Certain mushrooms like the death cap mushroom contain toxic compounds called amatoxins and phallotoxins that can cause liver and kidney failure in humans. The death cap is one of the most poisonous mushrooms in the world, with an ingestion of just one cap able to kill an adult. Its toxins work by inhibiting RNA polymerase in liver cells, preventing protein synthesis and ultimately causing cell death. Cases of death cap poisoning often involve mistaken identification, as it looks similar to edible mushrooms found in other countries. Proper identification requires examining spore features under a microscope or conducting chemical tests. While treatments for poisoning have improved, there is still no antidote and mortality depends on how quickly patients receive medical care after ingest

1. FUNGUSTOXINS
Mushroom
rouletteCan you tell the difference between a tasty paddy
straw mushroom and a toxic death cap? Emma
Shiells discovers the deadly chemistry hidden in
those gills
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2. www.chemistryworld.org | April 2013 | Chemistry World | 49
FUNGUSTOXINS
On a damp and drizzly autumnal morning
you may think there are better places to
be than foraging in the undergrowth of an
orchard, but amateur mushroom hunters are
sure to disagree with you. Martin Newcombe,
an ecologist and fungi enthusiast, is one of
those hooked.
‘The fact that fungi can grow so quickly
makes them fascinating,’ says Newcombe.
‘They typically grow in two to three days
depending on the environmental parameters.’
For some species, such as the stinkhorn, ‘they
can take just a matter of hours,’ he says. The
fungal kingdom consists of a wide range of
organisms that differ in their size, shape and
colour, and in their means of reproduction
and spore distribution. You could hold up
two mushrooms that appear identical to the
naked eye, but on closer inspection find that
they are two different species entirely – one
edible, the other poisonous. It is only when
you take a closer look at the spores using a
microscope that you can identify the species
accurately. ‘The spores are uniquely coloured,
patterned and sculpted for each species, while
some of them also undergo specific chemical
reactions as well,’ explains Newcombe. ‘In the
field, there is often a limit to what you can do
in terms of identification, as sometimes you
can only recognise the genus until further
tests can be carried out back in the lab. Only
once you’ve looked at the spores in more detail
and carried out some chemical tests, can you
truly identify the species and determine its
edibility,’ he adds.
No one really knows what mushroom
colours are for, as they are not necessarily
warnings. Contrary to popular belief, not
all poisonous toadstools are bright red with
white spots or warn you with lurid yellow and
green colours. Often poisonous mushrooms
look like the edible varieties you might buy
in a shop and therein lies the danger for the
inexperienced forager.
Deathbyname,deathbynature
‘Death cap is still the commonest cause of
[mushroom] poisoning in Europe,’ says
Newcombe. A notorious fungus, it is part of
the Amanita genus that contains around 600
species, some of which are the most highly
toxic in the world. It is believed that this
genus alone is responsible for approximately
95% of all mushroom poisonings, with 75%
of fatal fungal poisonings attributed to death
caps (Amanita phalloides) and the related
destroying angel (A. virosa).1
The toxicity of the Amanita species is due
to the presence of two groups of toxins called
amatoxins and phallotoxins, both multicyclic
peptides. It is believed that the death cap
contains six related phallotoxins and five or
more amatoxins.2
Geoffrey Kibby, a research
associate at the Royal Botanic Gardens at
Kew in the UK says that death cap ‘smells
like gone-off, sickly sweet honey and they
apparently taste really good. But you only
need one cap to kill an adult; they are pretty
nasty things to eat.’
After someone has eaten the deadly
mushrooms, ‘there’s usually a delay of
between six and 30 hours from ingestion
before the symptoms start to present
themselves,’ explains Kibby. ‘Typically the
person will experience food poisoning-type
symptoms: severe abdominal pain, sickness
and diarrhoea, briefly followed by a day or so
of apparent recovery,’ he says. ‘However, the
patient will then relapse and deteriorate quite
rapidly due to severe renal and liver failure’
often leading to death.
The less-harmful phallotoxins are
responsible for the initial gastrointestinal
symptoms, but it is the amatoxins that cause
the most damage internally. In particular,
α-amanitin has a high specificity for RNA
polymerase II in the liver. By inhibiting this
enzyme it prevents the formation of mRNA
and stops protein synthesis, resulting in cell
death and subsequent liver failure. When
filtered through the kidneys, the toxin can
then be reabsorbed into the bloodstream
and recirculated around the body, causing
repeated liver and kidney damage.3
The death rate has certainly decreased over
the years, thanks to advances in treatments,
according to Kibby. ‘In the US, they have more
cases than we do [in the UK], so they’ve had
more opportunity to try different treatments.
Standard treatments usually involve large
doses of penicillin and vitamin C, as well as
keeping the liver and kidneys going,’ he says.
Blood can be filtered using carbon-column
haemodialysis units or attempting organ
transplants in severe cases. A drug called
silibilin is currently in trials, according
to Kibby, and seems to be very effective.
