Neocallimastigomycota

Lore & Background

The fungi in Neocallimastigomycota were first recognized as fungi by Orpin in 1975, based on motile cells found in the rumen of sheep. Their zoospores had been observed earlier but were mistaken for flagellate protists; Orpin demonstrated they possess a chitin cell wall. Since then, they have been isolated from over 50 herbivores, including ruminant and non-ruminant mammals and herbivorous reptiles. Prior to their discovery, the rumen microbial population was believed to consist only of bacteria and protozoa.

Reader's Guide

Neocallimastigomycota are significant because they fill a unique ecological niche as anaerobic fungi that break down plant fiber in the digestive systems of large herbivores. Their polysaccharide-degrading enzymes can hydrolyze the most recalcitrant plant polymers and degrade unlignified plant cell walls entirely. They lack mitochondria but contain hydrogenosomes, where oxidation of NADH leads to H2 formation. Their nuclear envelopes remain intact throughout mitosis, and sexual reproduction has not been observed. They can survive for months in aerobic environments, aiding colonization of new hosts. The phylum's name derives from Greek '-mastix' (whips), referring to their many flagella; a spelling correction was mandated by the International Code of Botanical Nomenclature.

Did You Know?

• Neocallimastigomycota were originally placed in the phylum Chytridiomycota before being raised to phylum level.
• Their zoospores bear a kinetosome but lack the nonflagellated centriole found in most chytrids.
• They have been found in over 50 herbivore species.
• The correct family name is Neocallimastigaceae, and the order is Neocallimastigales.