Modelling the carbon balance in bryophytes and lichens: Presentation of PoiCarb 1.0, a new model for explaining distribution patterns and predicting climate-change effects

PREMISE

Bryophytes and lichens have important functional roles in many ecosystems. Insight into their CO2 -exchange responses to climatic conditions is essential for understanding current and predicting future productivity and biomass patterns, but responses are hard to quantify at time scales beyond instantaneous measurements. We present PoiCarb 1.0, a model to study how CO2 -exchange rates of these poikilohydric organisms change through time as a function of weather conditions.

METHODS

PoiCarb simulates diel fluctuations of CO2 exchange and estimates long-term carbon balances, identifying optimal and limiting climatic patterns. Modelled processes were net photosynthesis, dark respiration, evaporation and water uptake. Measured CO2 -exchange responses to light, temperature, atmospheric CO2 concentration, and thallus water content (calculated in a separate module) were used to parameterize the model's carbon module. We validated the model by comparing modelled diel courses of net CO2 exchange to such courses from field measurements on the tropical lichen Crocodia aurata. To demonstrate the model's usefulness, we simulated potential climate-change effects.

RESULTS

Diel patterns were reproduced well, and the modelled and observed diel carbon balances were strongly positively correlated. Simulated warming effects via changes in metabolic rates were consistently negative, while effects via faster drying were variable, depending on the timing of hydration.

CONCLUSIONS

Reproducing weather-dependent variation in diel carbon balances is a clear improvement compared to simply extrapolating short-term measurements or potential photosynthetic rates. Apart from predicting climate-change effects, future uses of PoiCarb include testing hypotheses about distribution patterns of poikilohydric organisms and guiding conservation strategies for species.

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.

Salazinic Acid and Norlobaridone from the Lichen Hypotrachyna cirrhata: Antioxidant Activity, α-Glucosidase Inhibitory and Molecular Docking Studies

The present study was intended for the identification of secondary metabolites in acetone extract of the lichen Hypotrachyna cirrhata using UPLC-ESI-QToF-MS/MS and the detection of bioactive compounds. This study led to the identification of 22 metabolites based on their MS/MS spectra, accurate molecular masses, molecular formula from a comparison of the literature database (DNP), and fragmentation patterns. In addition, potent antioxidant and α-glucosidase inhibitory potentials of acetone extract of H. cirrhata motivated us to isolate 10 metabolites, which were characterized as salazinic acid (11), norlobaridone (12), atranorin (13), lecanoric acid (14), lichesterinic acid (15), protolichesterinic acid (16), methyl hematommate (17), iso-rhizonic acid (18), atranol (19), and methylatratate (20) based on their spectral data. All these isolates were assessed for their free radicals scavenging, radical-induced DNA damage, and intestinal α-glucosidase inhibitory activities. The results indicated that norlobaridone (12), lecanoric acid (14), methyl hematommate (17), and atranol (19) showed potent antioxidant activity, while depsidones (salazinic acid (11), norlobaridone (12)) and a monophenolic compound (iso-rhizonic acid, (18)) displayed significant intestinal α-glucosidase inhibitory activities (p < 0.001), which is comparable to standard acarbose. These results were further correlated with molecular docking studies, which indicated that the alkyl chain of norlobaridione (12) is hooked into the finger-like cavity of the allosteric pocket; moreover, it also established Van der Waals interactions with hydrophobic residues of the allosteric pocket. Thus, the potency of norlobaridone to inhibit α-glucosidase enzyme might be associated with its allosteric binding. Also, MM-GBSA (Molecular Mechanics-Generalized Born Surface Area) binding free energies of salazinic acid (11) and norlobaridone (12) were superior to acarbose and may have contributed to their high activity compared to acarbose.

