Transmission electron microscopy of annellides and conidiogenesis in the synnematal hyphomycete Trichurus spiralis

Abstract

This study was done to compare events of conidiogenesis with previous studies done on the closely related genera Doratomyces and Scopulariopsis. Formation of the first conidium by a T. spiralis annellide was not observed. Conidial initials blew out through the annellide apex, increased in size, and were eventually delimited by centripetally developing septa. Each conidial-delimiting septum subsequently split; the distal layer formed part of the conidial base, and the proximal layer became a portion of the wall of the next conidial initial. A circumscissile rupture of the wall layer continuous between conidium and annellide produced the characteristic annellations and conidial basal frills. Annellations on T. spiralis were more conspicuous than on the two species of Doratomyces and the two species of Scopulariopsis previously studied with electron microscopy. Differences in nuclear behavior and other differences and similarities among the five species were discussed. The term holoblastic to describe conidiogenesis in annellides was questioned.

Phylogeny and taxonomic revision of Microascaceae with emphasis on synnematous fungi

“…It is also morphologically similar to Cephalotrichum and Doratomyces , but distinguished by the presence of setae on the upper part of the synnemata ( Morton & Smith 1963 ). However, detailed ultrastructural studies on the synnematal morphogenesis suggested that the sole presence of setae might not support their distinction as a different genus ( Hasselbring, 1896 , Swart, 1964 , Hammill, 1977 , Abbott, 2000 ). Abbott (2000) studied a large set of strains belonging to these fungi and concluded that the three genera were congeneric, which led to numerous proposed new combinations, but they were not formally published.…”

Ultrastructure of Conidiogenesis in Sphaerostilbe ochracea

“…This appears to be characteristic of noncatenulate forms. A delimiting septum with the same thin attachment characteristics of conidia of S. ochracea is also seen in Neurospora crassa (Lowry, Durkee and Sussman, 1967), Trichoderma saturnisporum (Hammill, 1974), Metarrhizium anisopliae (Hammill, 1972), and Sclerotinia fructicola (Willetts and Calonge, 1969). In catenulate species, however, the septum thickens greatly and forms the connective between adjacent conidia in the chain (Hanlin, 1976;Zachariah and Fitz-James, 1967).…”

“…In S tilbo tham-Ilium nu dipes Haum . (Roquebe rt and Abad ie , 1973) and H arp ographium co ngestum (Berk & B r. ) Deighton (Deighto n, 1974) co nid ium fo rmat ion is ph ialogenous ; in Dora to myces (Hammill, 1972), Graphium penicilloides Corda (Cra ne and Schoknecht, 1973), and Trichurus sp iralis Has selbring (Hammill, 1977) it is annelidic ; and in Pesotu m spp. (Crane and Schoknecht , 1973) and Pha eoisaria s pp.…”

“…Profuse ER has been noted in only a few other phialidic forms. In Trichoderma saturnisporum, Hammill (1974) has postulated that the RER in the phialides and conidia may function in mucus production to coat the conidia. If such a system is actually present in phialides and conidia of Sphaerostilbe ochracea, the explanation offered by Hammill may also account for the origin of the mucus in S. ochracea.…”

Mould Identification

“…Comments: Trichurus (80,149) and Cephalotrichum (= Doratomyces) are essentially identical fungi with the exception that Trichurus has setae. Isolates of Trichurus are rarely encountered in the clinical laboratory.…”