UC Irvine

Abstract Bor.rel.i.a.ce'ae. N.L. fem. n. Borrelia type genus of the family; suff. ‐ aceae ending to denote a family; N.L. fem. pl. n. Borreliaceae , the family of Borrelia . Cells are helical with regular or irregular coils, 0.2–0.3 µm in diameter and 10–40 µm in length. Cells do not have hooked ends. Motile. Inner and outer membrane with periplasmic flagella with 7–20 subterminal insertion points. Aniline‐stain‐positive. Microaerophilic. Most members of the family cultivable in complex media that includes N ‐acetylglucosamine. Optimum growth between 33°C and 38°C. Diamino acid of peptidoglycan is ornithine. Lacks a lipopolysaccharide. Linear chromosome and plasmids with hairpin telomeres. The family currently accommodates the genera Borrelia and Borreliella . Members of the family are host‐associated organisms that are transmitted between vertebrate reservoirs by a hematophagous arthropod, in all but one case, a tick. Members include the agents of relapsing fever, Lyme disease, and avian spirochetosis. DNA G + C content (mol%) : 26–30. Type genus : Borrelia Swellengrebel 1907, 562 AL . Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the family Borreliaceae is: correct name (last update, April 2026) * . LPSN classification: Bacteria / Pseudomonadati / Spirochaetota / Spirochaetia / Spirochaetales / Borreliaceae The family Borreliaceae can also be recovered in the Genome Taxonomy Database (GTDB) as f__Borreliaceae (version v232) ** . GTDB classification: d__Bacteria / p__Spirochaetota / c__Spirochaetia / o__Borreliales / f__Borreliaceae * Freese , H.M. , Meier‐Kolthoff , J.P. , Sardà Carbasse , J. , Afolayan , A.O. , Göker , M. ( 2026 ). TYGS and LPSN in 2025: a Global Core Biodata Resource for genome‐based classification and nomenclature of prokaryotes within DSMZ Digital Diversity. Nucleic Acids Res , 54 (), D884 – D891 ; doi: 10.1093/nar/gkaf1110 ** Parks , D.H. , Chaumeil , P.‐A. , Mussig , A.J. , Rinke , C. , Chuvochina , M. , Hugenholtz , P. ( 2026 ). GTDB release 10: a complete and systematic taxonomy for 715.230 bacterial and 17.245 archaeal genomes. Nucleic Acids Res , 54 (), D743 – D754 ; doi: 10.1093/nar/gkaf1040