Secondary metabolism in the lichen symbiosis

Diversity and specificity of molecular functions in cyanobacterial symbionts

Cyanobacteria are globally occurring photosynthetic bacteria notable for their contribution to primary production and production of toxins which have detrimental ecosystem impacts. Furthermore, cyanobacteria can form mutualistic symbiotic relationships with a diverse set of eukaryotes, including land plants, aquatic plankton and fungi. Nevertheless, not all cyanobacteria are found in symbiotic associations suggesting symbiotic cyanobacteria have evolved specializations that facilitate host-interactions. Photosynthetic capabilities, nitrogen fixation, and the production of complex biochemicals are key functions provided by host-associated cyanobacterial symbionts. To explore if additional specializations are associated with such lifestyles in cyanobacteria, we have conducted comparative phylogenomics of molecular functions and of biosynthetic gene clusters (BGCs) in 984 cyanobacterial genomes. Cyanobacteria with host-associated and symbiotic lifestyles were concentrated in the family Nostocaceae, where eight monophyletic clades correspond to specific host taxa. In agreement with previous studies, symbionts are likely to provide fixed nitrogen to their eukaryotic partners, through multiple different nitrogen fixation pathways. Additionally, our analyses identified chitin metabolising pathways in cyanobacteria associated with specific host groups, while obligate symbionts had fewer BGCs. The conservation of molecular functions and BGCs between closely related symbiotic and free-living cyanobacteria suggests the potential for additional cyanobacteria to form symbiotic relationships than is currently known.

Antibacterial mechanism of the methanol extract of Thamnolia subuliformis (Ehrh.) W. Culb against Staphylococcus aureus

Thamnolia subuliformis (Ehrh.) W. Culb is a species of lichen with edible and medicinal applications in China. Our previous studies demonstrated that the methanol extract of Thamnolia subuliformis (METS) exhibits broad antibacterial activity and stability against foodborne pathogens. This study aimed to investigate the antibacterial mechanism of METS against Staphylococcus aureus using nontargeted metabolomics, focusing on cell wall and membrane damage. The results revealed that the minimum inhibitory concentration (MIC) was 0.625 mg ml-1 and that METS had good biosafety at this concentration. METS caused significant damage to the cell wall and membrane integrity, based on both morphological observation by electron microscopy and the leakage of alkaline phosphatase, protein, and nucleic acid in the cell cultures. Treatment with METS at the MIC disrupted the lipid metabolism of S. aureus, causing a decrease in the metabolism of various phospholipids and sphingolipids in the cell membrane and an increase in the ratio of saturated fatty acids to unsaturated fatty acids. Moreover, it influenced intracellular amino acid and energy metabolism. These results shed light on the antibacterial mechanism of METS against S. aureus while also serving as a reference for the further development of natural antibacterial compounds derived from Thamnolia subuliformis.

Isolation and Identification of Lichen Photobionts Collected from Different Environments in North of Portugal and Evaluation of Bioactivities of Their Extracts

Lichens are organisms constituted by a symbiotic relationship between a fungus (mycobiont) and a photoautotrophic partner (photobiont). Lichens produce several bioactive compounds; however, the biotechnological exploitation of this organism is hampered by its slow growth. To start studying the possibility of exploiting lichens as alternative sources of bioactive compounds, eighteen lichens were collected in the north of Portugal in order to isolate and study the bioactivity of their photobionts. It was possible to isolate and cultivate only eight photobionts. Three of them, LFR1, LFA2 and LCF3, belong to the Coelastrella genus, the other two (LFA1 and LCF1) belong to the Chlorella genus and for the remaining three photobionts, LFS1, LCA1 and LCR1, it was impossible to isolate their microalgae. These only grow in consortium with bacteria and/or cyanobacteria. All extracts showed antioxidant activity, mainly at a concentration of 10 mg.mL-1. LFS1, a consortium extract, showed the highest antioxidant power, as well as the highest concentration of phenolic compounds (5.16 ± 0.53 mg of gallic acid equivalents (GAE).g-1). The extracts under study did not show significant antibacterial activity against Escherichia coli, Listeria or Salmonella. The Coelastrella sp. and LFA1 extracts showed the highest hyaluronidase inhibition. The LFR1 extract at a concentration of 5 mg.mL-1 showed the highest anti-inflammatory activity (79.77 ± 7.66%). The extracts of Coelastrella sp. and LFA1 also showed greater antidiabetic activity, demonstrating the high inhibitory power of α-amylase and α-glucosidase. LFR1 at a concentration of 5 mg.mL-1, due to its selective cytotoxicity inhibiting the growth of cancer cells (Caco-2 cells), is a promising anticancer agent.

First report of betalain production from endolichenic Bacillus sp. LDAB-1 from Dirinaria aegilita: Insights from novel quantification methodology of image processing

Pigments are widely used in food supplements envisaging attractive colors along with health benefits. The desired advancements in the nutraceutical and antioxidant properties of pigments utilized in food products necessitate the search for novel additives. The present study is the first in the field to report the pigment-producing endolichenic bacteria, Bacillus sp. LDAB-1 from Dirinaria aegilita. Morphological, biochemical, and molecular characterization of the bacterium emphasizes that ideal pigment production occurs when utilizing sucrose and sodium nitrate. The pigment was salted out and dialyzed for further qualitative characterization using ultraviolet-visible, fluorescence, and Fourier transform infrared spectra and the results corroborated the presence of betalains. The antioxidant activity of betalain is closer to the efficiency of α-tocopherol, which confers the pigment properties for antioxidant and nutraceutical significance. An optimal methodology for pigment affirmation is an issue when using an alternative methodology. Hence, the present assessment employs a comparative analysis of findings from both a spectrophotometric method and image processing technology encompassing RGB, CMYK, YCbCr, and L*a*b* color space models. Amongst these, the L*a*b* model potentially provides an effective modality for determining the pigment concentration. Bland-Altman plot analysis indicates similar consistency levels in betalain quantification by both methods at 95% confidence intervals, affirming the integrity and consistency of color image processing technology. Consequently, the present study represents novelty and innovativeness in reporting endolichenic Bacillus sp. LDAB-1 from D. aegilita and a rational image optimization protocol for pigment elucidation characteristics.

A New Rare Halogenated Depside from Lichen and Study of its Anti-Proliferative Activity

Lichens are a symbiotic association of algae and fungus, belonging to the family Parmeliaceae. Some lichen species are edible and used as an active ingredient for preparation of exotic spices as well as folklore medicine to cure different kinds of ailments. A specimen of lichen was collected from Munner in the Kerala State of South India for chemical profiling. Chemical analyses of the diethyl ether extract of the defatted lichen led to the isolation of six phenols 1-6 with variation of relative abundance. Amongst them, the relative abundance of compound 3 was the greatest (1 % of crude extract) and it was identified as atranorin. The structures of known compounds were confirmed by comparison of their 1H-NMR, 13C NMR, and mass data with published values available in the literature. In vitro bioassay for anti-proliferative activity of these compounds has been conducted against various human cancer cell lines in comparison with paclitaxel as control using SRB assay. Interestingly, a new compound 5 was found along with previously reported compounds from this lichen. This new compound was designated as fluoroatranorin 5 which was reported for the first time herein. The structural characterization of a new depside was determined by spectral methods such as 1H-NMR, 13C NMR, 19F NMR, IR, LC-HRESI-MS, and LC-MS/MS study. Its structure was confirmed by single crystal X-ray diffraction study. This new compound was designated as fluoroatranorin 5 which was reported first time herein. Anti-proliferative activity of all these compounds was evaluated against six different cancer cell lines. The inhibitory activity, IC50 value of compounds 1-3 and 5 exhibited at 99.64, 102.04, 109.20, 53.0 and 2.4 μM on cancer cell lines HT-29 (colon), Hela (cervical), HT-29, HPAC (pancreas) and A2780 (ovarian cancer cell line) respectively in comparison with paclitaxel as control. The new compound 5 exhibited significant activity with IC50 value 2.4 μM on A2780 ovarian cancer cell line.

