Fig. 2

Morphological and 16S rRNA gene-based phylogenetic identification of two kinds of MTB. a Light microscopy image of MTB cells at the edge of a water droplet. The blue arrowhead indicates the slow-moving large rod-shaped MTB (LHC-1), and the orange arrowhead indicates the spherical-shaped fast-moving small magnetotactic cocci (LHC-2). b and c TEM images of a LHC-1 cell (b) and a LHC-2 cell (c). Insets of b and c: magnification of the magnetosomes in black dashed rectangles. d Crystal length distribution of LHC-1 and LHC-2 cells. e Shape factor (width/length ratio) of crystals in LHC-1 and LHC-2 cells. Each blue (LHC-1) and orange (LHC-2) dot represents one magnetosome. n = 320 (LHC-1) and 69 (LHC-2) in d and e, respectively. f Phylogenetic positions of OTU1 (LHC-1) and OTU2 (LHC-2) based on 16S rRNA gene sequences. Thirty-three previously published MTB 16S rRNA genes were used to construct the phylogenetic tree. The maximum likelihood phylogenetic tree was constructed using the MEGA v11.0.13 under the maximum composite likelihood model with the bootstrap value set to 1000. The bootstrap values of each node are indicated. Phyla names are illustrated on the right side of the figure. Besides, class names of phylum Pseudomonadota (previously known as Proteobacteria) were also illustrated, including η-proteobacteria (Magnetococcia according to the GTDB taxonomy), α-proteobacteria, and γ-proteobacteria. Branches belonging to different taxa are colored according to the names of different taxa