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

## TL;DR

Scientists discovered a new type of ocean bacteria that makes magnetic crystals in chains and has unique features, expanding our knowledge of magnetic bacteria.

## Contribution

The study presents the first genomic and phylogenetic analysis of a novel magnetotactic coccus with multi-chain magnetosomes.

## Key findings

- Strain HHB-1 is a large marine magnetotactic coccus with multiple chains of prismatic magnetite magnetosomes.
- Genomic analysis shows HHB-1 represents a new lineage within the Magnetococcales with a nearly complete magnetosome gene cluster.
- HHB-1 contains Ca/Mg-rich polyphosphate granules and has low amino acid identity with known MTB strains.

## Abstract

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.

A novel marine magnetotactic coccus, strain HHB‐1, was isolated from intertidal sediments in Houhai Bay, China. HHB‐1 cells are large coccoid–ovoid bacteria that contain multiple chains of prismatic magnetite magnetosomes and conspicuous Ca/Mg‐rich polyphosphate granules. Genomic and phylogenomic analyses reveal that HHB‐1 represents a new deeply branching lineage within the Magnetococcales and harbours a nearly complete and conserved magnetosome gene cluster, providing the first genomic insights into a magnetococcus with multi‐chain magnetosomes.