Neutralizing activity of Usnic acid and β-cyclodextrins complex against SARS-CoV-2 spike pseudovirus

The rapid spread of SARS-CoV-2 and its infection severity require an urgent development of antiviral agents. In this respect, Usnic acid (UA), a natural dibenzofuran derivative, exerts antiviral activity against several viruses, though presenting very low solubility and high cytotoxicity. Here, UA was complexed with β-cyclodextrins (β-CDs), a pharmaceutical excipient used to improve drug solubility. The cytotoxic activity, tested on Vero E6 cells, revealed no effect for β-CDs alone whereas significant cytotoxicity for the UA/β-CDs complex was recorded at concentrations ≥ 0.05%. The neutralizing activity towards the fusion of SARS-CoV-2 Spike Pseudovirus showed no effects for β-CDs alone whereas the UA/β-CDs complex, when pre-incubated with the viral particles, efficiently inhibited the Pseudoviral fusion of about 90 and 82% at non-cytotoxic concentrations of 0.03 and 0.01%, respectively. In conclusion, although further evidences are needed to clarify the exact inhibition mechanism, UA/β-CDs complex could be useful in SARS-CoV-2 infection.

Chemical composition and antioxidant, enzyme inhibition and cytoprotective activity of two Antarctic lichens of the genus Psoroma (Pannariaceae)

Lichens contain different types of chemical compounds with multiple biological activities that demonstrate their potential pharmacological use. This research aims to report the metabolomic identification of the ethanolic extracts of P. antarcticum and P. hypnorum, their antioxidant, enzyme inhibitory, and their cytoprotection activity. Sixteen metabolites were identified in P. antarcticum and twelve in P. hypnorum; the extracts reported variable antioxidant activity with IC50 >350 µg/mL in DPPH·, values >18 µmol Trolox/g in ORAC and >40 µmol Trolox/g in FRAP and a phenolic compound content >10 mg GAE/g, as well as significant results in cholinesterases, α-glucosidase, pancreatic lipase, α-amylase, and tyrosinase enzyme inhibition activities with IC50 ranging from 18 to 510 µg/mL, and which were complemented by molecular docking experiments. Both extracts showed improved cytoprotection at the concentrations of 0.5 to 1.0 μg/mL. This study contributes to the knowledge of the chemical diversity of Antarctic lichen extracts and their effectiveness in the evaluation of biological activities related to neurodegenerative diseases and metabolic syndrome.

CASE-DFT Structure Elucidation of Proton-Deficient Chlorodepsidones from the Indonesian Lichen Teloschistes flavicans and Structure Revision of Flavicansone

Biodiscovery efforts in Indonesia have aimed to explore the understudied chemical diversity of its rich lichen flora, seeking to find new products endowed with significant biological properties. The chemical screening of a Teloschistes flavicans extract led to selection of this species for further investigation. LC/MS and 1H NMR-based dereplication pinpointed six chlorodepsidones from the thallus of a sample of this lichen. This led to the streamlined isolation and the subsequent structure elucidation of the three new compounds norflavicansone 1, flavicansone 2, and isocaloploicin 3, along with the known chlorodepsidones 4-6, stictic acid 7, aurantiamide acetate 8, and parietin 9. The challenging structure elucidation of these proton-deficient metabolites benefited from a state-of-the-art workflow involving a synergistic combination of Computer-Assisted Structure Elucidation (CASE) and Density Functional Theory (DFT) calculations of the top-ranked candidates. This investigation also led to the revision of flavicansone's structure, previously described from this species. The three new molecules that are being reported here are remarkable in that they represent hybrid depsidones in which one of the aromatic rings is derived from orsellinic acid and the other is derived from β-orcinol, a rare structural feature for lichen depsidones.

Liquid chromatography-electrospray ionization-mass spectrometry/mass spectrometry characterization of depsides and depsidones from the Chilean lichen Parmotrema perlatum

Lichens are recognized by their unique compounds and diverse applications in food, medicines, and cosmetics. Using ultra-high pressure liquid chromatography, coupled with a high-resolution mass spectrometer, metabolomic profiling of the lichen Parmotrema perlatum, from a methanolic extract, was performed. Based on characteristic fragmentation patterns, twenty-five lichenic substances were tentatively identified including 5 depsides, 12 depsidones, 2 diphenyl ethers, 1 aromatic considered as possible artifact, 1 dibenzofuran, 1 carbohydrate, 1 organic acid, and 2 undefined compounds. To the best of our knowledge, this is a more complete report of their phytochemistry from P perlatum. Our findings of the P perlatum profile may contribute and complement the current data of the Parmotrema genus.

Δ-Keto-acid/hydroxy-lactone isomerization in some lichen depsides, depsidones and diphenyl ethers

In some compounds in lichens, the carboxylic acid is ortho-substituted by an 2-oxoalkyl chain. This particular structure induces the existence of δ-keto-acid ka or hydroxy-lactone hl isomers, clearly identified by their NMR data and chemical properties, such as dehydration, methylation and behaviour in thermal conditions. Internal hydrogen bonding between the carboxylic acid and substituent in the ortho' position is proposed as an isomerization modulator: an H-bond acceptor (OCH3) leads to ka isomers, whereas hl isomers are obtained with an H-bond donor (OH).

The Depside Derivative Pericodepside Inhibits Cancer Cell Metastasis and Proliferation by Suppressing Epithelial-Mesenchymal Transition

A depside derivative, named pericodepside (2), along with the known depside proatranorin III (1), was isolated from the solid cultivation of an Ascochyta rabiei strain that heterologously expresses atr1 and atr2 that are involved in the biosynthesis of atranorin in a fruticose lichen, Stereocaulon alpinum. The structure of 2 was determined by 1D and 2D NMR and MS spectroscopic data. The structure of 2 consisted of a depside-pericosine conjugate, with the depside moiety being identical to that found in 1, suggesting that 1 acted as an intermediate during the formation of 2 through the esterification process. Pericodepside (2) strongly suppressed cell invasion and proliferation by inhibiting epithelial-mesenchymal transition and the transcriptional activities of β-catenin, STAT, and NF-κB in U87 (glioma cancer), MCF-7 (breast cancer), and PC3 (prostate cancer) cell lines.

An Antarctic lichen isolate (Cladonia borealis) genome reveals potential adaptation to extreme environments

Cladonia borealis is a lichen that inhabits Antarctica's harsh environment. We sequenced the whole genome of a C. borealis culture isolated from a specimen collected in Antarctica using long-read sequencing technology to identify specific genetic elements related to its potential environmental adaptation. The final genome assembly produced 48 scaffolds, the longest being 2.2 Mbp, a 1.6 Mbp N50 contig length, and a 36 Mbp total length. A total of 10,749 protein-coding genes were annotated, containing 33 biosynthetic gene clusters and 102 carbohydrate-active enzymes. A comparative genomics analysis was conducted on six Cladonia species, and the genome of C. borealis exhibited 45 expanded and 50 contracted gene families. We identified that C. borealis has more Copia transposable elements and expanded transporters (ABC transporters and magnesium transporters) compared to other Cladonia species. Our results suggest that these differences contribute to C. borealis' remarkable adaptability in the Antarctic environment. This study also provides a useful resource for the genomic analysis of lichens and genetic insights into the survival of species isolated from Antarctica.

