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Longevity of light- and dark-colored basidiospores from saprotrophic mushroom-forming fungi

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Abstract

Fungi can produce resistant propagules that may last for decades. Basidiospores from ectomycorrhizal fungi had been experimentally shown to last for at least 6 yr, but there are few reports on the longevity of saprotrophic members of mushroom-forming fungi. Here, the author shows evidence of spore longevity of these fungi by collecting, drying, storing, and germinating these spores over time. Results showed that dark-colored spores have a much-extended longevity as compared to light-colored spores. Dark-colored spores of some species are viable to at least 2.8 yr, whereas light-colored spores are generally viable for a much shorter period of time. The author proposes that mushroom-forming basidiomycete fungi employ two different ecological strategies: one with extended longevity that allows for long-distance dispersal, and the other takes advantage of optimal conditions that support both mushroom formation, basidiospore dispersal, and germination locally.
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Mycologia
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Longevity of light- and dark-colored basidiospores
from saprotrophic mushroom-forming fungi
Nhu H. Nguyen
To cite this article: Nhu H. Nguyen (2018) Longevity of light- and dark-colored basidiospores from
saprotrophic mushroom-forming fungi, Mycologia, 110:1, 131-135
To link to this article: https://doi.org/10.1080/00275514.2017.1401390
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Published online: 04 Jun 2018.
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Longevity of light- and dark-colored basidiospores from saprotrophic
mushroom-forming fungi
Nhu H. Nguyen
Department of Plant and Soil Sciences, University of HawaiʻiatMānoa, Honolulu, Hawaii 96922
ABSTRACT
Fungi can produce resistant propagules that may last for decades. Basidiospores from ectomycor-
rhizal fungi had been experimentally shown to last for at least 6 yr, but there are few reports on
the longevity of saprotrophic members of mushroom-forming fungi. Here, the author shows
evidence of spore longevity of these fungi by collecting, drying, storing, and germinating these
spores over time. Results showed that dark-colored spores have a much-extended longevity as
compared to light-colored spores. Dark-colored spores of some species are viable to at least 2.8 yr,
whereas light-colored spores are generally viable for a much shorter period of time. The author
proposes that mushroom-forming basidiomycete fungi employ two different ecological strategies:
one with extended longevity that allows for long-distance dispersal, and the other takes advan-
tage of optimal conditions that support both mushroom formation, basidiospore dispersal, and
germination locally.
ARTICLE HISTORY
Received 1 June 2017
Accepted 2 November 2017
KEYWORDS
Dispersal; dormancy;
longevity; melanin;
mushroom; saprotrophs;
spore; viability
INTRODUCTION
Spores are a means for fungi to overcome dispersal bar-
riers and escape their current environment to propagate
on newer and more favorable habitat. The importance of
mushroom-forming basidiomycetes and their basidios-
pores had not been overlooked. The work of Nils Fries
and others that culminated in the 1980s shed much light
into germination cues in both mutualistic and sapro-
trophic basidiomycete species (Fries 1984). Continued
research contributed to the mechanisms of spore germi-
nation and longevity (Fortin 1990; Miller et al. 1993;
Torres and Honrubia 1994; Martín and Gràcia 2000;
Lagrangel et al. 2001; Kikuchi et al. 2007;Peayetal.
2009), and how these factors affected the ecology of basi-
diomycete fungi, their hosts, and their environments
(Aime and Miller 2002; Ashkannejhad and Horton
2006; Ishida et al. 2008; Bruns et al. 2009;Nara2009;
Nguyen et al. 2012;Peayetal.2012).
