DNA
Barcoding for the Identification of Medicinal and Culinary Mushrooms
Reviewed: Raja HA, Baker TR, Little
JG, Oberlies NH. DNA
barcoding for identification of consumer-relevant mushrooms: A partial solution
for product certification? Food Chem.
2017;214:383-392.
Keywords: DNA barcoding, mushrooms,
authentication, Ganoderma lucidum, Ophiocordyceps sinensis
Attributing the correct scientific name to
dietary ingredients made from fungal materials remains a challenge, in part due
to difficulties in species authentication by chemical means and the nature of
fungal taxonomic names, which are undergoing numerous taxonomic revisions with
the application of molecular methods. This study evaluated the utility of the
ITS region (which is the barcode accepted by the Consortium for the Barcode of
Life for fungi) towards DNA-based identification of mushrooms sold for
medicinal and/or culinary purposes. The main goal of the study, which was
performed as a collaboration of academic researchers (University of North
Carolina at Greensboro) and industry scientists (Procter & Gamble and New
Chapter, Inc.), was to demonstrate that Sanger sequencing of the ITS region is
an appropriate means for verification of species identities.
A total of 33 samples (20 powdered mycelium
samples from a commercial supplier; six grocery store mushrooms; and seven
dietary supplements containing powdered fungal materials) were included in the
study. The results indicated that 10 samples (30%) displayed accurate
binomials. Another 10 samples listed the genus name accurately, but had
improper species names. As an example, five of the six products labeled to
contain reishi (Ganoderma lucidum,
Ganodermataceae) contained either G. sichuanense
or G. resinaceum. In five (15%) of all
samples, the genus or species indicated on the label was incorrect. This
included four of the six samples sold as Cordyceps sinensis
(current name Ophiocordyceps sinensis, Ophiocordycipitaceae),
where three products were found to contain Tolypocladium inflatum*
(Ophiocordycipitaceae) and one, Inonotus sanghuang
(Hymenochaetaceae).
From the remaining 24% of samples, including
two products listed to contain cordyceps and one listed as reishi, the authors
were not able to obtain DNA for ITS sequencing, as these samples were processed
to the extent that no suitable DNA could be extracted. The grocery store
mushroom barcoding results showed that three samples (50%) were correctly
labeled, while in one sample, the exact species could not be obtained (the
fungal genus was accurately labeled). In another case, no suitable DNA was
obtained to determine species identity. Interestingly, the last sample labeled
to contain porcini (Boletus edulis,
Boletaceae) was identified as B. shiyong, which
is the first record of this mushroom in the United States.
The authors listed four important points for
consideration when using DNA barcoding to identify mushrooms: (1) DNA barcoding
via Sanger sequencing of the ITS region should be used only on materials that
have been minimally processed; (2) DNA barcoding cannot be performed via Sanger
sequencing on samples containing mixed species; (3) DNA barcoding works
efficiently and accurately if accurate reference sequence databases are
available; and (4) DNA barcoding can provide only a partial solution for
product certification, and other, orthogonal techniques, such as those provided
by analytical chemistry, may also serve to ensure the lack of contamination and
adulteration of these substances.
The researchers hope that their study will encourage
International Sequence Databases, such as GenBank, to work on the RefSeq
database. This database consists of fully annotated ITS
sequences obtained by expert mycologists for medicinally important as well as commercially
sold mushrooms and is maintained by the National Center for Biotechnology
Information (NBCI).
Comment: Dietary supplements containing
mycelium (the branched, thread-like vegetative growth of mushrooms) or fruiting
bodies of fungi have gained in popularity and are expected to continue gaining
importance in the marketplace.2,3 Even in the presence of the
fruiting bodies, correct identification requires considerable expertise.
Authentication becomes more complicated when powdered materials or fungal
extracts are used. Chemical fingerprints have been used successfully for the
identification of a number of fungi, but the composition is often dominated by
similar polysaccharides and terpenoids, making chemical authentication
challenging.4 Genetic methods, such as DNA barcoding, offer an
alternative way to establish the identity of medicinal mushrooms, and unlike
with medicinal plants, experts have been able to agree on ITS as a suitable
genetic region for DNA barcoding. However, as evidenced by the data from Raja
et al., the same limitations observed with DNA barcoding for plants are also
seen with fungi. As such, the method should be used only for crude raw material
and in combination with orthogonal methods, e.g., botanical, macroscopic,
microscopic, and/or chemical analysis.
*Note: Spores
from Cordyceps subsessilis (syn. Elaphocordyceps subsessilis,
Ophiocordycipitaceae) are known to produce colonies of Tolypocladium inflatum, which is a phenomenon known as
anamorphism. Quandt et al. suggest that the three names, C.
subsessilis, E. subsessilis,
and T. inflatum, should be considered as
synonyms.1 Tolypocladium inflatum
is of medicinal interest since it is the source of the immunosuppressant
ciclosporin.
References
1. Quandt CA, Kepler RM, Gams W, et al. Phylogenetic-based nomenclatural
proposals for Ophiocordycipitaceae (Hypocreales) with new combinations in Tolypocladium. IMA Fungus.
2014;5(1):121-134.
2. Daniells S. Five key Expo West supplement trends. NutraIngredients-USA
website. Available at: http://www.nutraingredients-usa.com/Markets/Five-key-Expo-West-supplement-trends. Published March 16, 2016. Updated March 22, 2016. Accessed December 13,
2016.
3. Smith T, Kawa K, Eckl V, Johnson J. Sales of herbal dietary supplements
in US increased 7.5% in 2015. HerbalGram.
2016;(111):67-73. Available at: http://cms.herbalgram.org/herbalgram/issue111/hg111-mktrpt.html. Accessed December 13, 2016.
4. Elsayed EA, El Enshasy H, Wadaan MAM, Aziz R. Mushrooms: a potential natural source of anti-inflammatory compounds for medical
applications. Mediators Inflamm.
2014;2014:805841. doi: 10.1155/2014/805841.
