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Pentaster cepaeophilus gen. et sp nov described from surface of empty shells of Cepaea hortensis

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  • Charles University, Faculty of Science (Prague, Czech Republic)

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Pentaster cepaeophilus gen. et sp. nov. (Pezizomycotina inc. sed.) is proposed for a fungus colonizing surface of empty shells of the land snail Cepaea hortensis. The genus is characterised by melanised, multiseptate staurosporous conidia with five arms seceding rhexolytically. The conidia are unique in that two arms form a central axis and three arms stretch from its centre. The morphological similarity to Tripospermum and Tetraposporium is discussed. © 2013 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.
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Nova Hedwigia 2013 Vol. 96 issue 3–4, 495–500
published online March 6, 2013 Article
© 2013 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart, www.borntraeger-cramer.de
Germany. DOI: 10.1127/0029-5035/2013/0086 0029-5035/2013/0086 $ 1.50
Pentaster cepaeophilus gen. et sp. nov. described from
surface of empty shells of Cepaea hortensis
Ondřej Koukol 1* and Dagmar Říhová2
1 Department of Botany, Charles University in Prague, Benátská 2, CZ-128 01 Prague,
Czech Republic
2 Department of Zoology, Charles University in Prague, Viničná 7, CZ-128 44 Prague,
Czech Republic
With 2 gures
Abstract: Pentaster cepaeophilus gen. et sp. nov. (Pezizomycotina inc. sed.) is proposed for a fungus
colonizing surface of empty shells of the land snail Cepaea hortensis. The genus is characterised by
melanised, multiseptate staurosporous conidia with five arms seceding rhexolytically. The conidia are
unique in that two arms form a central axis and three arms stretch from its centre. The morphological
similarity to Tripospermum and Tetraposporium is discussed.
Key words: anamorphic ascomycete, Gastropoda, pentaradiate conidia, alder alluvial forest.
Introduction
Staurosporous hyphomycetes are typical colonizers of decaying leaf litter from plants
growing along streams with running water (Mueller et al. 2004). Their conidia are
mostly formed by four stretched arms (tetraradiate conidia) that ensure attachment to
a substrate by at least three points. The conidium in this position is quickly and firmly
attached to the substrate before germination (Kendrick 2003).
Rarely, these fungi were also recovered from rainfall collected beneath canopies of
mature forests or from rain-washed tree trunks at localities far from streams (Mueller
et al. 2004). In our study, a distinct staurosporous hyphomycete was found on empty
shells of Cepaea hortensis (O.F.Müller, 1774) (nomenclature according to Horsák et
al. 2010) cultivated on litter from alder alluvial forest during an experimental study
*Corresponding author: ondrej.koukol@natur.cuni.cz
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of microfungi associated with empty gastropod shells (Říhová & Koukol, unpubl.
results). The litter was not cultivated underwater nor was a well-aerated stream in
close vicinity to the sampling locality.
Conidia of this fungus differ in a number of features from conidia of known genera
and therefore a new genus is proposed to accommodate the studied fungus.
Material and methods
Litter from alder alluvial forest was collected in Benešův Luh forest (48°46'39.3"N, 13°51'59.5"E,
430 m a.s.l.) between Bratronice and Chyňava (Czech Republic). The litter was periodically
flooded from a nearby mesotrophic brook before sampling for the experiment. For the purpose of
this experiment, shells of Cepaea hortensis were collected in The Botanical Garden of the Charles
University in Prague (Czech Republic), but this gastropod species occurs naturally in Benešův Luh
forest (D.Říhová, personal observation).
Litter with empty shells was placed into glass Petri dishes (16 cm in diam.) and kept at 15/16°C
day/night regime in dark. The fungus was observed after 4 months of cultivation on the surface of
several shells. Attempts to isolate the fungus into pure culture were not successful. Conidia picked
by a sterile needle under a dissecting microscope and placed on various natural agar media were
overgrown by contaminating microfungi.
For light microscopy, fungal structures were mounted in Melzer’s reagent and examined with
differential interference contrast (Olympus BX–51 with digital camera). Pictures were further
enhanced using the Helicon Focus and Adobe Photoshop programs. Microscopic measurements are
reported as the mean ± standard deviation (values of 20 measurements). The holotype specimen is
deposited in PRM (Herbarium of the Prague National Museum, Czech Republic).
Taxonomy
Pentaster Koukol gen. nov.
Mycobank Accession Number: MB 564336
Etymology: Pentaster = referring to the overall appearance of conidia resembling a star with five arms.
Anamorphic fungus, hyphomycete, saprotrophic. On the natural substrate mycelium
superficial, conidiophores micronematous. Conidiogenous cells terminal. Conidia
solitary, pentaradiate, multiseptate, composed of main axis and three arms, arms
stretching from the centre of the main axis, straight, tapering. Conidia secede
rhexolytically.
SpEciES typica: Pentaster cepaeophilus Koukol sp. nov., see below.
Pentaster cepaeophilus Koukol, sp. nov. Figs 1–2
Teleomorph – anamorph connection: unknown.
Mycobank Accession Number: MB 564337
Vegetative hyphae brown, septate, 4.5–9 µm wide, forming a loose network on the
surface of the substrate. Conidiogenous cells determinate, monoblastic, terminal,
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5–7 µm wide. Conidia pentaradiate, dark brown in the middle, paler towards the
base and the tip. Central axis straight, reaching (98.5)107–136(160) µm length and
(10)11.5–15.5(17.5) µm width in the middle, 7–10-septate. Three arms stretching in
plane approximately orthogonal to the conidium axis from the middle cell, straight,
(35)47–62(70) µm long and (7.5)9.5–12(14) µm wide at the base, 3–5-septate. Apical
cells of the central axis and arms hyaline to subhyaline, tapering towards 2.5–5.5 µm.