The Lichen Flavin-Dependent Halogenase, DnHal: Identification, Heterologous Expression and Functional Characterization

Enzymatic halogenation captures scientific interest considering its feasibility in modifying compounds for chemical diversity. Currently, majority of flavin-dependent halogenases (F-Hals) were reported from bacterial origin, and as far as we know, none from lichenized fungi. Fungi are well-known producers of halogenated compounds, so using available transcriptomic dataset of Dirinaria sp., we mined for putative gene encoding for F-Hal. Phylogenetic-based classification of the F-Hal family suggested a non-tryptophan F-Hals, similar to other fungal F-Hals, which mainly act on aromatic compounds. However, after the putative halogenase gene from Dirinaria sp., dnhal was codon-optimized, cloned, and expressed in Pichia pastoris, the ~63 kDa purified enzyme showed biocatalytic activity towards tryptophan and an aromatic compound methyl haematommate, which gave the tell-tale isotopic pattern of a chlorinated product at m/z 239.0565 and 241.0552; and m/z 243.0074 and 245.0025, respectively. This study is the start of understanding the complexities of lichenized fungal F-hals and its ability to halogenate tryptophan and other aromatic. compounds which can be used as green alternatives for biocatalysis of halogenated compounds.

Modeling and optimization of antibacterial effect of lichen-associated bacteria, Bacillus subtilis KSRLAB3 strain against marine fouling bacteria, Vibrio alginolyticus

One of the most commonly occurring bacteria, Bacillus subtilis, can produce a wide variety of secondary metabolites. In this study, the antimicrobial effect of B. subtilis KSRLAB3 against Vibrio alginolyticus was optimized using the Plackett-Burman design (PBD) method, response surface methodology (RSM), and genetic algorithm (GA). Initially, the effects of carbon source, nitrogen source, NaCl concentration, pH, temperature, and incubation time on antimicrobial effects were studied. Among the carbon and nitrogen sources investigated, mannose and peptone elicited maximum antimicrobial effect. Using PBD, the most significant variables that influence the antimicrobial effect were identified, including incubation time, peptone concentration, and temperature. The optimum conditions required for attaining maximum antimicrobial effect was identified using the RSM-GA hybrid method, and the optimum condition includes 49.999 h of incubation time, 4.39 g/L of peptone concentration, and 27.629°C of incubation temperature. The confirmatory experiments performed around the optimum condition showed a zone of inhibition of 35 ± 0.52 mm. Methanolic extract also proved the presence of antibacterial lipopeptide surfactin. Therefore, the RSM-GA hybrid method was successfully used in this study to model the antimicrobial effect of B. subtilis KSRLAB3 against V. alginolyticus. The effective inhibition of V. alginolyticus can be investigated further for the development of antifouling coatings.

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.

Interaction effect of fungicide and chitosan on non-target lichenized fungi

Excessive use of plant growth stimulants and pesticides is currently a considerable problem, especially in agriculture, horticulture, and arboriculture. Understanding the impacts of these compounds and their combinations on non-target organisms is crucial to minimize unintended consequences, while maintaining their use in plant protection. The aim of this study was to test how long-term spraying with different solutions of natural biostimulator chitosan, synthetic fungicide Switch 62.5 WG, and their combinations affects the physiology of epiphytic lichen Xanthoria parietina naturally occurring in fruit orchards and farmlands. We showed that fungicides composed of fludioxionil and cypronidil, as well as the combined use of such fungicides together with chitosan, can cause the considerable impairment of lichen physiology, and these disturbances relate to both algal and fungal partners of the symbiotic association. This negative effect was especially visible in the loss of cell membrane integrity, the high level of membrane lipid peroxidation, and changes in chlorophyll fluorescence parameters on the last day of the experiment. The combined use of these agents also leads to clear disturbances in the functioning of the mitochondrial respiratory chain, which was manifested by increased NADH dehydrogenase activity, while the use of these compounds separately led to a decrease in the activity of this enzyme. We concluded that the regular use of these agents in fruit tree cultivation may cause serious ecological consequences for epiphytic lichen communities as a result of the death of lichen thalli. This study suggests that the impact of some plant protection agents, both individually and in combinations, merits further attention in terms of their impact on non-target fungi.