More specifically, longevity and dormancy of fungal
spores has received prolonged interest among mycolo-
gists. Experimental evidence for ectomycorrhizal fungal
spores had been reported to have a longevity of up to 6
yr (see Nguyen et al. 2012 and references therein),
whereas reports of longevity for saprotrophic fungi,
although rare, may periodically be found as side notes
sprinkled deep within various research papers. For
example, saprotrophic fungal spores had been reported
to have short longevity of several days in Fomes igniar-
ius var. populinus (Good and Spanis 1958) to several
years in Calvatia gigantea (Bulmer and Beneke 1962)
and more than 9 yr in Psilocybe mutans (Sussman and
Halvorson 1966). Some species, such as Lycoperdon
pusillum (Bulmer and Beneke 1964), Polyporus tomen-
tosus (Whitney 1966), Crepidotus spp. (Aime and Miller
2002), and Rhizopogon spp. (Bruns et al. 2009), exhib-
ited endogenous dormancy where an increasing num-
ber of spores break dormancy and become viable over
time. However, spores in general whether stored at
room temperature or frozen in cold storage appear to
eventually encounter an end to their longevity (Fries
1984; Banerjee and Sundberg 1993; Torres and
Honrubia 1994).
Alongside spore dormancy and longevity, character-
istics such as germinability, ornamentation, wall thick-
ness, hydrophobicity, and pigmentation appear to be
important ecological traits for both ectomycorrhizal
and saprotrophic basidiomycetes (Fries 1984,1987;
Halbwachs and Bässler 2015; Halbwachs et al. 2015).
Thick walls can provide protection from harsh envir-
onmental conditions such as dessicating air and animal
digestive tracts (Garnica et al. 2007), whereas pigmen-
tation/melanization of the spore walls can provide sub-
stantial protection from physical, biological, and
chemical damage, including ultraviolet (UV) radiation
CONTACT Nhu H. Nguyen nhu.nguyen@hawaii.edu
Supplemental data for this article can be accessed on the publishers Web site.
MYCOLOGIA
2018, VOL. 110, NO. 1, 131135
https://doi.org/10.1080/00275514.2017.1401390
© 2018 The Mycological Society of America
Published online 04 Jun 2018
(Durrell 1964; Sussman and Halvorson 1966; Kuo and
Alexander 1967; Hawker and Madelin 1976; Rehnstrom
and Free 1996; Ulevičius et al. 2004; Vellinga 2004;
Cordero and Casadevall 2017). Overall, pigmented
and thick-walled spores appear to be an advantage for
pioneer species that need to be able to resist hazardous
environments prior to landing on a suitable substrate
for germination (Halbwachs et al. 2015), and it was
suggested that, although not immediately clear, the
opposite is true for non- or lightly pigmented spores
with thin walls. Below, I report on the longevity of
saprotrophic agaric basidiomycete spores over 5 yr
and focus discussion of their longevity in the context
of spore pigmentation or the lack thereof.
MATERIALS AND METHODS
Mushrooms of 43 species were collected from various
locations in coastal northern California starting in
January 2010 to January 2012 and identified using
morphological characteristics. As many mushrooms
were collected from a single location as possible and
brought back to the laboratory where spores were
allowed to drop onto aluminum foil overnight. Spore
prints that were thin and appeared to have been con-
taminated with excess liquid or those with insect larval
trails were discarded. Collections of a species that had
fewer than three good prints remaining were not used
further, resulting in collections with three to four prints
for each species. In a few cases, a single species may be
collected more than once from different localities
(SUPPLEMENTARY TABLE 1).
Spore prints were classified as light (white to off-
white), medium (pink), and dark (light brown to black)
spore color for ease of discussion. To measure the
blackness, or darkness, value of a spore, photographs
of spore prints were made using a constant light source
and identical digital camera settings. The images were
imported into Adobe Photoshop where their hue,
saturation, and lightness values (HSL; sometimes writ-
ten as HSB) were determined, and the blackness values
were extracted for further analyses. Each image was
subsampled 10 times to determine the average darkness
of the spores, measured from 0 = completely white to
100 = completely black.