Nutritional and Health-Promoting Effects of Lichens Used in Food Applications

PURPOSE OF REVIEW

Lichens have a huge significance which is used in nutrition due to the bioactive components within. Lichen is a nutrient-dense resourceful diet nearly every day meal and has long been used as food; also, these valuable natural resources are now being utilized for a wide range of other purposes. The purpose of this review was to evaluate the nutritional and edible qualities of lichens as well as the possible health benefits of lichens. It is interesting to note that lichen is a nutrient-dense and functional food. It is a nutritional resource that can mitigate the effects of malnutrition to some amount.

RECENT FINDINGS

There is an indication that an intake of lichens as natural foods was associated with nutritional and health-promoting properties. Lichens have proven to have theoretically rich nutritional value, and their extracts and active constituents have also been shown to have multiple health benefits. Low-fat content, high carbohydrate, and crude fibre content; plentiful mineral components; and good protein sources are all thought to contribute to lichen's nutritional value. There is a lot of potential for using lichens as an effective food source and ensuring people's food production.

Update on the state of research to manage Fusarium head blight

Fusarium head blight (FHB) is one of the most devastating diseases of cereal crops, causing severe reduction in yield and quality of grain worldwide. In the United States, the major causal agent of FHB is the mycotoxigenic fungus, Fusarium graminearum. The contamination of grain with mycotoxins, including deoxynivalenol and zearalenone, is a particularly serious concern due to its impact on the health of humans and livestock. For the past few decades, multidisciplinary studies have been conducted on management strategies designed to reduce the losses caused by FHB. However, effective management is still challenging due to the emergence of fungicide-tolerant strains of F. graminearum and the lack of highly resistant wheat and barley cultivars. This review presents multidisciplinary approaches that incorporate advances in genomics, genetic-engineering, new fungicide chemistries, applied biocontrol, and consideration of the disease cycle for management of FHB.

In Vitro and in Silico Studies of Lichen Compounds Atranorin and Salazinic Acid as Potential Antioxidant, Antibacterial and Anticancer Agents

Lichens are symbiotic organisms made up of alga/cyanobacterium and fungus. We investigated antioxidant, antibacterial and anticancer properties of two lichen compounds, atranorin and salazinic acid, and five lichen species: Heterodermia boryi, Heterodermia diademata, Heterodermia hypocaesia, Parmotrema reticulatum, and Stereocaulon foliolosum. Free radical scavenging, Ferric reducing potential, Nitric oxide scavenging, and Trolox equivalent capacity were used to measure antioxidant activity. Strong radical scavenging action was demonstrated by atranorin and salazinic acid, with IC50 values of 39.31 μM and 12.14 μM, respectively. The Minimum Inhibitory Concentration (MIC) assay based on resazurin, was used to measure antibacterial activity. Parmotrema reticulatum demonstrated significant antibacterial activity against Raoultella planticola with MIC of 7.8 μg/mL. Cytotoxicity assay on breast cancer cell line was used to assess anticancer activity. To further understand the binding locations on the target proteins Er (Estrogen Receptor alpha), EGFR (Epidermal Growth Factor Receptor), mTOR (Mammalian Target of Rapamycin), and PgR (Progesterone Receptor), molecular docking experiments were conducted. Docking study showed that the binding energies of atranorin and salazinic acid with mTOR were -5.31 kcal/mol and -3.43 kcal/mol, respectively. The results suggest that atranorin has the potential to be a multitargeted molecule with natural antioxidant, antibacterial, and anticancer properties.

Highlights of biosynthetic enzymes and natural products from symbiotic cyanobacteria

Covering: up to 2023Cyanobacteria have long been known for their intriguing repertoire of natural product scaffolds, which are often distinct from other phyla. Cyanobacteria are ecologically significant organisms that form a myriad of different symbioses including with sponges and ascidians in the marine environment or with plants and fungi, in the form of lichens, in terrestrial environments. Whilst there have been several high-profile discoveries of symbiotic cyanobacterial natural products, genomic data is scarce and discovery efforts have remained limited. However, the rise of (meta-)genomic sequencing has improved these efforts, emphasized by a steep increase in publications in recent years. This highlight focuses on selected examples of symbiotic cyanobacterial-derived natural products and their biosyntheses to link chemistry with corresponding biosynthetic logic. Further highlighted are remaining gaps in knowledge for the formation of characteristic structural motifs. It is anticipated that the continued rise of (meta-)genomic next-generation sequencing of symbiontic cyanobacterial systems will lead to many exciting discoveries in the future.

Persephacin Is a Broad-Spectrum Antifungal Aureobasidin Metabolite That Overcomes Intrinsic Resistance in Aspergillus fumigatus

Fungi pose a persistent threat to humankind with worrying indications that emerging and re-emerging pathogens (e.g., Candida auris, Coccidioides spp., drug-resistant Aspergilli, and more) exhibit resistance to the limited number of approved antifungals. To address this problem, our team is exploring endophytic fungi as a resource for the discovery of new antifungal natural products. The rationale behind this decision is based on evidence that endophytes engage with plants in mutualistic relationships wherein some fungi actively participate by producing chemical defense measures that suppress pathogenic microorganisms. To improve the odds of bioactive metabolite discovery, we developed a new hands-free laser-cutting system capable of generating >50 plant samples per minute that, in turn, enabled our team to prepare and screen large numbers of endophytic fungi. One of the fungal isolates obtained in this way was identified as an Elsinoë sp. that produced a unique aureobasidin analogue, persephacin (1). Some distinctive features of 1 are the absence of both phenylalanine residues combined with the incorporation of a novel amino acid residue, persephanine (9). Compound 1 exhibits potent antifungal effects against a large number of pathogenic yeast (including several clinical C. auris strains), as well as phylogenetically diverse filamentous fungi (e.g., Aspergillus fumigatus). In an ex vivo eye infection model, compound 1 outperformed standard-of-care treatments demonstrating the ability to suppress fluconazole-resistant Candida albicans and A. fumigatus at a concentration (0.1% solution) well below the clinically recommended levels used for fluconazole and natamycin (2% and 5% solutions, respectively). In 3D tissue models for acute dermal and ocular safety, 1 was found to be nontoxic and nonirritating at concentrations required to elicit antifungal activity. Natural product 1 appears to be a promising candidate for further investigation as a broad-spectrum antifungal capable of controlling a range of pathogens that negatively impact human, animal, and plant health.

Genome Mining and Biosynthetic Reconstitution of Fungal Depsidone Mollicellins Reveal a Dual Functional Cytochrome P450 for Ether Formation

Depsidones are significant in structural diversity and broad in biological activities; however, their biosynthetic pathways have not been well understood and have attracted considerable attention. Herein, we heterologously reconstituted a depsidone encoding gene cluster from Ovatospora sp. SCSIO SY280D in Aspergillus nidulans A1145, leading to production of mollicellins, a representative family of depsidones, and discovering a bifunctional P450 monooxygenase that catalyzes both ether formation and hydroxylation in the biosynthesis of the mollicellins. The functions of a decarboxylase and an aromatic prenyltransferase are also characterized to understand the tailoring modification steps. This work provides important insights into the biosynthesis of mollicellins.

