Characterization and Phylogenetic Analysis of a Novel Uncultivated Magnetotactic Coccus Harbouring Multi‐Chain Magnetosomes

Magnetotactic bacteria (MTB) are a diverse group of microorganisms that synthesize intracellular magnetic nanocrystals termed magnetosomes. In this study, a novel marine magnetotactic coccus, designated strain HHB‐1, was magnetically enriched from intertidal sediments in Houhai Bay, southern China. Optical microscopy, electron microscopy and elemental analysis revealed that HHB‐1 cells are relatively large coccoid‐ovoid bacteria (3.9 ± 0.3 μm × 2.8 ± 0.2 μm) containing multiple chains of prismatic magnetite magnetosomes and prominent intracellular Ca/Mg‐rich polyphosphate (Ca‐Mg‐polyP) granules. Whole‐genome sequencing and phylogenomic analyses revealed that HHB‐1 represents a novel and deeply branching lineage within the order Magnetococcales , exhibiting low average amino acid identity (57.3%–58.7%) with previously reported strains. The magnetosome gene cluster (MGC) of HHB‐1 comprises a nearly complete set of mam (magnetosome membrane) genes with conserved gene order and structure, representing the first genomic and MGC characterization of a novel magnetococcus possessing multi‐chain magnetosomes. These findings expand our understanding of the diversity, biomineralization strategies and evolutionary history of MTB in marine environments.