Conidia germinate from terminal cells of each of the arms with hyaline hyphae 2.5–3.5 µm
wide.
HolotypuS: On surface of empty shell of Cepaea hortensis on litter from alder alluvial forest
sampled in Benešův Luh forest between Bratronice and Chyňava (Czech Republic), 30 Nov 2011,
leg. O.Koukol & D.Říhová (PRM899945).
Etymology: cepaeophilus = referring to the substrate, gastropod of the genus Cepaea.
Fig. 1. Pentaster cepaeophilus. a. Mycelium with conidia on the shell of Cepaea hortensis. b. Conidia
(some of them germinating from apical cells) and vegetative hyphae. Note the conidium without side
arms (see arrow). c–d. Two mature detached conidia (Bars = 50 µm).
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Discussion
Pentaster cepaeophilus is characterized by production of strictly pentaradiate conidia
that consist of a central axis and three arms stretching from its centre. The conidium
is symmetrical along a mirror plane cutting through the centre of the central axis and
one arm. Microfungi forming strictly or predominantly pentaradiate conidia are rather
rare compared to the more common tetraradiate shape. Batista (1957) described the
monotypic genus Pentaposporium that was characterised by pentaradiate conidia
formed on erect conidiophores. According to the protologue, conidia of P. furcoryae
Bat. reached the same dimensions as conidia of P. cepaeophilus, but were produced
on erect conidiophores and were constricted at the septa (Batista 1957). We did
not study the type collection, but we incline to the opinion of Hughes (1976), who
considered the species to belong to Tripospermum based on the dominant presence
of tetraradiate conidia and phialides of the Phialophora-like synanamorph in the
type collection. Pentaradiate conidia present in the collection most probably resulted
from aberrant division of the conidium (Hughes 1976). Dwayaangam quadricauda
(Drechsler) Subram. also produces conidia that at maturity have five arms, but they
are hyaline and have a completely different symmetry (Drechsler 1961). Various other
species forming predominantly tetraradiate conidia may occasionally produce conidia
with five arms, such as Qaudricladium aquaticum Nawawi & Kuthub. (Nawawi &
Kuthubutheen 1989) or Tulipispora ingoldii Révay & Gönczöl (Révay et al. 2009),
but they are all hyaline and their arms are constricted at the base. Among species with
melanised conidia, in Tripospermum four arms typically stretch from two central cells,
but conidia with prolonged stalk cells, such as at T. myrti (Lind) S. Hughes, may be
considered as pentaradiate (Matsushima 1975). Nevertheless, Pentaster differs from
Tripospermum in the symmetry of conidia and presence of the central axis.
Fig. 2. Mature detached conidium of Pentaster cepaeophilus (Bar = 50 µm).
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The absence of distinct conidiophores and production of terminal multiradiate brown
conidia shows morphological similarity to Tetrabrunneospora, but conidia in this genus
are strictly tetraradiate. Their shape results from growth of a primordium in one axis,
its septation followed by elongation and septation of the distal cell in three axes (Dyko
1978). It is not known whether the three arms of P. cepaeophilus grow from the central
cell simultaneously with the axis, or the axis is first formed and then the central cell
produces three lateral arms. The latter would be supported by rare presence of conidia
without lateral arms (Fig 1b). On the other hand, these conidia may be aberrant.
Pentaster resembles also Tetraposporium that has integrated conidiogenous cells and
one arm of the conidium is stretched in its axis, but the conidiogenous cell is denticulate
and conidia are only tetraradiate (Ellis 1971).
Setae that occur on the subiculum of some ascomycetes (Crassochaeta, Réblová
1999) and basidiomycetes (Asterostroma, Suhara et al. 2010) may be also similar to
staurospores and brown to dark brown. However, setae in these genera are variable in
number of branches, nonseptate and never germinate as conidia.
Conidia of Pentaster are released rhexolytically, each conidium has a remnant of the
conidiogenous cell on the basal cell of the central axis (Fig. 2). Though conidia did not
germinate on agar plates, we observed germination of conidia on the substrate (Fig.
1b). Apical cells of one or several arms simultaneously produced hyaline mycelium.
This confirms the role of the arms in attachment to the substrate (Kendrick 2003).
Pentaster cepaeophilus seems to have a substrate affinity towards the proteinaceous
material or the calcareous microstructures present in gastropod shells. Mycelial nets
with conidia were found on about 20 shells resting on the litter. Sterile brown mycelium
probably belonging to P. cepaeophilus was observed also on the litter particles, but
no conidia were visible under the dissecting microscope to confirm the connection.
Acknowledgements
We thank to Dr. David Minter and Dr. Ludmila Marvanová for valuable comments on the fungus.
This study was supported by the Grant Agency of the Charles University in Prague (project no.
62109) and by the grant SVV-2012-265 206.
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Novos géneros e espécies de fungos imperfeitos
  • A C Batista
BATISTA, A.C. 1957: Novos géneros e espécies de fungos imperfeitos. -Rev. Biol. 1: 97-112.
Some clampless hyphomycetes predacious on nematodes and rhizopods
DRECHSLER, C. 1961: Some clampless hyphomycetes predacious on nematodes and rhizopods. – Sydowia 15: 9–25.