segmented filamentous bacteria

{{Short description|Type of bacteria}}

{{Automatic taxobox

| image =

| image_alt =

| image_caption =

| taxon = Candidatus Savagella

| authority = Thompson et al. 2012 non Foerste 1920 non Geis 1932

| type_species = "Ca. Savagella gallinara"

| type_species_authority = Gilroy et al. 2021

| subdivision_ranks = Species

| subdivision =

• "Ca. S. gallinara"

| synonyms_ref =

| synonyms =

• "Ca. Dwaynia" Thompson et al. 2012 corrig. Oren et al. 2017
• Dwaynesavagella Thompson et al. 2012 corrig. Oren et al. 2020

}}

Segmented filamentous bacteria or Candidatus Savagella are members of the gut microbiota of rodents, fish and chickens, and have been shown to potently induce immune responses in mice.{{Cite journal | last1 = Ivanov | first1 = I. I. | last2 = Littman | first2 = D. R. | doi = 10.1038/mi.2010.3 | title = Segmented filamentous bacteria take the stage | journal = Mucosal Immunology | volume = 3 | issue = 3 | pages = 209–212 | year = 2010 | pmid = 20147894| pmc =3010405 }} They form a distinct lineage within the Clostridiaceae and the name Candidatus Savagella has been proposed for this lineage.{{Cite journal | last1 = Thompson | first1 = C. L. | last2 = Vier | first2 = R. | last3 = Mikaelyan | first3 = A. | last4 = Wienemann | first4 = T. | last5 = Brune | first5 = A. | title = 'Candidatus Arthromitus' revised: Segmented filamentous bacteria in arthropod guts are members of Lachnospiraceae| doi = 10.1111/j.1462-2920.2012.02731.x | journal = Environmental Microbiology | pages = 1454–65 | year = 2012 | pmid = 22436008 | volume=14 | issue=6| bibcode = 2012EnvMi..14.1454T }}

They were previously named Candidatus Arthromitus because of their morphological resemblance to bacterial filaments previously observed in the guts of insects by Joseph Leidy.Leidy, J. 1849. On the existence of entophyta in healthy animals, as a natural condition. Proc. National Academy of Sciences. USA 4:225–233

Despite the fact that they have been widely referred to as segmented filamentous bacteria, this term is somewhat problematic as it does not allow one to distinguish between bacteria that colonize various hosts or even if segmented filamentous bacteria are actually several different bacterial species. In mice, these bacteria grow primarily in the terminal ileum in close proximity to the intestinal epithelium where they are thought to help induce T helper 17 cell responses.{{Cite journal| last1 = Ivanov | first1 = I.| last2 = Atarashi | first2 = K.| last3 = Manel | first3 = N.| last4 = Brodie | first4 = E.| last5 = Shima | first5 = T.| last6 = Karaoz | first6 = U.| last7 = Wei | first7 = D.| last8 = Goldfarb | first8 = K.| last9 = Santee | first9 = C.| last10 = Lynch | first10 = S. V.| last11 = Tanoue | first11 = T.| last12 = Imaoka | first12 = A.| last13 = Itoh | first13 = K.| last14 = Takeda | first14 = K.| last15 = Umesaki | first15 = Y.| last16 = Honda | first16 = K.| last17 = Littman | first17 = D. R.| title = Induction of intestinal Th17 cells by segmented filamentous bacteria| journal = Cell| volume = 139| issue = 3| pages = 485–498| year = 2009| pmid = 19836068| pmc = 2796826| doi = 10.1016/j.cell.2009.09.033}}

Intriguingly, Segmented Filamentous Bacteria were found to expand in AID-deficient mice, which lack the ability to mount an appropriate humoral immune response because of impaired somatic hypermutation; parabiotic experiments revealed the importance of IgA in eliminating Segmented Filamentous Bacteria.{{Cite journal| last1 = Suzuki | first1 = K.| last2 = Meek | first2 = B.| last3 = Doi | first3 = Y.| last4 = Muramatsu | first4 = M.| last5 = Chiba | first5 = T.| last6 = Honjo | first6 = T.| last7 = Făgărășan | first7 = S. |author-link7 = Sidonia Făgărășan | title = Aberrant expansion of segmented filamentous bacteria in IgA-deficient gut| journal = Proceedings of the National Academy of Sciences of the United States of America| volume = 101| issue = 7| pages = 1981–1986| year = 2004| pmid = 14766966| pmc = 357038| doi = 10.1073/pnas.0307317101|bibcode = 2004PNAS..101.1981S | doi-access = free}} This goes hand in hand with an earlier study demonstrating the ability of monocolonization with Segmented Filamentous Bacteria to dramatically increase mucosal IgA levels.{{Cite journal| last1 = Klaasen | first1 = H. L.| last2 = Van Der Heijden | first2 = P. J.| last3 = Stok | first3 = W.| last4 = Poelma | first4 = F. G.| last5 = Koopman | first5 = J. P.| last6 = Van Den Brink | first6 = M. E.| last7 = Bakker | first7 = M. H.| last8 = Eling | first8 = W. M.| last9 = Beynen | first9 = A. C.| title = Apathogenic, intestinal, segmented, filamentous bacteria stimulate the mucosal immune system of mice| journal = Infection and Immunity| volume = 61| issue = 1| pages = 303–306| year = 1993| doi = 10.1128/IAI.61.1.303-306.1993| pmid = 8418051| pmc = 302719}} Segmented Filamentous Bacteria are species specific, and may be important to immune development.