Lichen ecophysiology in a changing climate

Lichens are one of the most iconic and ubiquitous symbioses known, widely valued as indicators of environmental quality and, more recently, climate change. Our understanding of lichen responses to climate has greatly expanded in recent decades, but some biases and constraints have shaped our present knowledge. In this review we focus on lichen ecophysiology as a key to predicting responses to present and future climates, highlighting recent advances and remaining challenges. Lichen ecophysiology is best understood through complementary whole-thallus and within-thallus scales. Water content and form (vapor or liquid) are central to whole-thallus perspectives, making vapor pressure differential (VPD) a particularly informative environmental driver. Responses to water content are further modulated by photobiont physiology and whole-thallus phenotype, providing clear links to a functional trait framework. However, this thallus-level perspective is incomplete without also considering within-thallus dynamics, such as changing proportions or even identities of symbionts in response to climate, nutrients, and other stressors. These changes provide pathways for acclimation, but their understanding is currently limited by large gaps in our understanding of carbon allocation and symbiont turnover in lichens. Lastly, the study of lichen physiology has mainly prioritized larger lichens at high latitudes, producing valuable insights but underrepresenting the range of lichenized lineages and ecologies. Key areas for future work include improving geographic and phylogenetic coverage, greater emphasis on VPD as a climatic factor, advances in the study of carbon allocation and symbiont turnover, and the incorporation of physiological theory and functional traits in our predictive models.

Climate warming causes photobiont degradation and carbon starvation in a boreal climate sentinel lichen

PREMISE

The long-term potential for acclimation by lichens to changing climates is poorly known, despite their prominent roles in forested ecosystems. Although often considered "extremophiles," lichens may not readily acclimate to novel climates well beyond historical norms. In a previous study (Smith et al., 2018), Evernia mesomorpha transplants in a whole-ecosystem climate change experiment showed drastic mass loss after 1 yr of warming and drying; however, the causes of this mass loss were not addressed.

METHODS

We examined the causes of this warming-induced mass loss by measuring physiological, functional, and reproductive attributes of lichen transplants.

RESULTS

Severe loss of mass and physiological function occurred above +2°C of experimental warming. Loss of algal symbionts ("bleaching") and turnover in algal community compositions increased with temperature and were the clearest impacts of experimental warming. Enhanced CO₂ had no significant physiological or symbiont composition effects. The functional loss of algal photobionts led to significant loss of mass and specific thallus mass (STM), which in turn reduced water-holding capacity (WHC). Although algal genotypes remained detectable in thalli exposed to higher stress, within-thallus photobiont communities shifted in composition toward greater diversity.

CONCLUSIONS

The strong negative impacts of warming and/or lower humidity on Evernia mesomorpha were driven by a loss of photobiont activity. Analogous to the effects of climate change on corals, the balance of symbiont carbon metabolism in lichens is central to their resilience to changing conditions.

Two-step isolation of the two major paraconic acids of Cetraria islandica

The lichen Cetraria islandica is traditionally used as a demulcent for the symptomatic treatment of irritations of the mouth and throat and associated dry cough, as well as for the treatment of temporary loss of appetite. In addition to depsides and depsidones, thalli contain paraconic acids, a group of secondary metabolites commonly found in lichens and fungi. Among those, protolichesterinic acid has shown promising pharmacological activities. However, the efficient isolation of paraconic acids is quite complex due to their very similar chemical structures and their weak ultraviolet absorption. In the present work, a two-step isolation protocol of protolichesterinic acid and lichesterinic acid from a complex paraconic acid mixture is described using Sephadex LH20 column chromatography and fast centrifugal partition chromatography. Final purities higher than 95% and recoveries above 50% are achieved. Additionally, reliable qualitative techniques for detecting and differentiating paraconic acids are described. Finally, some data on compound stability and enantiomeric purity are shown.

