Bor.rel.i.el'la. N.L. fem. dim. n. Borreliella named after Amédée Borrel (1867–1936). Spirochaetes / Spirochaetes / Spirochaetales / Borreliaceae / Borreliella Cells are helical, 0.2–0.3 µm in diameter, 15–30 µm in length, and do not have hooked ends. Coils are regular or irregular in spacing and amplitude. Motile. Inner and outer membranes with overlapping periplasmic flagella; 7–11 subterminal insertion points in most species. Aniline‐stain‐positive. Microaerophilic. Ferments glucose. Most species are cultivable in complex, serum‐containing media that include N‐acetylglucosamine. Optimum growth is between 33 and 38°C. Cells are polyploid, with each genome comprising a linear chromosome and one or more linear and circular plasmids. All known species are host‐associated organisms that are transmitted among mammalian, avian, and reptile reservoirs by a tick of the prostriate genus Ixodes. In unfed ticks, the organisms are located in the midgut and only travel to the salivary glands once the next blood meal commences. Transovarial transmission in tick vector does not occur. Members of this genus include all known agents of Lyme disease (Lyme borreliosis) as well as several species not associated with human disease. DNA G + C content (mol%): 28–29. Type species: Borreliella burgdorferi (Adeolu and Gupta 2014, VL163) (basonym: Borrelia burgdorferi Johnson et al. 1984bVP).

Thiamin pyrophosphate (ThDP), the active form of thiamin (vitamin B₁), is believed to be an essential cofactor for all living organisms^1,2. Here, we report the unprecedented result that thiamin is dispensable for the growth of the Lyme disease pathogen Borrelia burgdorferi (Bb)³. Bb lacks genes for thiamin biosynthesis and transport as well as known ThDP-dependent enzymes⁴, and we were unable to detect thiamin or its derivatives in Bb cells. We showed that eliminating thiamin in vitro and in vivo using BcmE, an enzyme that degrades thiamin, has no impact on Bb growth and survival during its enzootic infectious cycle. Finally, high-performance liquid chromatography analysis reveals that the level of thiamin and its derivatives in Ixodes scapularis ticks, the enzootic vector of Bb, is extremely low. These results suggest that by dispensing with use of thiamin, Borrelia, and perhaps other tick-transmitted bacterial pathogens, are uniquely adapted to survive in tick vectors before transmitting to mammalian hosts. To our knowledge, such a mechanism has not been reported previously in any living organisms.