et al ., ; Fuduche et al ., ; Pradel et al ., ; Leão et al ., ). In particular, Kolinko et al .…”