To measure absorbance of the melanin present in
the spores, each species was diluted to 10,000 spores
per milliliter in deionized water with 2% ethanol, and
the 329 nm absorbance was measured using a Jenway
6405 spectrophotometer (Keison International, Essex,
UK). The absorbance spectrum of 329 nm was used
because it fits within the absorbance spectrum of fungal
melanins, in particular Schizophyllum commune (Arun
et al. 2015) melanins and those found in the spores in
this study.
For viability assays, a sterile toothpick was used to
score across a spore print, which was then inoculated as
a single point on an agar plate. Spores were inoculated on
day 1 as soon as the prints were ready before the spores
had a chance to dry out. Once inoculated, the spores were
air-dried and kept in parafilm sealed Petri dishes at 25 C,
<50% relative humidity, and no light exposure for long-
term storage. The prints were inoculated at an interval of
once every 3 mo for up to 1 yr, and after that every 6 mo
for 2 more yr. Spores were assayed once more after 5 yr. If
a species lost viability during the assay period, it was
inoculated once more during the next period to make
sure that the observations were accurate. Due to time
constraints, exact longevity end point could not be
assessed for all species and is marked with an asterisk (*)
in SUPPLEMENTARY TABLE 1.
Spores were assayed for germination and hyphal
growth on 2% malt extract agar, which is a standard
medium for growing many fungi and have been routi-
nely used for spore germination assays over the last
century (Fries 1984). Plates were incubated at 25 C
for 7 d. Plates that showed no hyphae were further
incubated up to 1 mo. Antibiotics were not used, and
bacterial contamination was infrequent. Plates contami-
nated with common aerially dispersed anamorphic
fungi such as Penicillium and Cladosporium could
easily be identified and discarded. For a collection to
qualify as viable, at least one half of the spore prints
must show positive growth of what appears to be basi-
diomycete hyphae germinated from basidiospores;
otherwise, the assay was recorded as nonviable.
Approximate date to germination was also recorded
(SUPPLEMENTARY TABLE 1).
To test whether light-colored spores lost their viabi-
lity due to drying, spore prints of five species were
collected and half were stored dry as above and the
other half were stored in moist chambers at 12 C with
relative humidity near saturation. Spores of moist-
stored spores were assayed as above along with their
dried counterparts.
RESULTS
Spores of 25 species (58%) germinated readily on 2%
malt extract agar, whereas those of 18 species (42%) did
not. Germination can be rapid (within 24 h), as in
Hypholoma fasiculare, Psathyrella candolleana, and
Prunulus (Mycena)purus, or may be delayed to over 7
d, as in Agaricus xanthodermus or Clitopilus prunulus.
However, most spores germinated within 7 d of inocu-
lation (SUPPLEMENTARY TABLE 1). Since each
132 NGUYEN: LONGEVITY OF SAPROTROPHIC MUSHROOM SPORES
collection came from a single genet, replicate mush-
rooms behaved similarly in terms of germination time
and longevity. Of the light spores, 56% of the species
did not germinate, of the medium spores 80% of the
species did not germinate, and of the dark spores 26%
of the species did not germinate.
Lighter-colored spores tend to have a shorter long-
evity than dark-colored spores (FIG. 1). The trend was
statistically significant for both spore darkness (P<
0.0001, R
2
= 0.536) and spore absorbance at 329 nm
(P< 0.0001, R
2
= 0.564). Many light-colored spores
have a short longevity that was less than 91 d (3 mo),
with the exception of three species: Pleurotus ostreatus
and Armillaria nabsnona with a longevity up to 91 d
and Flammulina velutipes with a longevity up to 183 d
(6 mo). Only one species of the medium-colored (pink)
spore species, C. prunulus, germinated, but its longevity
was less than 91 d. The dark-colored spores tended to
have the longest longevity, up to 1004 d (2.8 yr),
although there was a broad spread starting from at
least 91 d. None of the basidiomycete species in this
study had spores that were viable after 5 yr, although
spores of contaminating anamorphic ascomycetes such
as Penicillium and other species with black spores
remained viable.