Discovery of Naphthol Tetramers from Endolichenic Fungus Daldinia childiae 047219 Based on MS/MS Molecular Networking

Feature-based molecular networking analysis suggested the presence of naphthol tetramers in Daldinia childae 047219, the same species but a different strain from one used previously for the discovery of naphthol trimers promoting adiponectin synthesis. The new tetramers were composed of 5-methoxy-4-naphthol, each of which was connected to one another in various positions. Targeted isolation afforded six previously unreported naphthol tetramers (1-6) together with 13 known polyketides (7-19) including naphthol monomers, dimers, and trimers. Structures of the isolated compounds were established by using NMR and mass spectroscopic analysis. Nodulisporin A (13), nodulisporin B (14), and 1,1',3',3″-ternaphthalene-5,5',5″-trimethoxy-4,4',4″-triol (16) demonstrated anti-inflammatory activities against NO production, but the new compounds were less active.

Identification of a biosynthetic gene cluster for a red pigment cristazarin produced by a lichen-forming fungus Cladonia metacorallifera

Lichens are known to produce many novel bioactive metabolites. To date, approximately 1,000 secondary metabolites have been discovered, which are predominantly produced by the lichen mycobionts. However, despite the extensive studies on production of lichen secondary metabolites, little is known about the responsible biosynthetic gene clusters (BGCs). Here, we identified a putative BGC that is implicated in production of a red pigment, cristazarin (a naphthazarin derivative), in Cladonia metacorallifera. Previously, cristazarin was shown to be specifically induced in growth media containing fructose as a sole carbon source. Thus, we performed transcriptome analysis of C. metacorallifera growing on different carbon sources including fructose to identify the BGC for cristazarin. Among 39 polyketide synthase (PKS) genes found in the genome of C. metacorallifera, a non-reducing PKS (coined crz7) was highly expressed in growth media containing either fructose or glucose. The borders of a cristazarin gene cluster were delimited by co-expression patterns of neighboring genes of the crz7. BGCs highly conserved to the cristazarin BGC were also found in C. borealis and C. macilenta, indicating that these related species also have metabolic potentials to produce cristazarin. Phylogenetic analysis revealed that the Crz7 is sister to fungal PKSs that biosynthesize an acetylated tetrahydoxynaphthalene as a precursor of melanin pigment. Based on the phylogenetic placement of the Crz7 and putative functions of its neighboring genes, we proposed a plausible biosynthetic route for cristazarin. In this study, we identified a lichen-specific BGC that is likely involved in the biosynthesis of a naphthazarin derivative, cristazarin, and confirmed that transcriptome profiling under inducing and non-inducing conditions is an effective strategy for linking metabolites of interest to biosynthetic genes.

How to build a lichen: from metabolite release to symbiotic interplay

Exposing their vegetative bodies to the light, lichens are outstanding amongst other fungal symbioses. Not requiring a pre-established host, 'lichenized fungi' build an entirely new structure together with microbial photosynthetic partners that neither can form alone. The signals involved in the transition of a fungus and a compatible photosynthetic partner from a free-living to a symbiotic state culminating in thallus formation, termed 'lichenization', and in the maintenance of the symbiosis, are poorly understood. Here, we synthesise the puzzle pieces of the scarce knowledge available into an updated concept of signalling involved in lichenization, comprising five main stages: (1) the 'pre-contact stage', (2) the 'contact stage', (3) 'envelopment' of algal cells by the fungus, (4) their 'incorporation' into a pre-thallus and (5) 'differentiation' into a complex thallus. Considering the involvement of extracellularly released metabolites in each phase, we propose that compounds such as fungal lectins and algal cyclic peptides elicit early contact between the symbionts-to-be, whereas phytohormone signalling, antioxidant protection and carbon exchange through sugars and sugar alcohols are of continued importance throughout all stages. In the fully formed lichen thallus, secondary lichen metabolites and mineral nutrition are suggested to stabilize the functionalities of the thallus, including the associated microbiota.

Stictamycin, an Aromatic Polyketide Antibiotic Isolated from a New Zealand Lichen-Sourced Streptomyces Species

Here we describe the isolation and characterization of stictamycin, a new aromatic polyketide with activity against Staphylococcus aureus. Stictamycin was identified following metabolic profiling and bioactivity guided fractionation of organic extracts from Streptomyces sp. 438-3, an isolate from the New Zealand lichen Sticta felix. Comprehensive 1D and 2D NMR analyses were performed to determine the planar structure of stictamycin and relative configurations of stereo centers, with subsequent comparison of experimental and theoretical ECD spectra allowing elucidation of the absolute configuration. Whole-genome sequencing and biosynthetic gene cluster (BGC) analysis revealed that the Streptomyces sp. 438-3 strain contains an atypical type II polyketide (T2PKS) BGC capable of assembling polycyclic-aromatic ring skeletons. Cloning and knockout studies of this T2PKS BGC were used to confirm that it is responsible for the biosynthesis of stictamycin and elucidate a plausible biosynthetic scheme.

Accumulation of Cadmium in Transplanted Lichen Pyxine cocoes (Sw.) Nyl., with Reference to Physiochemical Variation and Kinetics of Cadmium Biosorption

The present study aims to signify the role of Pyxine cocoes (Sw.) Nyl. (P. cocoes) as cadmium (Cd) biomonitor in atmosphere. This was achieved by quantifying the amount of Cd accumulated in transplanted P. cocoes, when stimulated with known concentrations of Cd (5µM, 50µM, 100µM, 150µM and 200µM) at increasing intervals of time up-to 40 days. All the five concentrations exhibited increasing trend of accumulation with time. As depicted by Pearson's Correlation (at p < 0.001), anti-oxidative enzymes (superoxide dismutase r= -0.812, ascorbate peroxidase r= -0.802, catalase r= -0.757) and electrical conductivity (r = 0.693) were the most efficient parameters to depict increased Cd presence in atmosphere. In the current study, accumulation of Cd by transplanted lichen has been first time analyzed by biosorption kinetics. The uptake of Cd by P. cocoes followed pseudo-second-order kinetics (range of R₂² value was 0.969-0.998). The marker parameters in combination with the ability to accrue Cd fortifies P. cocoes's role as a biomonitor.

Regionally Varying Habitat Relationships in Lichens: The Concept and Evidence with an Emphasis on North-Temperate Ecosystems

Habitat ecology of lichens (lichen-forming fungi) involves diverse adaptations to stressful environments where lichens use specific habitat conditions. Field observations confirm that such habitat ‘preferences’ can vary significantly across species’ distribution ranges, sometimes revealing abrupt changes over short distances. We critically review and generalize such empirical evidence as broad ecological patterns, link these with the likely physiological mechanisms and evolutionary processes involved, and outline the implications for lichen conservation. Non-replicated correlative studies remain only suggestive because the data are frequently compromised by sampling bias and pervasive random errors; further noise is related to unrecognized cryptic species. Replicated evidence exists for three macroecological patterns: (a) regional limiting factors excluding a species from a part of its microhabitat range in suboptimal areas; (b) microhabitat shifts to buffer regionally adverse macroclimates; (c) substrate suitability changed by the chemical environment, notably air pollution. All these appear to be primarily buffering physiological challenges of the adverse conditions at the macrohabitat scale or, in favorable environments, coping with competition or predation. The roles of plasticity, adaptation, dispersal, and population-level stochasticity remain to be studied. Although lichens can inhabit various novel microhabitats, there is no evidence for a related adaptive change. A precautionary approach to lichen conservation is to maintain long-term structural heterogeneity in lichen habitats, and consider lichen ecotypes as potential evolutionarily significant units and a bet-hedging strategy for addressing the climate change-related challenges to biodiversity.