Unraveling the ameliorative potentials of native lichen Pyxine cocoes (Sw.) Nyl., during COVID 19 phase

Due to the rapid increase in the novel coronavirus virulence, the entire world implemented the practice of lockdown along with the constraint of human movement. The obligation of quarantine halted most of the commercial and industrial movement that prominently disturbed the distinct key environmental parameters directly associated with the plant's and animal's health conditions. In this regard, the research aims to study the sudden shut-off of vehicular activity impact on the naturally growing lichen of the genus Pyxine cocoes. The results showed an increase in the pigments, Fv/Fm ratio, and phytohormones during the lockdown and concurrently the decreasing levels in the post-lockdown period. Interestingly, modulations in the phytohormones occur in the lockdown period as compared to the post-lockdown period. The metals Al, Cr, and Fe show the highest increasing trends in the unlocking period, whereas As, Cd, Pb, Cu, Hg, Mn, and Zn show very little variation during the running and post-lockdown phases. The lichen photosynthetic activity justifies further examination as initial biological indicators of the abrupt environmental variations prompted by such types of atmospheric situations and, to a greater extent, for the risk assessment in the near future. In conclusion, stress-phytohormone and amino acids play a significant role as stress reducers. Although lichens are well known for long environmental assessment, the present study will provide qualitative and quantitative variation in physiochemical changes in the short term and sudden environmental fluctuations. HIGHLIGHTS: • Qualitative and quantitative variation in biochemical parameters in lichen during and post-lockdown period was analyzed. • Stress-phytohormone and amino acids play a significant role as stress reducers. • Selectivity sequence reflection in heavy metal accumulation may be used in future studies.

Towards understanding the effect of heavy metals on mycobiont physiological condition in a widespread metal-tolerant lichen Cladonia rei

Heavy metals present in the environment can cause a variety of injury symptoms in various organisms including lichens. Most studies examined metal-induced stress under controlled laboratory conditions, and little is known about actual response of lichens in their natural habitat. This study aims to recognize the effect of heavy metal accumulation (total and intracellular) on lichen physiological and biochemical parameters specifically related to the functioning of fungal component. Cladonia rei was used as a model species due to its common occurrence both in unpolluted and extremely polluted sites. We observed a decline in the fungal metabolism which was expressed by a decrease in ergosterol content and an increase in cell membrane damage as a result of increased Zn, Cd, Cu and Ni accumulation. Additionally, the results indicated that increased accumulation of xenobiotics (Pb and As) caused reduction of glutathione (GSH) concentrations and increased membrane lipid peroxidation. Therefore, we conclude that GSH does not provide high oxidative stress protection in C. rei which is somewhat against its insensitivity to pollution. The reduced pool of GSH could be explained by its oxidation to glutathione disulphide induced by heavy metal stress or its use for phytochelatin (PC) synthesis. The content of secondary metabolites was not related to heavy metal accumulation and remained at a relatively stable level. This indicates that the decline in the physiological condition did not weaken the mycobiont of C. rei enough to inhibit the synthesis of secondary metabolites and their precursors were supplied at a sufficient level. Thus, the potential function of main secondary metabolites as extracellular metal immobilizers and antioxidants is still possible even in individuals growing at extremely polluted sites. Despite the evident heavy metal stress, C. rei copes well and spreads easily through extremely polluted environments, which underlines its unique pioneering abilities in highly disturbed sites.

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.