Moist storage did not seem to affect the viability of
light-colored spores, although only two of the five
species treated this way germinated. Spores stored in
both dry and moist conditions were equally viable after
91 d for A. nabsnona and 183 d for F. velutipes.
DISCUSSION
Somewhat contrary to the results of spore germination
studies in earlier works that reported easy germination
on many saprotrophic basidiomycetes (Fries 1984), a
large proportion of the collections in this study did not
germinate. Since germination was done only on 2%
malt extract agar, some complex environmental para-
meters that control germination probably had been
overlooked. A more complex medium set that contains
additives such as yeast extract (Banerjee and Sundberg
1993) or lignocellulose substrates or extracts (Wall and
Kuntz 1964; Whitney and Bohaychuk 1971), as well a
proper pH (Fries 1984) and lowered concentrations of
inhibitors such as ammonium (Fries 1949), may be
more advantageous to germinating some of the species
that failed to germinate here. Some species may require
cold stratification (Denver 1960), heat shock (Chang
and Chu 1969), or co-cultivated with activator organ-
isms(Fries 1984,1987) to induce germination.
However, the representative 58% that germinated still
provided important insights into the longevity of
mushroom-forming basidiomycetes.
Spores of these diverse mushroom-forming basidio-
mycetes can have drastically different germination stra-
tegies. Some species such as Marasmius and Mycena
spp. can germinate within several hours (Fries 1949,
1984), others such as Corpinus quadrifidus and
Conocybe lactea can germinate within a day over sev-
eral days (Miller et al. 1993), whereas some Crepidotus
spp. may require up to 45 wk to germinate (Aime and
Miller 2002). Germination of some species in this study
started within 24 h (probably within a few hours of
inoculation), whereas some others started over 7 d.
These numbers fit within the reported range.
Crepidotus mollis was used in this study, but observa-
tions stopped at 12 wk due to no germination. This
period falls a few weeks short of the typical time it takes
for members of this genus to germinate (Aime and
Miller 2002). Since germination was determined from
1 d followed by 3-mo intervals, some fine-scale viability
measurements of some species could not be deter-
mined. Germination times of those spores that
0 200 400 600 800 1000
10 20 30 40 50 60 70 80
Longest observed viability (days)
Spore darkness
A
0 200 400 600 800 1000
0.00 0.01 0.02 0.03 0.04
Longest observed viability (days)
Spore absorbance (329 nm)
B
Figure 1. A, B. Linear regression analyses of spore darkness (A) and absorbance at 329 nm (B) versus spore viability over time. The
results show significant trends in both. A. P< 0.0001, R
2
= 0.536. B. P< 0.0001, R
2
= 0.564.
MYCOLOGIA 133
remained viable up to the 3-mo interval were reported
as 1 d in SUPPLEMENTARY TABLE 1. This coarse-
ness, along with time constraints that prevented obser-
vations of longevity until end point of all the
germinated species, likely contributed to the spread of
the data in FIG. 1.
In general, lighter-colored spores exhibited a much
shorter longevity than dark-colored spores. Spore wall
chemistry such as hydrophobicity, thickness, and pig-
mentation appeared to be connected to longevity. All of
the light-colored spores in this study were hydrophilic
and aggregated into a translucent mass upon drying (it
was necessary to moisten the area of interest on the
spore print with sterile water before the spores will
come off the aluminum foil). Medium and dark spores
were hydrophobic (fluffier) and could be scraped off
the foil with ease. The high proportion of nongermin-
able light- (56%) and medium- (80%) versus dark-
(26%) colored spores on a single agar medium may
reflect the idiosyncratic requirements for specific con-
ditions that are available locally. Following this idea,
these light- and medium-colored spores do not need to
travel far, and without the need for long-distance travel,
these spores were not built to last a long time. Their
thin walls may equate to less energetic requirements
under nutrient constraints of plant cellulosic composi-
tion, and the hydrophilic nature of the walls would
allow them to easily attach to locally moist substrates.