Effect of evernic acid on human breast cancer MCF-7 and MDA-MB-453 cell lines via thioredoxin reductase 1: A molecular approach

Thioredoxin reductase 1 (TrxR1) has emerged as an important target for anticancer drug development due to its overexpression in many human tumors including breast cancer. Due to the serious side effects of currently used commercial anticancer drugs, new natural compounds with very few side effects and high efficacy are of great importance in cancer treatment. Lichen secondary metabolites, known as natural compounds, have diverse biological properties, including antioxidant and anticancer activities. Herein, we aimed to determine the potential antiproliferative, antimigratory, and apoptotic effects of evernic acid, a lichen secondary metabolite, on breast cancer MCF-7 and MDA-MB-453 cell lines and afterward to investigate whether its anticancer effect is exerted by TrxR1-targeting. The cytotoxicity results indicated that evernic acid suppressed the proliferation of MCF-7 and MDA-MB-453 cells in a dose-dependent manner and the IC₅₀ values were calculated as 33.79 and 121.40 μg/mL, respectively. Migration assay results revealed the notable antimigratory ability of evernic acid against both cell types. The expression of apoptotic markers Bcl2 associated X, apoptosis regulator, Bcl2 apoptosis regulator, and tumor protein p53 by quantitative real-time polymerase chain reaction and western blot analysis showed that evernic acid did not induce apoptosis in both cell lines, consistent with flow cytometry results. Evernic acid showed its anticancer effect via inhibiting TrxR1 enzyme activity rather than mRNA and protein expression levels in both cell lines. In conclusion, these findings suggest that evernic acid has the potential to be evaluated as a therapeutic agent in breast cancer treatment.

Genomic Analysis of the Xanthoria elegans and Polyketide Synthase Gene Mining Based on the Whole Genome

Xanthoria elegans is a lichen symbiosis, that inhabits extreme environments and can absorb UV-B. We reported the de novo sequencing and assembly of X. elegans genome. The whole genome was approximately 44.63 Mb, with a GC content of 40.69%. Genome assembly generated 207 scaffolds with an N50 length of 563,100 bp, N90 length of 122,672 bp. The genome comprised 9,581 genes, some encoded enzymes involved in the secondary metabolism such as terpene, polyketides. To further understand the UV-B absorbing and adaptability to extreme environments mechanisms of X. elegans, we searched the secondary metabolites genes and gene-cluster from the genome using genome-mining and bioinformatics analysis. The results revealed that 7 NR-PKSs, 12 HR-PKSs and 2 hybrid PKS-PKSs from X. elegans were isolated, they belong to Type I PKS (T1PKS) according to the domain architecture; phylogenetic analysis and BGCs comparison linked the putative products to two NR-PKSs and three HR-PKSs, the putative products of two NR-PKSs were emodin xanthrone (most likely parietin) and mycophelonic acid, the putative products of three HR-PKSs were soppilines, (+)-asperlin and macrolactone brefeldin A, respectively. 5 PKSs from X. elegans build a correlation between the SMs carbon skeleton and PKS genes based on the domain architecture, phylogenetic and BGC comparison. Although the function of 16 PKSs remains unclear, the findings emphasize that the genes from X. elegans represent an unexploited source of novel polyketide and utilization of lichen gene resources.

A Genomic Survey of the Natural Product Biosynthetic Potential of Actinomycetes Isolated from New Zealand Lichens

Actinomycetes are prolific producers of industrially valuable and medically important compounds. Historically, the most efficient method of obtaining compounds has been bioactivity-guided isolation and characterization of drug-like molecules from culturable soil actinomycetes. Unfortunately, this pipeline has been met with an increasing number of rediscoveries, to the point where it is no longer considered an attractive approach for drug discovery. To address this challenge and to continue finding new compounds, researchers have increasingly focused on alternative environmental niches and screening methods. Here, we report the genetic investigation of actinomycetes from an underexplored source, New Zealand lichens. In this work, we obtain draft genome sequences for 322 lichen-associated actinomycetes. We then explore this genetic resource with an emphasis on biosynthetic potential. By enumerating biosynthetic gene clusters (BGCs) in our data sets and comparing these to various reference collections, we demonstrate that actinomycetes sourced from New Zealand lichens have the genetic capacity to produce large numbers of natural products, many of which are expected to be broadly different from those identified in previous efforts predominantly based on soil samples. Our data shed light on the actinomycete assemblage in New Zealand lichens and demonstrate that lichen-sourced actinobacteria could serve as reservoirs for discovering new secondary metabolites. IMPORTANCE Lichens are home to complex and distinctive microbial cohorts that have not been extensively explored for the ability to produce novel secondary metabolites. Here, we isolate and obtain genome sequence data for 322 actinomycetes from New Zealand lichens. In doing so, we delineate at least 85 potentially undescribed species, and show that lichen associated actinomycetes have the potential to yield many new secondary metabolites, and as such, might serve as a productive starting point for drug discovery efforts.

Screening Evaluation of Antiproliferative, Antimicrobial and Antioxidant Activity of Lichen Extracts and Secondary Metabolites In Vitro

Lichen metabolites represent a wide range of substances with a variety of biological effects. The present study was designed to analyze the potential antiproliferative, antimicrobial and antioxidative effects of several extracts from lichens (Pseudevernia furfuracea, Lobaria pulmonaria, Cetraria islandica, Evernia prunastri, Stereocaulon tomentosum, Xanthoria elegans and Umbilicaria hirsuta) and their secondary metabolites (atranorin, physodic acid, evernic acid and gyrophoric acid). The crude extract, as well as the isolated metabolites, showed potent antiproliferative, cytotoxic activity on a broad range of cancer cell lines in 2D (monolayer) and 3D (spheroid) models. Furthermore, antioxidant (2,2-diphenyl-1-picryl-hydrazylhydrate (DPPH) and in vitro antimicrobial activities were assessed. Data showed that the lichen extracts, as well as the compounds present, possessed biological potential in the studied assays. It was also observed that the extracts were more efficient and their major compounds showed strong effects as antiproliferative, antioxidant and antibacterial agents. Moreover, we demonstrated the 2D and 3D models' importance to drug discovery for further in vivo studies. Despite the fact that lichen compounds have been neglected by the scientific community for long periods, nowadays they are objects of investigation based on their promising effects.

Linking Lichen Metabolites to Genes: Emerging Concepts and Lessons from Molecular Biology and Metagenomics

Lichen secondary metabolites have tremendous pharmaceutical and industrial potential. Although more than 1000 metabolites have been reported from lichens, less than 10 have been linked to the genes coding them. The current biosynthetic research focuses strongly on linking molecules to genes as this is fundamental to adapting the molecule for industrial application. Metagenomic-based gene discovery, which bypasses the challenges associated with culturing an organism, is a promising way forward to link secondary metabolites to genes in non-model, difficult-to-culture organisms. This approach is based on the amalgamation of the knowledge of the evolutionary relationships of the biosynthetic genes, the structure of the target molecule, and the biosynthetic machinery required for its synthesis. So far, metagenomic-based gene discovery is the predominant approach by which lichen metabolites have been linked to their genes. Although the structures of most of the lichen secondary metabolites are well-documented, a comprehensive review of the metabolites linked to their genes, strategies implemented to establish this link, and crucial takeaways from these studies is not available. In this review, I address the following knowledge gaps and, additionally, provide critical insights into the results of these studies, elaborating on the direct and serendipitous lessons that we have learned from them.

