Summary
The name
Arthromitus
has been applied collectively to conspicuous filamentous bacteria found in the hindguts of termites and other arthropods. First observed by Joseph Leidy in 1849, the identity of these filaments has remained contentious. While Margulis and colleagues declared them to be a life stage of
Bacillus cereus
, others have assumed them to belong to the same lineage as the segmented filamentous bacteria (SFB) from vertebrate guts, a group that has garnered much attention due to their unique ability to specifically modulate their host's immune response. Both SFB and
Arthromitus
filaments from arthropod guts were grouped under provisional name ‘
Candidatus
Arthromitus’ by Snel and colleagues as they share a striking similarity in terms of their morphology and close contact to the host gut wall. While SFB form a distinct lineage within the family
Clostridiaceae
, the identity of the filaments from arthropod guts remains elusive. Using whole‐genome amplification of single filaments capillary picked from termite guts and fluorescence
in situ
hybridization of 16S rRNA with group‐specific oligonucleotide probes, we show that they represent a monophyletic lineage within the family
Lachnospiraceae
distinct from that of SFB. Therefore, ‘
Candidatus
Arthromitus’ can no longer be used for both groups. Given the historic precedence, we propose to reserve this name for the filaments that were originally described by Leidy. For the SFB from vertebrate guts, we propose the provisional name ‘
Candidatus
Savagella’ in honour of the American gut microbiologist Dwayne C. Savage, who was the first to describe that important bacterial group.