Neocallimastigomycota

Neocallimastigomycota is a phylum containing anaerobic fungi, 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]

Neocallimastigomycota
Scientific classification
Kingdom: Fungi
Division: Neocallimastigomycota
M.J. Powell 2007[1]
Class: Neocallimastigomycetes
M.J. Powell 2007[1]
Order: Neocallimastigales
J.L. Li, I.B. Heath & L. Packer[2]
Family: Neocallimastigaceae
Type genus
Neocallimastix
(I.B. Heath 1983) Vavra & Joyon
Genera

Agriosomyces
Aklioshbomyces
Anaeromyces
Buwchfawromyces
Caecomyces
Capellomyces
Cyllamyces
Ghazallomyces
Joblinomyces
Khoyollomyces
Neocallimastix
Oontomyces
Orpinomyces
Pecoramyces
Piromyces
Tahromyces

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 flagellate protists, 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]

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,[1] 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.[1] 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.

Metabolism

Neocallimastigomycota lack mitochondria but instead contain hydrogenosomes in which the oxidation of NADH to NAD+, leading to formation of H2.[10]

Polysaccharide-degrading activity

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] The polysaccharide degrading enzymes are organised into a multiprotein complex, similar to the bacterial cellulosome.[16]

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.[17] 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.[18] Both spellings occur in the literature and on the WWW as a result of the spelling in the original publication.

References
  1. Hibbett, D.S.; et al. (March 2007). "A higher level phylogenetic classification of the Fungi". Mycological Research. 111 (5): 509–547. CiteSeerX 10.1.1.626.9582. doi:10.1016/j.mycres.2007.03.004. PMID 17572334.
  2. 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. S2CID 83723423.
  3. Hibbett, 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. CiteSeerX 10.1.1.626.9582. doi:10.1016/j.mycres.2007.03.004. ISSN 0953-7562. PMID 17572334.
  4. Tedersoo, Leho; Sánchez-Ramírez, Santiago; Kõljalg, Urmas; Bahram, Mohammad; Döring, Markus; Schigel, Dmitry; May, Tom; Ryberg, Martin; Abarenkov, Kessy (2018-05-16). "High-level classification of the Fungi and a tool for evolutionary ecological analyses". Fungal Diversity. 90: 135–159. doi:10.1007/s13225-018-0401-0. ISSN 1560-2745.
  5. Orpin CG (December 1975). "Studies on the rumen flagellate Neocallimastix frontalis". J. Gen. Microbiol. 91 (2): 249–62. doi:10.1099/00221287-91-2-249. PMID 1462.
  6. Orpin, C. G. (1977). "The occurrence of chitin in the cell walls of the rumen organisms Neocallimastix frontalis, Piromonas communis and Sphaeromonas communis" (PDF). Journal of General Microbiology. 99 (1): 215–218. doi:10.1099/00221287-99-1-215. PMID 864435.
  7. Ljungdahl LG (March 2008). "The cellulase/hemicellulase system of the anaerobic fungus Orpinomyces PC-2 and aspects of its applied use". Ann. N. Y. Acad. Sci. 1125 (1): 308–21. Bibcode:2008NYASA1125..308L. doi:10.1196/annals.1419.030. PMID 18378601. S2CID 20006974.
  8. 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. PMID 15057723. S2CID 25961316.
  9. Rodríguez M, Pérez D, Chaves FJ, Esteve E, Garcia PM, Xifra G, Vendrell J, Jové M, Pamplona R, Ricart W, Otin MP, Chacón MR (2015). "Obesity changes the human gut mycobiome". Scientific Reports. 5: 14600. Bibcode:2015NatSR...514600M. doi:10.1038/srep14600. PMC 4600977. PMID 26455903.
  10. C.J. Alexopolous, Charles W. Mims, M. Blackwell, Introductory Mycology, 4th ed. (John Wiley and Sons, Hoboken NJ, 2004) ISBN 0-471-52229-5
  11. McGranaghan, P.; Davies, J. C.; Griffith, G. W.; Davies, D. R.; Theodorou, M. K. (1999-07-01). "The survival of anaerobic fungi in cattle faeces". FEMS Microbiology Ecology. 29 (3): 293–300. doi:10.1111/j.1574-6941.1999.tb00620.x. ISSN 0168-6496.
  12. Brookman, Jayne L.; Ozkose, Emin; Rogers, Siân; Trinci, Anthony P. J.; Theodorou, Michael K. (2000-03-01). "Identification of spores in the polycentric anaerobic gut fungi which enhance their ability to survive". FEMS Microbiology Ecology. 31 (3): 261–267. doi:10.1111/j.1574-6941.2000.tb00692.x. ISSN 0168-6496. PMID 10719208.
  13. 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. JSTOR 3760810.
  14. Akin DE, Borneman WS (October 1990). "Role of rumen fungi in fiber degradation". J. Dairy Sci. 73 (10): 3023–32. doi:10.3168/jds.S0022-0302(90)78989-8. PMID 2178175.
  15. Selinger LB, Forsberg CW, Cheng KJ (October 1996). "The rumen: a unique source of enzymes for enhancing livestock production". Anaerobe. 2 (5): 263–84. doi:10.1006/anae.1996.0036. PMID 16887555.
  16. 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.
  17. combform3.qxd Archived 2007-03-15 at the Wayback Machine
  18. Suprafamilial Names
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