Lichen Depsides and Tridepsides: Progress in Pharmacological Approaches

Depsides and tridepsides are secondary metabolites found in lichens. In the last 10 years, there has been a growing interest in the pharmacological activity of these compounds. This review aims to discuss the research findings related to the biological effects and mechanisms of action of lichen depsides and tridepsides. The most studied compound is atranorin, followed by gyrophoric acid, diffractaic acid, and lecanoric acid. Antioxidant, cytotoxic, and antimicrobial activities are among the most investigated activities, mainly in in vitro studies, with occasional in silico and in vivo studies. Clinical trials have not been conducted using depsides and tridepsides. Therefore, future research should focus on conducting more in vivo work and clinical trials, as well as on evaluating the other activities. Moreover, despite the significant increase in research work on the pharmacology of depsides and tridepsides, there are many of these compounds which have yet to be investigated (e.g., hiascic acid, lassalic acid, ovoic acid, crustinic acid, and hypothamnolic acid).

Recent advances in research for potential utilization of unexplored lichen metabolites

Several research studies have shown that lichens are productive organisms for the synthesis of a broad range of secondary metabolites. Lichens are a self-sustainable stable microbial ecosystem comprising an exhabitant fungal partner (mycobiont) and at least one or more photosynthetic partners (photobiont). The successful symbiosis is responsible for their persistence throughout time and allows all the partners (holobionts) to thrive in many extreme habitats, where without the synergistic relationship they would be rare or non-existent. The ability to survive in harsh conditions can be directly correlated with the production of some unique metabolites. Despite the potential applications, these unique metabolites have been underutilised by pharmaceutical and agrochemical industries due to their slow growth, low biomass availability and technical challenges involved in their artificial cultivation. However, recent development of biotechnological tools such as molecular phylogenetics, modern tissue culture techniques, metabolomics and molecular engineering are opening up a new opportunity to exploit these compounds within the lichen holobiome for industrial applications. This review also highlights the recent advances in culturing the symbionts and the computational and molecular genetics approaches of lichen gene regulation recognized for the enhanced production of target metabolites. The recent development of multi-omics novel biodiscovery strategies aided by synthetic biology in order to study the heterologous expressed lichen-derived biosynthetic gene clusters in a cultivatable host offers a promising means for a sustainable supply of specialized metabolites.

Green ultrasound-assisted extraction of lichen substances from Hypotrachyna cirrhata. Ethyl lactate, a better extracting agent than methanol toxic organic solvent?

For the first time, we report a green extraction of lichen substances assisted by high power ultrasounds from Hypotrachyna cirrhata using ethyl lactate. This sustainable alternative was comparable, both in isolation and detection of lichen substances, to methanol. In the metabolomic analysis, a total of 77 lichen substances were detected comprising depsides, depsidones, dibenzofurans, organic acids, and lipids. Although the UHPLC/ESI/MS profiles were similar, the antioxidant activity was higher for the ethyl lactate extract. Ethyl lactate can replace toxic organic solvents, such as methanol, in order to provide more sustainable green chemistry methods.

Discovery of Pan-peroxisome Proliferator-Activated Receptor Modulators from an Endolichenic Fungus, Daldinia childiae

Adiponectin-synthesis-promoting compounds possess therapeutic potential to treat diverse metabolic diseases, including obesity and diabetes. Phenotypic screening to find adiponectin-synthesis-promoting compounds was performed using the adipogenesis model of human bone marrow mesenchymal stem cells. The extract of the endolichenic fungus Daldinia childiae 047215 significantly promoted adiponectin production. Bioactivity-guided isolation led to 13 active polyketides (1-13), which include naphthol monomers, dimers, and trimers. To the best of our knowledge, trimers of naphthol (1-4) have not been previously isolated as either natural or synthetic products. The novel naphthol trimer 3,1',3',3″-ternaphthalene-5,5',5″-trimethoxy-4,4',4″-triol (2) and a dimer, nodulisporin A (12), exhibited concentration-dependent adiponectin-synthesis-promoting activity (EC₅₀ 30.8 and 15.2 μM, respectively). Compounds 2 and 12 bound to all three peroxisome proliferator-activated receptor (PPAR) subtypes, PPARα, PPARγ, and PPARδ. In addition, compound 2 transactivated retinoid X receptor α, whereas 12 did not. Naphthol oligomers 2 and 12 represent novel pan-PPAR modulators and are potential pharmacophores for designing new therapeutic agents against hypoadiponectinemia-associated metabolic diseases.

New Strain of Cyphellophora olivacea Exhibits Striking Tolerance to Sodium Bicarbonate

The cyanobacterium strain Synechococcus cedrorum SAG 88.79 stock culture has fungal contamination stated by the Sammlung von Algenkulturen der Universität Göttingen itself. In this recent work, this particular fungal strain was isolated, identified, and morphologically characterised. The fungal strain AGSC12 belongs to the species Cyphellophora olivacea, with respect to the sequence similarity, phylogeny, and morphology of the strain. Colony morphology and growth capability were examined on SMA, EMMA, PDA, MEA, YEA, and YPA plates. Growth of the colonies was the most successful on YPA plates, followed by PDA and MEA containing plates. Surprisingly, the AGSC12 strain showed extreme tolerance to NaHCO3, albeit it, is is considered a general fungistatic compound. Moreover, positive association between the AGSC12 and SAG 88.79 strains was revealed, as the SAG 88.79 strain always attained higher cell density in co-cultures with the fungus than in mono-cultures. Besides, a taxonomic note on the SAG 88.79 strain itself was also stated.

Metabolomic Profiling, Antioxidant and Enzyme Inhibition Properties and Molecular Docking Analysis of Antarctic Lichens

The lichen species Lecania brialmontii, Pseudephebe pubescens, and Sphaerophorus globosus are part of the prominent lichenoflora of the Antarctic territory. In this work, we report the metabolomic identification of ethanolic extracts of these species, their antioxidant and cholinesterase enzyme inhibitory activity, and conduct a molecular docking analysis with typical compounds. Eighteen compounds were identified by UHPLC-ESI-QTOF-MS in L. brialmontii, 18 compounds in P. pubescens, and 14 compounds in S. globosus. The content of phenolic compounds was variable among the species, ranging from 0.279 to 2.821 mg AG/g, and all three species showed high inhibition potential on the cholinesterase enzymes. Molecular docking showed important interactions between AChE and BChE with the selected compounds. This study evidences the chemical fingerprint of three species of the order Lecanorales that support the continuation of the study of other biological activities and their potential for medical research.

