Authentication of Iceland Moss (Cetraria islandica) by UPLC-QToF-MS chemical profiling and DNA barcoding

The lichen Cetraria islandica or Iceland Moss is commonly consumed as tea, food ingredients (e.g. in soup or bread) and herbal medicines. C. islandica, which has two chemotypes, can be difficult to distinguish from the sister species Cetraria ericetorum. They are collectively referred to as the Cetraria islandica species complex. This study aimed to use an UPLC-QToF-MS chemical profiling together with DNA barcoding to distinguish species and chemotypes of the C. islandica species complex. Our results show that the two chemotypes of C. islandica are clearly distinguishable from each other and from C. ericetorum by the chemometric approach. The RPB2 barcode was able to differentiate C. islandica from C. ericetorum with a barcode gap, but the widely used nrITS barcode failed. Neither of them could discriminate chemotypes of C. islandica. In conclusion, this integrative approach involving chemical profiling and DNA barcoding could be applied for authentication of Iceland Moss materials

Major lichen metabolites (1–7) and unknown minor compounds (a-c) in Icelandic <i>Melanelia</i> taxa.

<p>Major lichen metabolites (1–7) and unknown minor compounds (a-c) in Icelandic <i>Melanelia</i> taxa.</p

Genetic distances, alignment length and number of specimens (haplotypes) for the genera <i>Melanelia</i> and <i>Montanelia</i>.

<p>Genetic distances, alignment length and number of specimens (haplotypes) for the genera <i>Melanelia</i> and <i>Montanelia</i>.</p

Fungal nrITS gene tree obtained from 116 <i>Melanelia</i> and <i>Montanelia</i> specimens.

<p>(A) Neighbor-joining tree, bootstrap values over 80% are labelled on the branches; (B) Maximum-likelihood tree, posterior probability/bootstrap values are labelled on branches.</p

Chemical structures of major compounds in Icelandic <i>Melanelia</i> lichens.

<p>Compounds include cryptostictic acid <b>1</b>, stictic acid <b>2</b>, norstictic acid <b>3</b>, usnic acid <b>4</b>, stenosporic acid <b>5</b>, rangiformic acid <b>6</b> and perlatolic acid <b>7</b>.</p

Multivariate analysis of LC-MS metabolite data.

<p>(A) PCA plot of chemical profiles of Icelandic <i>Melanelia</i> lichens, where <i>M</i>. <i>agnata</i> and <i>M</i>. <i>stygia</i> are clustered. (B) OPLS-DA plot shows the separation of the two <i>Melanelia</i> taxa. The metabolome of <i>M</i>. <i>agnata</i> and <i>M</i>. <i>stygia</i> can be differentiated with a high level of prediction value: R²Y(cum) = 1, Q²(com) = 0.99. (C) Loading S-plot from LC-MS data of <i>M</i>. <i>agnata</i> and <i>M</i>. <i>stygia</i>. Cut-off values of p(corr) < |0.8| were selected to designate the metabolites contribuiting significantly to the overall difference (area in color) between <i>M</i>. <i>agnata</i> and <i>M</i>. <i>stygia</i>. Two metabolites were thus identified from each species.</p

MS fragmentation patterns of depsidones in the lichen <i>Melanelia hepatizon</i>.

<p>Compounds include cryptostictic acid <b>1</b>, stictic acid <b>2</b> and norstictic acid <b>3</b>.</p

Genetic distance histograms and barcoding gap analysis for reported <i>Melanelia</i> species in Iceland.

<p>(A and B) p-Distance histogram for the genus <i>Melanelia</i> and <i>Montanelia</i>, respectively; (C and D) Barcoding gap analysis for <i>Melanelia</i> species and <i>Montanelia disjuncta</i>.</p

MS fragmentation pathway of usnic acid.

<p>Usnic acid was detected in one chemotype of Icelandic <i>Montanelia disjuncta</i> taxon. Structure a, b, d, e and f are characteristic fragment ions in MS² spectrum (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178012#pone.0178012.s004" target="_blank">S3 Fig</a>). Structure b is a resonance contributor of structure a but not a true structure of usnic acid. Structure c is only reported in LDI or FAB-MS. (Abbreviation: RDA: retro-Diels—Alder reaction; LDI/FAB: laser desorption ionization/fast atom bombardment).</p