Novel methods to characterise spatial distribution and enantiomeric composition of usnic acids in four Icelandic lichens

Usnic acid is an antibiotic metabolite produced by a wide variety of lichenized fungal lineages. The enantiomers of usnic acid have been shown to display contrasting bioactivities, and hence it is important to determine their spatial distribution, amounts and enantiomeric ratios in lichens to understand their roles in nature and grasp their pharmaceutical potential. The overall aim of the study was to characterise the spatial distribution of the predominant usnic acid enantiomer in lichens by combining spatial imaging and chiral chromatography. Specifically, separation and quantification of usnic acid enantiomers in four common lichens in Iceland was performed using a validated chiral chromatographic method. Molecular dynamics simulation was carried out to rationalize the chiral separation mechanism. Spatial distribution of usnic acid in the lichen thallus cross-sections were analysed using Desorption Electrospray Ionization-Imaging Mass Spectrometry (DESI-IMS) and fluorescence microscopy. DESI-IMS confirmed usnic acid as a cortical compound, and revealed that usnic acid can be more concentrated around the algal vicinity. Fluorescence microscopy complemented DESI-IMS by providing more detailed distribution information. By combining results from spatial imaging and chiral separation, we were able to visualize the distribution of the predominant usnic acid enantiomer in lichen cross-sections: (+)-usnic acid in Cladonia arbuscula and Ramalina siliquosa, and (-)-usnic acid in Alectoria ochroleuca and Flavocetraria nivalis. This study provides an analytical foundation for future environmental and functional studies of usnic acid enantiomers in lichens.

Photosynthesis measurements on the upper and lower side of the thallus of the foliose lichen Nephroma arcticum (L.) Torss

The measurements of chlorophyll fluorescence play an important role in studies of lichen physiology. Usually, for foliose lichens fluorescence kinetics is recorded from the upper thalline side often exhibiting green color reflecting the presence of photosynthetic pigments. The lower side of such lichens is grey, dark-brown or black. At the first time, we evaluated photosynthetic activity distribution by chlorophyll fluorescence analysis on both lower and upper thallus sides for the foliose lichen Nephroma arcticum. We have demonstrated that photosynthesis proceeds not only on the green-colored upper side, but also on the gray lower side of the curled growing edges of the thallus lobes. These sides were differed in terms of PSII photochemical quantum yield, activity of non-regulatory dissipation and non-photochemical quenching of excited chlorophyll states (NPQ). Upper side was characterized by higher maximal PSII efficiency, whereas the lower one of the curled edges was characterized by higher actual photochemical quantum yield during actinic light acclimation. NPQ was higher on the upper surface, whereas, on the lower side (of the curled edges) non-regulatory dissipation was predominant. In terms of photosynthetic activity measurements, these results show, that actinic and measuring light reached the layer of phycobiont despite its shielding by mycobiont hyphae. On the melanized lower side in the basal thalline zone attached to the substratum photosynthesis was not detected. Lower side demonstrated higher level of light scattering in the reflectance spectra. We believe that different photoprotective mechanisms against high light are crucial on the upper and lower sides: NPQ on the upper surface, and light scattering and shielding by mycobiont on the lower side. Possible biological role of photosynthesis on the lower side is discussed.

Antimicrobial Compounds Isolated from Endolichenic Fungi: A Review

A lichen is a symbiotic relationship between a fungus and a photosynthetic organism, which is algae or cyanobacteria. Endolichenic fungi are a group of microfungi that resides asymptomatically within the thalli of lichens. Endolichenic fungi can be recognized as luxuriant metabolic artists that produce propitious bioactive secondary metabolites. More than any other time, there is a worldwide search for new antibiotics due to the alarming increase in microbial resistance against the currently available therapeutics. Even though a few antimicrobial compounds have been isolated from endolichenic fungi, most of them have moderate activities, implying the need for further structural optimizations. Recognizing this timely need and the significance of endolichenic fungi as a promising source of antimicrobial compounds, the activity, sources and the structures of 31 antibacterial compounds, 58 antifungal compounds, two antiviral compounds and one antiplasmodial (antimalarial) compound are summarized in this review. In addition, an overview of the common scaffolds and structural features leading to the corresponding antimicrobial properties is provided as an aid for future studies. The current challenges and major drawbacks of research related to endolichenic fungi and the remedies for them have been suggested.