Genome mining as a biotechnological tool for the discovery of novel biosynthetic genes in lichens

Natural products (NPs) and their derivatives are a major contributor to modern medicine. Historically, microorganisms such as bacteria and fungi have been instrumental in generating drugs and lead compounds because of the ease of culturing and genetically manipulating them. However, the ever-increasing demand for novel drugs highlights the need to bioprospect previously unexplored taxa for their biosynthetic potential. Next-generation sequencing technologies have expanded the range of organisms that can be explored for their biosynthetic content, as these technologies can provide a glimpse of an organism's entire biosynthetic landscape, without the need for cultivation. The entirety of biosynthetic genes can be compared to the genes of known function to identify the gene clusters potentially coding for novel products. In this study, we mine the genomes of nine lichen-forming fungal species of the genus Umbilicaria for biosynthetic genes, and categorize the biosynthetic gene clusters (BGCs) as "associated product structurally known" or "associated product putatively novel". Although lichen-forming fungi have been suggested to be a rich source of NPs, it is not known how their biosynthetic diversity compares to that of bacteria and non-lichenized fungi. We found that 25%-30% of biosynthetic genes are divergent as compared to the global database of BGCs, which comprises 1,200,000 characterized biosynthetic genes from plants, bacteria, and fungi. Out of 217 BGCs, 43 were highly divergant suggesting that they potentially encode structurally and functionally novel NPs. Clusters encoding the putatively novel metabolic diversity comprise polyketide synthases (30), non-ribosomal peptide synthetases (12), and terpenes (1). Our study emphasizes the utility of genomic data in bioprospecting microorganisms for their biosynthetic potential and in advancing the industrial application of unexplored taxa. We highlight the untapped structural metabolic diversity encoded in the lichenized fungal genomes. To the best of our knowledge, this is the first investigation identifying genes coding for NPs with potentially novel properties in lichenized fungi.

Lichen Extracts from Cetrarioid Clade Provide Neuroprotection against Hydrogen Peroxide-Induced Oxidative Stress

Oxidative stress is involved in the pathophysiology of many neurodegenerative diseases. Lichens have antioxidant properties attributed to their own secondary metabolites with phenol groups. Very few studies delve into the protective capacity of lichens based on their antioxidant properties and their action mechanism. The present study evaluates the neuroprotective role of Dactylina arctica, Nephromopsis stracheyi, Tuckermannopsis americana and Vulpicida pinastri methanol extracts in a hydrogen peroxide (H₂O₂) oxidative stress model in neuroblastoma cell line "SH-SY5Y cells". Cells were pretreated with different concentrations of lichen extracts (24 h) before H₂O₂ (250 µM, 1 h). Our results showed that D. arctica (10 µg/mL), N. stracheyi (25 µg/mL), T. americana (50 µg/mL) and V. pinastri (5 µg/mL) prevented cell death and morphological changes. Moreover, these lichens significantly inhibited reactive oxygen species (ROS) production and lipid peroxidation and increased superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) levels. Furthermore, they attenuated mitochondrial membrane potential decline and calcium homeostasis disruption. Finally, high-performance liquid chromatography (HPLC) analysis revealed that the secondary metabolites were gyrophoric acid and lecanoric acid in D. artica, usnic acid, pinastric acid and vulpinic acid in V. pinastri, and alectoronic acid in T. americana. In conclusion, D. arctica and V. pinastri are the most promising lichens to prevent and to treat oxidative stress-related neurodegenerative diseases.

Potential human health risks of toxic/harmful elements by consumption of Pseudevernia furfuracea

The potential human health risks of some toxic/harmful elements related to the consumption of Pseudevernia furfuracea (L.) Zopf. were investigated. The toxic/harmful elements (cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni), and zinc (Zn)) were determined in P. furfuracea. According to the analysis result, the maximum (max.) toxic/harmful element value was 62 ± 3.1 mg/kg for Mn and minimum (min.) value was 0.19 ± 0.01 mg/kg for Cd. The estimated daily exposure doses (EDEXDs) for men, women and children were dietary (bread) > dietary (tea) > dermal. For dietary (bread) and dietary (tea) non-carcinogenic (HQ) risk was children > women > men. For dermal, HQ risk was women > children > men. Hazard index (HI) value for men was >1 for Cr. HI value for men was 1.36 for Cr. HI value for women was >1 for Cr and Mn. HI values for women were 1.54 for Cr and 1.01 for Mn. Also, the HI value for children was >1 for Cr, Mn, and Pb. HI values for children were 3.44 for Cr, 2.24 for Mn, and 1.66 for Pb. This situation showed that there was a non-carcinogenic risk. Carcinogenic risk values were dietary (bread) > dietary (tea) > dermal. The total max. carcinogenic value was 1.97E-03 for Cr while the total min. carcinogenic value was 1.31E-05 for Pb. As a result, it has been determined that there may be a risk of cancer due to the consumption of lichen as bread and this situation may adversely affect human health.

Lichen Depsidones with Biological Interest

Depsidones are some of the most abundant secondary metabolites produced by lichens. These compounds have aroused great pharmacological interest due to their activities as antioxidants, antimicrobial, and cytotoxic agents. Hence, this paper aims to provide up-to-date knowledge including an overview of the potential biological interest of lichen depsidones. So far, the most studied depsidones are fumarprotocetraric acid, lobaric acid, norstictic acid, physodic acid, salazinic acid, and stictic acid. Their pharmacological activities have been mainly investigated in in vitro studies and, to a lesser extent, in in vivo studies. No clinical trials have been performed yet. Depsidones are promising cytotoxic agents that act against different cell lines of animal and human origin. Moreover, these compounds have shown antimicrobial activity against both Gram-positive and Gram-negative bacteria and fungi, mainly Candida spp. Furthermore, depsidones have antioxidant properties as revealed in oxidative stress in vitro and in vivo models. Future research should be focused on further investigating the mechanism of action of depsidones and in evaluating new potential actions as well as other depsidones that have not been studied yet from a pharmacological perspective. Likewise, more in vivo studies are prerequisite, and clinical trials for the most promising depsidones are encouraged.

The Genus Cetraria s. str.-A Review of Its Botany, Phytochemistry, Traditional Uses and Pharmacology

The genus Cetraria s. str. (Parmeliaceae family, Cetrarioid clade) consists of 15 species of mostly erect brown or greenish yellow fruticose or subfoliose thallus. These Cetraria species have a cosmopolitan distribution, being primarily located in the Northern Hemisphere, in North America and in the Eurasia area. Phytochemical analysis has demonstrated the presence of dibenzofuran derivatives (usnic acid), depsidones (fumarprotocetraric and protocetraric acids) and fatty acids (lichesterinic and protolichesterinic acids). The species of Cetraria, and more particularly Cetraria islandica, has been widely employed in folk medicine for the treatment of digestive and respiratory diseases as decoctions, tinctures, aqueous extract, and infusions. Moreover, Cetraria islandica has had an important nutritional and cosmetic value. These traditional uses have been validated in in vitro and in vivo pharmacological studies. Additionally, new therapeutic activities are being investigated, such as antioxidant, immunomodulatory, cytotoxic, genotoxic and antigenotoxic. Among all Cetraria species, the most investigated by far has been Cetraria islandica, followed by Cetraria pinastri and Cetraria aculeata. The aim of the current review is to update all the knowledge about the genus Cetraria covering aspects that include taxonomy and phylogeny, morphology and distribution, ecological and environmental interest, phytochemistry, traditional uses and pharmacological properties.

A call to reconceptualize lichen symbioses

Several decades of research across disciplines have overturned historical perspectives of symbioses dominated by binary characterizations of highly specific species-species interactions. This paradigm shift has unlocked the previously underappreciated and overlooked dynamism of fungal mutualisms such as mycorrhizae. Lichens are another example of important fungal mutualisms where reconceptualization is urgently needed to realize their potential as model systems. This reconceptualization requires both an objective synthesis of new data and envisioning a revised integrative approach that unifies the spectrum of ecology and evolution. We propose a ten-theme framework that if pursued would propel lichens to the vanguard of symbiotic theory.