Research shows that the drug works by
preventing the uptake of the amatoxins by the
liver cells and thereby protecting undamaged
liver tissue. It also stimulates DNA-dependent
RNA polymerases, resulting in an increase in
RNA synthesis.4
But treatment is not always successful and
it very much depends on how quickly people
are diagnosed after ingestion. Victims who
are hospitalised and given treatment almost
Mushroomsfromthe
Amanitagenus,suchas
deathcap(A.phalloides,
top) ordestroyingangel
(A.virosa,bottom),canbe
poisonous
Theamatoxin α-amanitin
hasahighspecificityfor
RNApolymeraseIIinthe
liverandcausesdeath
throughliverfailure
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fungustoxins
immediately after ingestion have a mortality
rate of around 10%, whereas those admitted
60 hours or more after ingestion have a
50–90% mortality rate.5
In spite of years of
detailed research into its toxins, death cap is
still the most deadly fungus known, and there
is still no known antidote for humans.
Mistakenidentity
Almost all poisoning cases that Kibby has been
involved in have been due to misidentification,
where immigrants have picked what they
thought they recognised from their native
country, or based on knowledge passed down
from older generations. Recently, Australian
news channels reported a case where four
people in Canberra accidently poisoned
themselves after consuming death cap at a New
Year’s Eve party. Two of them later died. They
were of Asian descent, and it is believed that they
may have mistaken the death caps for edible
paddy straw mushrooms (Volvariellavolvacea), a
common ingredient used in Asian cuisine.
Brett Summerell, a
fungi expert from the
Royal Botanic Gardens
in Sydney, Australia,
told ABC News shortly
after the deaths that
‘mushrooms that
are poisonous in Australia are very close
relatives to those that are quite safe to eat and
have a very similar appearance to the straw
mushroom’. Newcombe agrees: ‘They’ve come
from a culture where mushrooms like that are
eaten and so probably thought they recognised
them, rather than identified them.’
Since these deaths, the Australian
government and the Australian National
Botanical Gardens have released a factsheet
on death caps.6
It provides detailed
descriptions and photographs, as well as
possible locations in southern Australia and
what symptoms to expect. They emphasise
the importance of not confusing death caps
with the edible straw mushrooms that are
grown and eaten in Asia. Even though the
straw mushrooms are not native to Australia,
a related species V. speciosa is and looks very
similar to straw mushrooms. They have even
been found to grow side by side with the
death caps in some areas of Australia. Each
species in the Volvariella genus has a volva
at the base of the stem and gills that do not
reach the stem – just like the death cap. As the
guidebook3
says, ‘great care should be taken
in identification to avoid confusion with the
deadly white-spored Amanitas’.
‘The greenish form of death cap does
look like the paddy straw mushroom,’ says
Kibby. ‘Even the bulbous bag at the base of
the stem can be present on the paddy straw
mushroom so that wouldn’t have alerted
them initially.’ The only way to tell them
apart is by looking at their spores, according
to Kibby: ‘The paddy straw mushrooms have
pink spores whereas the death cap have
white spores.’ There are also chemical tests
that can be carried out: adding sulfuric acid
to the mushroom’s stem or gills will turn
black if it is a death cap. The Meixner test
uses concentrated hydrochloric acid and
newspaper to determine the presence of the
deadly toxin α-amanitin.7
‘Greatcareshould
betakenin
identificationto
avoidconfusion’
Paddystrawmushrooms
(V.volvacea,left)are
commonlyeateninAsian
cuisines.Althoughthey
donotgrowinAustralia,
therelated V.speciosa
(below,right)do–often
rightnexttothesimilar
lookingdeathcaps
(below,left)
As an experienced mycologist, Kibby is
often called upon to help with mushroom
poisonings via the National Poisons
Information Service (NPIS), which is a clinical
toxicology service available for healthcare
professionals in the UK. In 2011, the NPIS
saw 257 poisoning cases linked to eating
mushrooms in the UK, but without any deaths
in over four years. That was until last year,
when Kibby’s expertise was urgently needed
as a married couple were hospitalised after
eating mushrooms suspected to be death
caps. ‘[NPIS] got the son to go down to the
bottom of the garden and photograph the
mushrooms for me, they also packaged
some up and sent them to me in London that
same afternoon,’ explains Kibby. ‘As soon
as I opened the package I could smell that
gone-off honey smell that is so typical for
A. phalloides [death cap].’
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fungustoxins
Sadly the woman died from multiple organ
failure, but her husband survived having only
consumed a very small amount of the fungi.
‘She was doubly unlucky, as it was the end of
the year so they shouldn’t have been there in
the first place, and they were albino in colour;
the least typical colour form [for death caps],’
says Kibby. ‘Apparently, she had identified
them as edible mushrooms using a field guide,’
he adds.
