Piromyces J.J. Gold et al.
Monoflagellated protozoans found in the rumen were assigned to the genus Piromonas (Liebetanz 1910; Braune 1913). Orpin concluded that these flagellated cells were in fact zoospores of anaerobic fungi (Orpin 1977a). Orpin retained the generic name on the assumption that the fungi he isolated from the sheep rumen were the same as Liebetanz’s ‘protozoans’ (Liebetanz 1910). However, Gold et al. (1988) questioned this assumption because Liebetanz’s isolates were anteriorly flagellated, obtained nutrition by phagocytosis and divided by binary fission, whereas Orpin’s isolates were posteriorly flagellated, rhizoid producing saprobes that did not undergo binary fission. For these reasons, and to stress fungal affinity, Piromonas was renamed Piromyces (Gold et al. 1988). Piromyces appears the most heterogeneous genus among anaerobic fungi, covering up to eight species. Species of Piromyces isolated to date include P. communis, P. mae, P. dumbonica, P. rhizinflata, P. minutus, P. spiralis, P. citronii, P. polycephalus and P. cryptodigmaticus (Gold et al. 1988; Li et al. 1990; Breton et al. 1991; Ho et al. 1993a, b; Gaillard-Martinie et al. 1995; Chen et al. 2002; Fliegerová et al. 2010). While some of these species appear to have morphologically distinct characteristics, relationships with each other and indeed with other gut fungal genera remains unclear. Just one named but uncultured species (P. cryptodigmaticus GQ850355.1, GQ850368.1, and GQ850318.1) has been categorized according to their molecular characteristics (Fliegerová et al. 2010). Piromyces sp. E2 Teunissen et al. (1991) has been sequenced by the JGI and sequence data is available on request. From a morphological perspective the genus Piromyces 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, sphearical, oval or clubshaped and are supported by a sporangiophore, which develops from one or more rhizoids. As the life cycle of the monocentric fungi is determinate (finite), each thallus (the rhizoidal network) supports just one zoosporangium. Zoospores are uninucleate, sometimes bi- or quadri-flagellate (Gruninger et al. 2014). The phylogenetic relatedness of the rhizoidal genera with monoflagellated zoospores (Piromyces and Anaeromyces) is unclear and as observed by Brookman et al. (2000), it seems likely that the genus Piromyces is polyphyletic and in need of reappraisal.

Species