Type strain is Allofontibacter medardicus ME-17 (GCA_965235075.1), isolated from 5 m depth from Lake Medard, Czechia (date: 2019-10-22), via high-throughput dilution to extinction cultivation. ME-17 has a genome size of 1.1 Mbp with a genomic GC content of 29.6%, contains 3 rRNA genes and 31 tRNAs. The genome is complete, consisting of a circular chromosome. The genome contains genes encoding rhodopsins and the biosynthetic pathway for retinal biosynthesis. No genes for flagella or pilus assembly and chemotaxis were annotated. Pathways for glycolate oxidation and the biosynthesis of 16 amino acids were predicted. Further, pathways for riboflavin, NAD, coenzyme A, and heme biosynthesis were identified. The closest cultivated relatives are ‘Candidatus Fonsibacter ubiquis’ LSUCC0530 (GCF_002688585.1; later reclassified to ‘Ca. Allofontibacter communis’), with an average amino acid identity of 87.2% and average nucleotide identity of 85.2% and another newly proposed species, Allofontibacter abundans MiE-29 (GCA_965235095.1), with an AAI of 92.7% and an ANI of 91.1%. Current GTDB classification (R220): d__Bacteria; p__Pseudomonadota; c__Alphaproteobacteria; o__Pelagibacterales; f__Pelagibacteraceae; g__Fonsibacter; s__Fonsibacter sp018882565.