This is opposed to dark-colored spores that do travel
and thus have hydrophobic walls that allow them to
resist sticking to local substrates and withstand adverse
environmental conditions such as predation and UV
radiation (Durrell 1964; Sussman and Halvorson 1966;
Kuo and Alexander 1967; Hawker and Madelin 1976;
Rehnstrom and Free 1996; Ulevičius et al. 2004;
Vellinga 2004; Lilleskov and Bruns 2005; Cordero and
Casadevall 2017) and thus can remain viable for a
much longer period of time. Apart from these hypothe-
sized mechanisms, others that may be just as important
in maintaining longevity remain to be discovered.
From these general results, I propose that mush-
room-forming basidiomycete fungi employ two dif-
ferent ecological strategies: one that takes advantage
of long-distance dispersal and environmental resis-
tance, waiting for the optimal conditions for spore
germination, and the other that takes advantage of
the locally optimal, and perhaps ephemeral, condi-
tions that support both mushroom formation, basi-
diospore dispersal, germination, and mycelial
establishment. Light-colored spores germinate imme-
diately upon landing on their proper substrate during
environmental conditions that are conducive to ger-
mination and hyphal extension. Dark-colored spores
may also take advantage of immediate germination
(such as those with germ pores), but they also could
rely on their ability to resist adhering to a substrate
upon drying and have a slightly better chance to
disperse to another location. Having an extended
longevity would enable these spores to remain viable
during long-distance dispersal. These hypotheses are
testable and await further work.
ACKNOWLEDGMENTS
I thank Meredith Blackwell for turning me into a mycologist.
My undergraduate research career was just as a spore written
in this paper, germinating into a bewildering world of
research. Without Merediths firm support and keen direc-
tion to tune my multidirectional interest in many things
biological, I fear that I would currently be pressing plants
or pinning insects in an isolated corner of a natural history
museum. I am grateful to have the chance at a longevity
devoted to studying fungi. I thank Else Vellinga for assistance
with identification of some species of mushrooms, under-
graduate Jonathan Abe for measuring spore absorbance, as
well as the two anonymous reviewers who provided great
advice for improving the manuscript.
FUNDING
This work was supported in part by the NSF-GRFP to N.H.N.
ORCID
Nhu H. Nguyen http://orcid.org/0000-0001-8276-7042
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MYCOLOGIA 135
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... This reveals an extraordinary capacity for Podaxis spores to remain viable, despite prolonged periods without moisture, and suggests that spores could remain dormant in the environment for centuries before germinating once conditions allow. The dark spore pigmentation in Podaxis (Figures 1A and S2; Table S8) (Conlon et al., 2016) indicates heavy melanization, likely providing protection from environmental stressors (Eisenman et al., 2020), as melanization is known to positively correlate with spore longevity in basidiomycetes (Nguyen, 2018). ...
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Insights into the genomic consequences of symbiosis for basidiomycete fungi associated with social insects remain sparse. Capitalising on viability of spores from centuries-old herbarium specimens of free-living, facultative and specialist termite-associated Podaxis fungi, we obtained genomes of 10 specimens, including two type species described by Linnaeus >240 years ago. We document that the transition to termite associations was accompanied by significant reduction in genome size and gene content, accelerated evolution in protein-coding genes, and reduced functional capacities for oxidative stress responses and lignin degradation. Functional testing confirmed that termite specialists perform worse under oxidative stress, while all lineages retained some capacity to cleave lignin. Mitochondrial genomes of termite associates were significantly larger, possibly driven by smaller population sizes or reduced competition, supported by apparent loss of certain biosynthetic gene clusters. Our findings point to relaxed selection that mirrors genome traits observed among obligate endosymbiotic bacteria of many insects.
... This reveals an extraordinary capacity for Podaxis spores to remain viable, despite prolonged periods without moisture, and suggests that spores could remain dormant in the environment for centuries before germinating once conditions allow. The dark spore pigmentation in Podaxis (Figures 1A and S2; Table S8) (Conlon et al., 2016) indicates heavy melanization, likely providing protection from environmental stressors (Eisenman et al., 2020), as melanization is known to positively correlate with spore longevity in basidiomycetes (Nguyen, 2018). ...
