Type genome is Fontibacterium oligotrophicum N-Balt2-05jul22-047 (GCA_965235975.1), a metagenome-assembled genome (MAG) assembled from 0.5 m depth from the slightly brackish part of Vistula Lagoon, Poland (date: 2022-07-05). N-Balt2-05jul22-047 has a genome size of 0.92 Mbp with a genomic GC content of 29.4% and contains 30 tRNAs. The genome is of high quality, consisting of 3 contigs, with a completeness of 96.4%, contamination of 0% and strain heterogeneity of 0% as assessed with checkM. The metagenome was assembled with FLYE from combined long- and short-read sequencing (Oxford Nanopore and Illumina NovaSeq). Metagenomic fragment recruitment of >600 samples from five continents indicate that the species is highly abundant in oligotrophic lakes in temperate and subtropical regions. The closest cultivated relatives are Fontibacterium commune, syn. ‘Candidatus Fonsibacter ubiquis’ LSUCC0530 (GCF_002688585.1; later reclassified to ‘Ca. Allofontibacter communis’), with an average amino acid identity of 92.57% and average nucleotide identity of 90.07% and another newly proposed species, Fontibacterium medardicus ME-17 (GCA_965235075.1), with an AAI of 85.45% and an ANI of 88.16%. Current GTDB classification (R220): d__Bacteria; p__Pseudomonadota; c__Alphaproteobacteria; o__Pelagibacterales; f__Pelagibacteraceae; g__Fonsibacter; s__Fonsibacter sp947497305.