Neocallimastix Vávra & Joyon ex I.B. Heath

The genus Neocallimastix was described by Vavra and Joyon (1966). At that time, the propensity for nutritional microbiologists to work with rumen fluid and discard rumen solids meant that the solids-associated vegetative stage of the fungus was not recognized. The zoospores of the fungus evident in rumen fluid were therefore mistakenly identified as polyflagellated protozoans. The correct identification of these zoospores by Orpin’s pioneering studies showed that the ‘flagellates’ were liberated from a benthic, vegetative stage of a ‘chytrid-like’ fungus (Orpin 1975). Soon after his initial observations, chitin was identified in the fungal cell walls and by 1989 a new classification had emerged to accommodate these obligately anaerobic (oxygen intolerant) fungi (Orpin 1977a, b; Barr et al. 1989). Anaerobic fungi from this genera are among the most studied of all the anaerobic fungi. Numerous isolates have been obtained and at least three species, N. frontalis, N. patriciarum and N. hurleyensis have been classified (Heath et al. 1983; Orpin and Munn 1986; Webb and Theodorou 1991). The original classification of these species used classical taxonomy whereby morphological characteristics were used to identify the genus and zoospore ultrastructure was used for the species recognition. Brookman et al. (2000) under took a molecular characterization of the gut fungi based on ribosomal ITS1 and 18S rRNA. Their analysis revealed that N. hurleyensis and N. frontalis were very similar, but that they differed from N. patriciarum. From a morphological perspective the genus Neocallimastix contains species of strictly anaerobic fungi characterized by a monocentricthallus, which consists of a network of branched, tapering rhizoids devoid of nuclei. The zoosporangia are variable, often oval or sphaerical in shape supported on a sporangiophore developed from one or more main rhizoids. As the life cycle of a monocentric fungus is determinate (finite), each thallus (the rhizoidal network) supports just one zoosporangium. Zoospores are uninucleate, and either monoflagellated or often polyflagellated.

Species