Neocallimastigomycota is a
phylum containing
anaerobicfungi, which are symbionts found in the digestive tracts of larger
herbivores. Anaerobic fungi were originally placed within phylum
Chytridiomycota, within
Order Neocallimastigales but later raised to phylum level,[3] a decision upheld by later phylogenetic reconstructions.[4] It encompasses only one
family.[3]
Discovery
The fungi in Neocallimastigomycota were first recognised as fungi by Orpin in 1975,[5] based on motile cells present in the
rumen of
sheep. Their zoospores had been observed much earlier but were believed to be
flagellateprotists, but Orpin demonstrated that they possessed a chitin cell wall.[6] It has since been shown that they are fungi related to the core chytrids. Prior to this, the
microbial population of the rumen was believed to consist only of
bacteria and
protozoa. Since their discovery they have been isolated from the
digestive tracts of over 50
herbivores, including
ruminant and non-ruminant (hindgut-fermenting) mammals and herbivorous
reptiles.[7][8]
Neocallimastigomycota have also been found in humans.[9]
Circumscription
This section is empty. You can help by
adding to it. (August 2021)
Reproduction and growth
These fungi reproduce in the rumen of ruminants through the formation of
zoospores which are released from sporangia. These zoospores bear a kinetosome but lack the nonflagellated
centriole known in most chytrids,[2] and have been known to utilize
horizontal gene transfer in their development of
xylanase (from bacteria) and other
glucanases.[10]
The
nuclear envelopes of their
cells are notable for remaining intact throughout
mitosis.[2] Sexual reproduction has not been observed in anaerobic fungi. However, they are known to be able to survive for many months in aerobic environments,[11] a factor which is important in the colonisation of new hosts. In Anaeromyces, the presence of putative resting spores has been observed [12] but the way in which these are formed and germinate remains unknown.
Neocallimastigomycota play an essential role in fibre-digestion in their host species. They are present in large numbers in the digestive tracts of animals which are fed on high fibre diets.[13] The polysaccharide degrading enzymes produced by anaerobic fungi can hydrolyse the most recalcitrant plant polymers and can degrade unlignified plant cell walls entirely.[14][15]Orpinomyces sp. exhibited the capacity of xylanase, CMCase, lichenase, amylase, β-xylosidase, β-glucosidase, α-Larabinofuranosidase and minor amounts of β-cellobiosidase production by utilizing avicel as the sole energy source.[16] The polysaccharide degrading enzymes are organised into a multiprotein complex, similar to the bacterial
cellulosome.[17]
Spelling of name
The Greek termination, "-mastix", referring to "whips", i.e. the many
flagella on these fungi, is changed to "-mastig-" when combined with additional terminations in Latinized names.[18] The family name Neocallimastigaceae was originally incorrectly published as "Neocallimasticaceae" by the publishing authors which led to the coinage of the misspelled, hence incorrect "Neocallimasticales", an easily forgiven error considering that other "-ix" endings such as Salix goes to
Salicaceae. Correction of these names is mandated by the
International Code of Botanical Nomenclature, Art. 60. The corrected spelling is used by Index Fungorum.[19] Both spellings occur in the literature and on the WWW as a result of the spelling in the original publication.
References
^Li, J.L.; et al. (1993). "The phylogenetic relationships of the anaerobic chytridiomycetous gut fungi (Neocallimasticaceae) and the Chytridiomycota. II. Cladistic analysis of structural data and description of Neocallimasticales ord. nov". Can. J. Bot. 71 (3): 393–407.
doi:
10.1139/b93-044.
S2CID83723423.
^
abHibbett, David S.; Binder, Manfred; Bischoff, Joseph F.; Blackwell, Meredith; Cannon, Paul F.; Eriksson, Ove E.; Huhndorf, Sabine; James, Timothy; Kirk, Paul M. (May 2007). "A higher-level phylogenetic classification of the Fungi". Mycological Research. 111 (5): 509–547.
CiteSeerX10.1.1.626.9582.
doi:
10.1016/j.mycres.2007.03.004.
ISSN0953-7562.
PMID17572334.
S2CID4686378.
^Mackie RI, Rycyk M, Ruemmler RL, Aminov RI, Wikelski M (2004). "Biochemical and microbiological evidence for fermentative digestion in free-living land iguanas (Conolophus pallidus) and marine iguanas (Amblyrhynchus cristatus) on the Galápagos archipelago". Physiol. Biochem. Zool. 77 (1): 127–38.
doi:
10.1086/383498.
PMID15057723.
S2CID25961316.
^Ho YW, Bar DJ (1995). "Classification of anaerobic gut fungi from herbivores with emphasis on rumen fungi from Malaysia". Mycologia. 87 (5): 655–77.
doi:
10.2307/3760810.
JSTOR3760810.
^Wilson CA, Wood TM (1992). "Studies on the cellulase of the rumen anaerobic fungus Neocallimastix frontalis, with special reference to the capacity of the enzyme to degrade crystalline cellulose". Enzyme and Microbial Technology. 14 (4): 258–64.
doi:
10.1016/0141-0229(92)90148-H.