Article
Insights into the genomic consequences of symbiosis for basidiomycete fungi associated with social insects remain sparse. Capitalising on viability of spores from centuries-old herbarium specimens of free-living, facultative and specialist termite-associated Podaxis fungi, we obtained genomes of 10 specimens, including two type species described by Linnaeus >240 years ago. We document that the transition to termite associations was accompanied by significant reduction in genome size and gene content, accelerated evolution in protein-coding genes, and reduced functional capacities for oxidative stress responses and lignin degradation. Functional testing confirmed that termite specialists perform worse under oxidative stress, while all lineages retained some capacity to cleave lignin. Mitochondrial genomes of termite associates were significantly larger, possibly driven by smaller population sizes or reduced competition, supported by putative losses of biosynthetic gene clusters. Our findings point to relaxed selection that mirrors genome traits observed among obligate endosymbiotic bacteria of many insects.
... The melanin inhibitor resulted in the release of pigment into culture supernatants and alteration in cell length, suggesting changes in the cell wall due to loss of melanin that affected ability to withstand osmotic stress (Kejžar et al. 2013 (2005) Appl Microbiol Biotechnol correlated with spore viability over a 5-year time period. Spores for the study were collected from field sites in northern California and analyzed for pigmentation and germination on malt agar (Nguyen 2018). ...
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Melanins provide fungi protection from environmental stressors, support their ecological roles, and can confer virulence in pathogens. While the function, structure, and synthesis of melanins in fungi are not fully understood, they have been shown to have varied roles. Recent research has revealed a wide range of functions, from radiation resistance to increasing virulence, shedding light on fungal diversity. Understanding fungal melanins can provide useful information, from harnessing the properties of these various melanins to targeting fungal infections.Key Points • Melanotic fungi are widespread in nature. • Melanin functions to protect fungi in the environment from a range of stresses. • Melanin contributes to pathogenesis and drug resistance of pathogenic fungi.
... But a spore that dies in the atmosphere will have zero fitness, even if it ultimately settles back to the ground, and an equally important facet of successful dispersal is survival. Spores in the atmosphere may survive for days or weeks or possibly longer (31)(32)(33)(34). Careful data tracking the lifetimes of individual spores in the air are lacking; spores are not easy to observe or manipulate in nature. ...
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Fungi disperse spores to move across landscapes and spore liberation takes different patterns. Many species release spores intermittently; others release spores at specific times of day. Despite intriguing evidence of periodicity, why (and if) the timing of spore release would matter to a fungus remains an open question. Here we use state-of-the-art numerical simulations of atmospheric transport and meteorological data to follow the trajectory of many spores in the atmosphere at different times of day, seasons, and locations across North America. While individual spores follow unpredictable trajectories due to turbulence, in the aggregate patterns emerge: Statistically, spores released during the day fly for several days, whereas spores released at night return to ground within a few hours. Differences are caused by intense turbulence during the day and weak turbulence at night. The pattern is widespread but its reliability varies; for example, day/night patterns are stronger in southern regions. Results provide testable hypotheses explaining both intermittent and regular patterns of spore release as strategies to maximize spore survival in the air. Species with short-lived spores reproducing where there is strong turbulence during the day, for example in Mexico, maximize survival by releasing spores at night. Where cycles are weak, for example in Canada during fall, there is no benefit to releasing spores at the same time every day. Our data challenge the perception of fungal dispersal as risky, wasteful, and beyond control of individuals; our data suggest the timing of spore liberation may be finely tuned to maximize fitness during atmospheric transport.
... Spores are thought to be the most important propagules of fungi. External ornamentations like spines, ridges, hooks, etc. are supposed to facilitate ectozoochory, while thick walls and pigmentation are important for endozoochory Calhim et al. 2018) and prolong their vitality (Nguyen 2018). For example, Kobayashi et al. (2017) found that colored spores isolated from the guts of drosophilids found on fruit bodies were less damaged than colorless ones. ...