Metalrecycling
Unfortunately, even non-poisonous fungi
can be pretty bad for you, because they
are very good at recycling. They are non-
photosynthetic organisms, gaining energy
and nutrients for their biosynthetic pathways
by degrading plants and other matter, which
means they can easily absorb trace elements
from their local environment.
Fungi collected near former smelters,
landfill sites and land treated with sewage
sludge can accumulate significant quantities of
metal ions, such as cadmium, mercury, lead,
copper and chromium. Even worse, high levels
of radioactive caesium-137 have been found in
mushrooms. ‘It was only a few years ago that
the British government stopped monitoring
toadstools generally from the fallout at
Chernobyl,’ says Newcombe. Kibby believes
that there are still some areas of far eastern
Scandinavia where picking mushrooms is
not advisable, due to the radioactive nuclides
found in them.
Newcombe once harvested mushrooms
growing near a disused factory that was an
old iron smelter. ‘You could taste the iron
in them,’ he says. ‘I sent samples off to be
tested and, sure enough, there was more iron
in them than there
should have been.’ And
mushrooms that grow
near roadside edges
can absorb metals
from passing vehicles.
The mushrooms
themselves might
be edible, but once
they have absorbed
metals from their surrounding environment
they can become poisonous due to the
high concentration of heavy metals found
inside them.
Readerbeware
In the UK, collecting mushrooms is more of an
occasional pastime, whereas in other cultures
people pick them for everyday consumption.
In mainland Europe, pharmacists can be
asked to help identify them. ‘Problems arise
when people try to identify edible mushrooms
using only a guidebook. If you want to eat wild
‘Problemsarise
whenpeopletry
toidentifyedible
mushrooms
usingonlya
guidebook’
Boletusedulisareedible
andhardtomistakefor
poisonousvarieties
HailCaesar!
NotallmushroomsfromtheAmanitagenusare
badforyourhealth;someofitsspeciesareedible,
likethegloriousAmanitacaesareawithitsorange
capandyellowstemandgills.KnowninEnglishas
Caesar’smushroom,ithasbeenprizedsinceRoman
timesandisnoteasilyconfusedwithotherAmanita
species,thankstoitsvibrantcolouring.Ithasyetto
befoundintheUK,butgrowsinwarmerclimates
likesouthernEuropeandNorthAfrica.Itwassaid
tobeafavouriteoftheRomanemperorClaudius
andhasbeenfoundgrowingalongoldRoman
roads.ManyancienthistoriansbelievethatClaudius
diedfrommushroompoisoning,murderedbyhis
ownwifeAgrippinainAD54.Ithasbeenwidely
speculatedthatdeathcapswereusedasthepoison,
butitisnowconsideredtobeunlikelygiventhe
shorttimeframereportedbetweenhimgettingsick
anddying.8
KibbyhastriedsomeedibleAmanitas,‘buteven
thenmyheartwasinmymouth,’headds.Hehas
eatenA.rubescens,whichalthoughedibleafter
cooking,arepoisonousifeatenraw.‘Itdidtaste
deliciousalthoughIcouldn’thelpbutwatchfor
symptomsoverthenextfewhours,’hesays.
PrizedbytheRomans,thebrightlycolouredA.caesareaisoneoftheedibleAmanitavarieties
mushrooms, you’ve got to go on organised
forays with someone that knows what they are
doing,’ says Kibby. ‘No matter how good the
field guide is, it can’t possibly cover all colour
variations and eventualities. It seems silly to
risk your life when you can go to your local deli
and buy exotic mushrooms there,’ he says.
Kibby says that, contrary to what you might
expect, most poisonings happen not from
picking really weird-looking mushroom, but
from the most normal looking ones, such
as paddy straw mushrooms. ‘If only people
would stick to really weird and wonderful
mushrooms like some Boletus,’ he says. ‘Then
you can’t go wrong as you can’t mistake them
for anything else.’
References
1 J R Hanson, The chemistry of fungi, RSC Publishing,
Cambridge, 2008
2 G Kibby, Guide to mushrooms of Britain and Europe,
Octopus Publishing, 2006
3 R Phillip, Mushrooms and other fungi of Great Britain and
Europe, Pan, London, 1981
4 K Hruby, G Csomos, M Fuhrmann and H Thaler, Hum.
Toxicol., 1983, 2, 183 (DOI: 10.1177/
096032718300200203)
5 The Bad Bug Book, US Food and Drug Administration,
2nd ed, 2012, p200 http://1.usa.gov/XO6DF6
6 Australian National Botanical Gardens
http://bit.ly/10gSeRl
7 M Beuhler, DC Lee and R Gerkin, Ann. Emerg. Med., 2004,
44, 114 (DOI: 10.1016/j.annemergmed.2004.03.017)
8 V J Marmion and T E J Wiedemann, J. R. Soc. Med., 2002,
95, 260 (DOI: 10.1258/jrsm.95.5.260)
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