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.