Scientists in Germany have identified cytoskeletal structures and a gene that anchor magnetic crystals inside magnetobacteria, organisms that navigate Earth's magnetic field. The findings, which appeared online Sunday in
Magnetobacteria employ organelles known as magnetosomes, magnetite crystals enclosed in the membrane and arranged in chains that behave like compass needles. Higher organisms such as salmon and homing pigeons also possess magnetosome chains resembling those in bacteria. Recently, Schüler and his colleagues identified a cluster of at least 25 -- and possibly up to 100 -- genes in magnetobacterium
During the current study, the researchers deleted
Fluorescence microscopy and tagging MamJ with enhanced green fluorescent protein (EGFP) confirmed MamJ was linked to magnetosome vesicles, and revealed MamJ also links to a cytoskeletal structure that runs like a clothesline throughout the entire cell. Cryoelectron tomography showed this structure is made of a network of roughly four nanometer-thick filaments and is found in both wild-type and mutant
"We knew magnetosomes had to be aligning along some physical structure, but this is the first time we've seen the expression of a specific protein tied with magnetosome alignment," Radu Popa at the University of Southern California in Los Angeles, who did not participate in this study, told
"Nobody dreamed the Mam cluster was also involved with the arrangement of magnetosomes," Popa said. The fact that genes for both magnetosome formation and arrangement seem clustered together "suggests in the future we can cut out this package and express it in other bacteria that are easier to work with and potentially have the entire system, which is great news," Popa said.
"Biomineralization in general across all domains of life is not very well understood," Katrina Edwards at Woods Hole Oceanographic Institution, who did not participate in this study, told
Future experiments could knock out other magnetosome genes to learn their function, Richard Frankel at California Polytechnic State University in San Luis Obispo, also not a co-author, told
Edwards added that magnetobacteria are a very diverse group, and "we'd like to see how ubiquitous this mechanism the researchers describe is among magnetobacteria, or whether different bacteria evolve their own pathways."