Isolation and cultivation of a novel freshwater magnetotactic coccus FCR-1 containing unchained magnetosomes

Magnetotactic bacteria are ubiquitous aquatic prokaryotes that have the ability to biomineralize magnetite (Fe₃O₄) and/or greigite (Fe₃S₄) nanoparticles called magnetosomes. Magnetotactic cocci belonging to the class "Ca. Magnetococcia" are most frequently identified in freshwater habitats, but remain uncultivated. Here, we report for the first time axenic cultivation of freshwater magnetotactic coccus FCR-1 isolated from Chichijima, Japan. Strain FCR-1 grows microaerophilically in a semi-solid gellan gum medium. We find that strain FCR-1 biomineralizes Fe₃O₄ nanoparticles, which are not chained, into a cell. Based on phylogenomic analysis, compared with strains of the class "Ca. Magnetococcia", strain FCR-1 represents a novel genus of candidate family "Ca. Magnetaquicoccaceae" within the class "Ca. Magnetococcia" and we tentatively name this novel genus "Ca. Magnetaquiglobus chichijimensis". Our isolate provides a promising tool for elucidating the functions of unchained magnetosomes, the global distribution of magnetotactic bacteria and the origin of magnetotaxis.