Peltigera frigida Lichens and Their Substrates Reduce the Influence of Forest Cover Change on Phosphate Solubilizing Bacteria

Phosphorus (P) is one of the most critical macronutrients in forest ecosystems. More than 70 years ago, some Chilean Patagonian temperate forests suffered wildfires and the subsequent afforestation with foreign tree species such as pines. Since soil P turnover is interlinked with the tree cover, this could influence soil P content and bioavailability. Next to soil microorganisms, which are key players in P transformation processes, a vital component of Patagonian temperate forest are lichens, which represent microbial hotspots for bacterial diversity. In the present study, we explored the impact of forest cover on the abundance of phosphate solubilizing bacteria (PSB) from three microenvironments of the forest floor: Peltigera frigida lichen thallus, their underlying substrates, and the forest soil without lichen cover. We expected that the abundance of PSB in the forest soil would be strongly affected by the tree cover composition since the aboveground vegetation influences the edaphic properties; but, as P. frigida has a specific bacterial community, lichens would mitigate this impact. Our study includes five sites representing a gradient in tree cover types, from a mature forest dominated by the native species Nothofagus pumilio, to native second-growth forests with a gradual increase in the presence of Pinus contorta in the last sites. In each site, we measured edaphic parameters, P fractions, and the bacterial potential to solubilize phosphate by quantifying five specific marker genes by qPCR. The results show higher soluble P, labile mineral P, and organic matter in the soils of the sites with a higher abundance of P. contorta, while most of the molecular markers were less abundant in the soils of these sites. Contrarily, the abundance of the molecular markers in lichens and substrates was less affected by the tree cover type. Therefore, the bacterial potential to solubilize phosphate is more affected by the edaphic factors and tree cover type in soils than in substrates and thalli of P. frigida lichens. Altogether, these results indicate that the microenvironments of lichens and their substrates could act as an environmental buffer reducing the influence of forest cover composition on bacteria involved in P turnover.

A comparative genomic analysis of lichen-forming fungi reveals new insights into fungal lifestyles

Lichen-forming fungi are mutualistic symbionts of green algae or cyanobacteria. We report the comparative analysis of six genomes of lichen-forming fungi in classes Eurotiomycetes and Lecanoromycetes to identify genomic information related to their symbiotic lifestyle. The lichen-forming fungi exhibited genome reduction via the loss of dispensable genes encoding plant-cell-wall-degrading enzymes, sugar transporters, and transcription factors. The loss of these genes reflects the symbiotic biology of lichens, such as the absence of pectin in the algal cell wall and obtaining specific sugars from photosynthetic partners. The lichens also gained many lineage- and species-specific genes, including those encoding small secreted proteins. These genes are primarily induced during the early stage of lichen symbiosis, indicating their significant roles in the establishment of lichen symbiosis.Our findings provide comprehensive genomic information for six lichen-forming fungi and novel insights into lichen biology and the evolution of symbiosis.

Modulation of Cellular Circadian Rhythms by Secondary Metabolites of Lichens

Background

Most mammalian cells harbor molecular circadian clocks that synchronize physiological functions with the 24-h day-night cycle. Disruption of circadian rhythms, through genetic or environmental changes, promotes the development of disorders like obesity, cardiovascular diseases, and cancer. At the cellular level, circadian, mitotic, and redox cycles are functionally coupled. Evernic (EA) and usnic acid (UA), two lichen secondary metabolites, show various pharmacological activities including anti-oxidative, anti-inflammatory, and neuroprotective action. All these effects have likewise been associated with a functional circadian clock.

Hypothesis/Purpose

To test, if the lichen compounds EA and UA modulate circadian clock function at the cellular level.

Methods

We used three different cell lines and two circadian luminescence reporter systems for evaluating dose- and time-dependent effects of EA/UA treatment on cellular clock regulation at high temporal resolution. Output parameters studied were circadian luminescence rhythm period, amplitude, phase, and dampening rate.

Results

Both compounds had marked effects on clock rhythm amplitudes and dampening independent of cell type, with UA generally showing a higher efficiency than EA. Only in fibroblast cells, significant effects on clock period were observed for UA treated cells showing shorter and EA treated cells showing longer period lengths. Transient treatment of mouse embryonic fibroblasts at different phases had only minor clock resetting effects for both compounds.

Conclusion

Secondary metabolites of lichen alter cellular circadian clocks through amplitude reduction and increased rhythm dampening.

Intramolecular transesterification of depsides yields fluorescent 1H-isochromen-1-ones: Application as a chemical probe for lichen determination

The reactivity of eight purified depsides obtained from six european lichens and that display as 2-oxoalkyl chain in ortho-position of the ester bond was explored. These depsides were found to lead to 1H-Isochromen-1-ones, which exhibit a distinctive blue fluorescence at 365 nm, in the presence of a 10% aqueous solution of KOH. A mechanistic explanation, involving the formation of an enolate intermediate and intramolecular transesterification, was proposed and validated by DFT. By exploiting this fluorescent phenomenon, we conceived a chemical probe (the KUV probe) that is useful for lichen determination, as exemplified on a selection of European Porpidia species.

Metabolite Profiling in Green Microalgae with Varying Degrees of Desiccation Tolerance

Trebouxiophyceae are microalgae occupying even extreme environments such as polar regions or deserts, terrestrial or aquatic, and can occur free-living or as lichen photobionts. Yet, it is poorly understood how environmental factors shape their metabolism. Here, we report on responses to light and temperature, and metabolic adjustments to desiccation in Diplosphaera epiphytica, isolated from a lichen, and Edaphochlorella mirabilis, isolated from Tundra soil, assessed via growth and photosynthetic performance parameters. Metabolite profiling was conducted by GC–MS. A meta-analysis together with data from a terrestrial and an aquatic Chlorella vulgaris strain reflected elements of phylogenetic relationship, lifestyle, and relative desiccation tolerance of the four algal strains. For example, compatible solutes associated with desiccation tolerance were up-accumulated in D. epiphytica, but also sugars and sugar alcohols typically produced by lichen photobionts. The aquatic C. vulgaris, the most desiccation-sensitive strain, showed the greatest variation in metabolite accumulation after desiccation and rehydration, whereas the most desiccation-tolerant strain, D. epiphytica, showed the least, suggesting that it has a more efficient constitutive protection from desiccation and/or that desiccation disturbed the metabolic steady-state less than in the other three strains. The authors hope that this study will stimulate more research into desiccation tolerance mechanisms in these under-investigated microorganisms.

Phylogenetic Studies and Metabolite Analysis of Sticta Species from Colombia and Chile by Ultra-High Performance Liquid Chromatography-High Resolution-Q-Orbitrap-Mass Spectrometry

Eleven species of lichens of the genus Sticta, ten of which were collected in Colombia (S. pseudosylvatica S. luteocyphellata S. cf. andina S. cf. hypoglabra, S. cordillerana, S. cf. gyalocarpa S. leucoblepharis, S. parahumboldtii S. impressula, S. ocaniensis) and one collected in Chile (S. lineariloba), were analyzed for the first time using hyphenated liquid chromatography with high-resolution mass spectrometry. In the metabolomic analysis, a total of 189 peaks were tentatively detected; the analyses were divided in five (5) groups of compounds comprising lipids, small phenolic compounds, saturated acids, terpenes, and typical phenolic lichen compounds such as depsides, depsidones and anthraquinones. The metabolome profiles of these eleven species are important since some compounds were identified as chemical markers for the fast identification of Sticta lichens for the first time. Finally, the usefulness of chemical compounds in comparison to traditional morphological traits to the study of ancestor–descendant relationships in the genus was assessed. Chemical and morphological consensus trees were not consistent with each other and recovered different relationships between taxa.