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Dispersal of mycorrhizal fungi via animals and the importance for the interacting partners’ life history as well as for ecosystems is an understudied topic. In this review, we describe the available evidence and the most important knowledge gaps and finally suggest ways to gain the missing information. So far, 33 articles have been published proving a successful transfer of mycorrhizal propagules by animals. The vast majority of research on invertebrates was focused on arbuscular mycorrhizal (AM) fungi, whereas papers on vertebrates (mainly rodents and artiodactyls) equally addressed ectomycorrhizal (ECM) and AM fungi. Effective dispersal has been mostly shown by the successful inoculation of bait plants and less commonly by spore staining or germination tests. Based on the available data and general knowledge on animal lifestyles, collembolans and oribatid mites may be important in transporting ECM fungal propagules by ectozoochory, whereas earthworms, isopods, and millipedes could mainly transfer AM fungal spores in their gut systems. ECM fungal distribution may be affected by mycophagous dipterans and their hymenopteran parasitoids, while slugs, snails, and beetles could transport both mycorrhizal groups. Vertebrates feeding on fruit bodies were shown to disperse mainly ECM fungi, while AM fungi are transported mostly accidentally by herbivores. The important knowledge gaps include insufficient information on dispersal of fungal propagules other than spores, the role of invertebrates in the dispersal of mycorrhizal fungi, the way in which propagules pass through food webs, and the spatial distances reached by different dispersal mechanisms both horizontally and vertically.
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Although fungal spores are tiny compared to plant seeds, their morphological variability is enormous, which points toward selective forces. We investigated the frequency of ornamentation, thick walls, pigmentation and germ pores of spores of ectomycorrhizal and saprotrophic agarics. We hypothesised that these traits are shaped by the needs of these distinct lifestyles. All traits showed a strong phylogenetic signal; we therefore applied a phylogenetically informed statistical analysis. There was a significantly higher occurrence of spore ornamentation in ectomycorrhizal agarics and a higher occurrence of thick-walled spores in saprotrophic agarics. The interplay between thick-walled and pigmented spores and the occurrence of germ pores was only significant for saprotrophs. We argue that ornamentation is probably important to ectomycorrhizal fungi for dispersal by soil invertebrates, whereas pigmented thick walls and germ pores would be more advantageous for predominantly r-selected saprotrophic agarics exposed to hazardous environments and in need of quick germination success.
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Field mycologists have a deep understanding of the morphological traits of basidiospores with regard to taxonomical classification. But often the increasing evidence that these traits have a biological meaning is overlooked. In this review we have therefore compiled morphological and ecological facts about basidiospores of agaricoid fungi and their functional implications for fungal communities as part of ecosystems. Readers are introduced to the subject, first of all by drawing attention to the dazzling array of basidiospores, which is followed by an account of their physical and chemical qualities, such as size, quantity, structure and their molecular composition. Continuing, spore generation, dispersal and establishment are described and discussed. Finally, possible implications for the major ecological lifestyles are analysed, and major gaps in the knowledge about the ecological functions of basidiospores are highlighted.
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Several, although probably not all, factors affecting germination of basidiospores of C. gigantea have been discussed: 1. Incorporation of 6 mg per liter of Chloromycetin into the germination medium does not appreciably affect the number of spores that germinate and develop into visible colonies. This concentration of Chloromycetin inhibits many of the bacteria normally found in sporophores of C. gigantea. 2. Incubation temperatures of 24–26° C are most suitable for germinating basidiospores of C. gigantea. 3. The number of spores inoculated into each Petri dish affects the germination per million. Although this figure varies from one sporophore to another and appears to decrease as the germination per million increases, from present data a spore concentration of 1.0 to 5.0 × 10⁶ per Petri dish usually results in the greatest germination per million. 4. Storage temperatures of -18° C or +12° C appear to maintain with greater consistency the germination per million as opposed to storage at room temperature. This also varies somewhat between different sporophores. 5. An increase of the germination per million for spores from some sporophores after increased storage time tends to infer an after-ripening period is necessary for spores of C. gigantea. 6. Present data suggest that the germination per million decreases when spores have been stored in excess of 1–2 years. Greater testing of this factor is necessary.
