Fig. 2

Presence and phylogeny of nickel import genes in cable bacteria. A Presence/absence table of nickel import genes in cable bacteria and related organisms of the Desulfobulbales order. For cable bacteria, only species representatives with HQ (no circle) or complete genomes (circle) are shown. For the Desulfobulbales species, presence is only indicated if the gene is found in two or more genomes. The presence of a full operon (filled) or partial operon (half‑filled) is indicated. B Maximum-likelihood phylogeny of cable bacteria Nik/Opp/DppA protein sequences and RefSeq similarity search hits. Phylogeny inferred using IQtree according to the best-fit model (model LG + R9). Black circles indicate ultrafast bootstrap values. Cable bacteria (green branches) form a monophyletic clade (UFBoot value = 70) between sequences from the phyla Cyanobacteria and Actinomycetota. The biochemically characterized Opp1A protein sequence of S. aureus is indicated with a red arrow. Only the lowest common shared taxonomy is indicated per clade. C Maximum likelihood phylogeny of concatenated NikMQO sequences of cable bacteria and refseq database hits. Phylogeny inferred using IQtree according to the best fit model (model LG4 + F + G4). Different nikKLMNQO operon structures (based on closed genomes) and their corresponding branches are indicated within the Desulfobulbales order. The NikMQO protein sequences of Rhodobacter capsulatus are indicated with the red arrow, and the CbiMQO sequences of Rhodobacter capsulatus are indicated with the blue arrow (root). Within the Desulfogranum cluster, the putative nikO homolog is doubled in length. Note that NikMQO sequences of Ca. E. gigas neither cluster with the other cable bacteria, nor share the same operon structure. The gene neighbourhood around the nikKL locus in Ca. E. gigas and the nikMLKQ locus in all other closed cable bacteria genomes is similar. nifJ = Pyruvate‑flavodoxin oxidoreductase, pgp = Phosphoglycolate phosphatase, fd = ferredoxin, hyp. = hypothetical protein