Type genome is Fontibacterium subtropicum N-SamH-20apr23-026 (GCA_965235415.1), a metagenome-assembled genome (MAG) assembled from 15 m depth from Lake Samsonvale, Australia (date: 2023-04-20). N-SamH-20apr23-026 has a genome size of 1.15 Mbp with a genomic GC content of 29.3%, contains 3 rRNA genes and 34 tRNAs. The genome is of high quality, consisting of 100 contigs, with a completeness of 100%, contamination of 1.2% and strain heterogeneity of 100% 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 present mainly in subtropical lakes. 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 88.13% and average nucleotide identity of 85.63% and another newly proposed species, Fontibacterium medardicus ME-17 (GCA_965235075.1), with an AAI of 90.92% and an ANI of 88.79%. Current GTDB classification (R220): d__Bacteria; p__Pseudomonadota; c__Alphaproteobacteria; o__Pelagibacterales; f__Pelagibacteraceae; g__Fonsibacter; s__Fonsibacter sp023257975.