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Patterns of fungal spore dispersal affect gene flow, population structure and fungal community structure. Many Basidiomycota produce resupinate (crust-like) basidiocarps buried in the soil. Although spores are actively discharged, they often do not appear to be well positioned for aerial dispersal. We investigated the potential spore dispersal mechanisms of one exemplar of this growth form, Tomentella sublilacina. It is a widespread ectomycorrhizal fungus that sporulates in the soil organic horizon, can establish from the spore bank shortly after disturbance, but also can be a dominant species in mature forest stands. We investigated whether its spores could be dispersed via spore-based food webs. We examined external surfaces, gut contents and feces from arthropod fungivores (mites, springtails, millipedes, beetles, fly larvae) and arthropod and vertebrate predators (centipedes, salamanders) from on and around T. sublilacina sporocarps. Spore densities were high in the guts of many individuals from all fungivore groups. Centipede gut contents, centipede feces and salamander feces contained undigested invertebrate exoskeletons and many apparently intact spores. DAPI staining of spores from feces of fungivores indicated that 7–73% of spores contained intact nuclei, whereas spores from predators had lower percentages of intact nuclei. The spiny spores often were lodged on invertebrate exoskeletons. To test the viability of spores that had passed through invertebrate guts we used fecal droppings of the millipede Harpaphe haydeniana to successfully inoculate seedlings of Pinus muricata (Bishop pine). These results indicate the potential for T. sublilacina spore dispersal via invertebrates and their predators in soil food webs and might help to explain the widespread distribution of this species. It is likely that this is a general mechanism of dispersal for fungi producing resupinate sporocarps, indicating a need to develop a fuller understanding of the linkages of soil food webs and spore dispersal.
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Melanins are ancient biological pigments found in all kingdoms of life. In fungi, their role in microbial pathogenesis is well established; however, these complex biomolecules also confer upon fungal microorganisms the faculty to tolerate extreme environments such as the Earth's poles, the International Space Station and places contaminated by toxic metals and ionizing radiation. A remarkable property of melanin is its capacity to interact with a wide range of electromagnetic radiation frequencies, functioning as a protecting and energy harvesting pigment. Other roles of fungal melanin include scavenging of free radical, thermo-tolerance, metal ion sequestration, cell development, and mechanical-chemical cellular strength. In this review, we explore the various functions ascribed to this biological pigment in fungi and its remarkable physicochemical properties.
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Melanins are enigmatic pigments produced by a wide variety of microorganisms including bacteria and fungi. Here, we have isolated and characterized extracellular melanin from mushroom fungus, Schizophyllum commune. The extracellular dark pigment produced by the broth culture of S. commune, after 21 days of incubation was recovered by hot acid-alkali treatment. The melanin nature of the pigment was characterized by biochemical tests and further, confirmed by UV, IR, EPR, NMR and MALDI-TOF Mass Spectra. Extracellular melanin, at 100 μg/ml, showed significant antibacterial activity against Escherichia coli, Bacillus subtilis, Klebsiella pneumoniae and Pseudomonas fluorescens and antifungal activity against Trichophyton simii and T. rubrum. At a concentration of 50 μg/ml, melanin showed high free radical scavenging activity of DPPH (2,2-diphenyl-1-picrylhydrazyl) indicating its antioxidant potential. It showed concentration dependent inhibition of cell proliferation of Human Epidermoid Larynx Carcinoma Cell Line (HEP-2). This study has demonstrated characterization of melanin from basidiomycetes mushroom fungus, Schizophyllum commune and its applications.