The Genomic Characterization of a Novel Candidatus Genus of the Family Gallionellaceae, a Novel Candidatus Species of the Genus Gallionella and Their Metabolic Potential for Iron Oxidation

The family Gallionellaceae includes neutrophilic, aerobic, iron-oxidizing bacteria, many of which remain uncultured and known only from metagenomic data. In this study, two high-quality Gallionellaceae genomes were assembled from a ferruginous spring in the Voronezh region, Russia. Phylogenetic analysis based on 120 concatenated proteins, ANI (average nucleotide identity), and AAI (average amino acid identity) indicates that BG-057 belongs to the genus Gallionella and BG-364 to the genus 39-52-133. We propose the names “Candidatus Gallionella aquifuscii” sp. nov. for BG-057 and “Candidatus Dubininella ochracea” gen. nov., sp. nov. for BG-364. Both genomes encode genes for the Calvin-Benson-Bassham (CBB) cycle. Both are potentially capable of aerobic respiration due to the presence of electron transfer chain components. Both genomes encode the iron oxidase Cyc2, and BG-057 also encodes MtoA. BG-057 is potentially capable of lithotrophic growth in the presence of H2 and H2S. BG-364 is potentially capable of growth via Mn (II) oxidation; arsenite oxidation; the direct oxidation of thiosulfate; H2S, elemental sulfur, and sulfite oxidation. BG-364 encodes denitrification genes (narGHI, nirS, norBC). BG-057 possesses systems for the biosynthesis and export of siderophores, while BG-364 lacks these systems but retains Ton-dependent receptors, suggesting the use of exogenous siderophores.