Rhynchogastrema coronata
Rhynchogastrema coronata B. Metzler & Oberw. 1989, in Metzler et al., Systematic and applied microbiology, 12(3), 280-287 (1989).
Etymology: coronata (Lat.) - crowned, wreathed.
Diagnosis: In axenic culture, R. coranata develops a loosely interwoven hyphal mat which finally forms irregular strings of synnematous appearance. Hyphae dikaryotic, thin-walled, smooth, hyaline, not gelatinous, mostly 2.5-4 (-5) µm wide, with clamps (Figure 1-5). Septa with dolipores and parenthesomes comprising cup-shaped vesicles of the Tremella-type (Figure 11-13). Typical haustoriaI branches are formed consisting of a sphaeroidal basal part of c. 2 µm in diameter and a slender distal part of c. 0.5 X 5-12 µm. Usually they originate from clamp connections (Figure 1,3), but also from intercalary positions (Figure 10). In the presence of a potential fungal host the haustoria fuse with it (Figure 9). Basidia often in clusters, arising from clamps; basidium with a basally swollen probasidium, distally tapering into a neck of variable length, in total 5-7 x 15-30 µm; apex of the neck partly cruciately septate; septa extending only 1-3 µm backwards into the neck (Figure 2c, 3, 7, 8). Basidiospores sessile, mostly 4, rarely 1-6, each originating from one of the apical neck segments, exceptionally in lateral positions, maturing globose, 2-3 µm in diam., thick walled, wall yellow to brown, irregularly warted, warts blunt. During spore maturation yellowish-brown, persistent exudate is produced which surrounds the spores, often glueing them together as tetrads of 4-7 µm in diameter. Mature spores remain attached to old basidia. Spores germinate readily on moist substrates. The germ tube often breaks through beside the apiculus (Figure 16). On MEA, the monokaryotic stage starts often with a primary vesicle (Figure 14, 17 left, 23a, d, e), from which a yeast colony may originate. Yeast cells are ellipsoidal to fusiform or cylindroidal (Figure. 20, 21, 24). They often sprout along with a more or less pronounced mycelium of an irregular diameter, which easily fragments (Figure 20, 21). The yeast cells are encapsuled with mucilage which appears filamentous in TEM (Figure 16, 22). If, as usual, two or more spores of a tetrad germinate simultaneously, the germ tubes fuse spontaneously and clamped hyphae of a more or less regular diameter start to grow (Figure 15, 18, 23b, c, e). Crossing compatible yeast strains results in formation of clamped mycelium (Figure 25). The compatibility system was not identified. Mycelia and yeasts grow well at room temperature but scarcely at 5° and not at 37°C during two weeks. In contrast to the known taxa in the Tremellales, R. coronata has a unique basidial morphology. Also warted and pigmented basidic spores are not known in any other taxon of this order. Therefore, a new family is proposed to accommodate the genus.
Index Fungorum Number: IF280175
Figure 1-4. Different stages of basidial development and hyphae;H: Haustorium, N: Nucleus. (1) Young basidial stages, Probasidia after karyogamy (arrows). (2) Basidial development. a: Young basidium before spore differentiation; b, c: Partial apical longitudinal septation; d, e: Formation of young spore initials; f: Mature basidium with ornamented spored and basidial outgrowths below. (3, 4) Different stages of basidial development, partly with mature spore tetrads. (4) (left): Yeast cells. Scale bar = 10 µm.
Figure 5-8. (5,6) Groups of basidia in different developmental stages; spore initials (arrows); mature spore tetrads are often surrounded by a solidifying droplet of sticky, pigmented material. LM. Scale bar = 10 µm. (6) Basidial ventres partly stained with cotton blue. Insert: mature spore tetrad. (7) Spore initials with multilayered walls (arrowheads); partial longitudinal septation (large arrow). TEM. Scale bar = 2 µm. (8) Mature basidium with thick-walled ornamented spores; longitudinal septation (arrow). TEM. Scale bar = 2 µm.
Figure 9-13. (9) Rhynchogastrema coronata growing along with Penicillium hordei (P) obviously attacking it with haustoria (H). LM. (10) Haustorium inserted at a clamped hypha. TEM. Scale bar = 2 µm. (11-13) Dolipores with cup shaped parenthesomal elements. TEM. Scale bars = 0,5 µm.
Figure 14-22. (14) Simultaneously germinating tetrads of basidiospores. (15) Fusion of neighbouring germ tubes. LM. (16) Longitudinal section through a germinating spore tetrad; germ tubes covered with fibrous mucilage (arrows); apiculi (arrows) and basidial remnants below. TEM. Scale bar = 2µm. (17) Growth of both haploid (left) and dikaryotic, clamped hyphae (right); after fusion, the left part probably slipped out of the sporal wall. LM. Scale bar = 10 µm. (18) Growth of dikaryotic, clamped hyphae evidently as a result of a previous plasmogamy immediately below the spore tetrade. LM. (19) Primary haploid colony derived from basidiospores, 24 h after germinating on malt extract agar. LM. (20,21) Established two-week-old yeast colony on malt extract agar. LM. (22) Yeast cells with a coat of fibrillar mucilate. TEM. Scale bar = 5 µm.
Figure 23-25: (23) Different stages of germination of spore tetrads. a, d, and e grown on malt extract agar, band c from synthetic nutrient agar. a: vesiculate primary germ tubes; b, c: fusion of two germ tubes and subsequent formation of a clamped hypha; e: both haploid (above) and dikaryotic phase (below) growing from one tetrad. (24) Yeast cells. (25) Artificial crossing: Fusion of two compatible haploid mycelia (arrow at the probable fusion site) and subsequent growth of clamped mycelium.
Reference:
Metzler, B., & Oberwinkler, F., & Petzold, H. (1989). Rhynchogastrema gen. nov. and Rhynchogastremaceae fam. nov.(Tremellales). Systematic and applied microbiology, 12(3), 280-287.
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