The Fumarprotocetraric Acid Inhibits Tau Covalently, Avoiding Cytotoxicity of Aggregates in Cells

Neurodegenerative disorders, including Tauopathies that involve tau protein, base their pathological mechanism on forming proteinaceous aggregates, which has a deleterious effect on cells triggering an inflammatory response. Moreover, tau inhibitors can exert their mechanism of action through noncovalent and covalent interactions. Thus, Michael's addition appears as a feasible type of interaction involving an α, β unsaturated carbonyl moiety to avoid pathological confirmation and further cytotoxicity. Moreover, we isolated three compounds from Antarctic lichens Cladonia cariosa and Himantormia lugubris: protolichesterinic acid (1), fumarprotocetraric acid (2), and lichesterinic acid (3). The maleimide cysteine labeling assay showed that compounds 1, 2, and 3 inhibit at 50 µM, but compounds 2 and 3 are statistically significant. Based on its inhibition capacity, we decided to test compound 2 further. Thus, our results suggest that compound 2 remodel soluble oligomers and diminish β sheet content, as demonstrated through ThT experiments. Hence, we added externally treated oligomers with compound 2 to demonstrate that they are harmless in cell culture. First, the morphology of cells in the presence of aggregates does not suffer evident changes compared to the control. Additionally, the externally added aggregates do not provoke a substantial LDH release compared to the control, indicating that treated oligomers do not provoke membrane damage in cell culture compared with aggregates alone. Thus, in the present work, we demonstrated that Michael's acceptors found in lichens could serve as a scaffold to explore different mechanisms of action to turn tau aggregates into harmless species.

Lichens as a repository of bioactive compounds: an open window for green therapy against diverse cancers

Lichens, algae and fungi-based symbiotic associations, are sources of many important secondary metabolites, such as antibiotics, anti-inflammatory, antioxidants, and anticancer agents. Wide range of experiments based on in vivo and in vitro studies revealed that lichens are a rich treasure of anti-cancer compounds. Lichen extracts and isolated lichen compounds can interact with all biological entities currently identified to be responsible for tumor development. The critical ways to control the cancer development include induction of cell cycle arrests, blocking communication of growth factors, activation of anti-tumor immunity, inhibition of tumor-friendly inflammation, inhibition of tumor metastasis, and suppressing chromosome dysfunction. Also, lichen-based compounds induce the killing of cells by the process of apoptosis, autophagy, and necrosis, that inturn positively modulates metabolic networks of cells against uncontrolled cell division. Many lichen-based compounds have proven to possess potential anti-cancer activity against a wide range of cancer cells, either alone or in conjunction with other anti-cancer compounds. This review primarily emphasizes on an updated account of the repository of secondary metabolites reported in lichens. Besides, we discuss the anti-cancer potential and possible mechanism of the most frequently reported secondary metabolites derived from lichens.

Contribution of Cyanotoxins to the Ecotoxicological Role of Lichens

The fascinating world of lichens draws the attention of the researchers because of the numerous properties of lichens used traditionally and, in modern times, as a raw material for medicines and in the perfumery industry, for food and spices, for fodder, as dyes, and for other various purposes all over the world. However, lichens being widespread symbiotic entities between fungi and photosynthetic partners may acquire toxic features due to either the fungi, algae, or cyano-procaryotes producing toxins. By this way, several common lichens acquire toxic features. In this survey, recent data about the ecology, phytogenetics, and biology of some lichens with respect to the associated toxin-producing cyanoprokaryotes in different habitats around the world are discussed. Special attention is paid to the common toxins, called microcystin and nodularin, produced mainly by the Nostoc species. The effective application of a series of modern research methods to approach the issue of lichen toxicity as contributed by the cyanophotobiont partner is emphasized.

The Under-explored Extracellular Proteome of Aero-Terrestrial Microalgae Provides Clues on Different Mechanisms of Desiccation Tolerance in Non-Model Organisms

Trebouxia sp. (TR9) and Coccomyxa simplex (Csol) are desiccation-tolerant lichen microalgae with different adaptive strategies in accordance with the prevailing conditions of their habitats. The remodelling of cell wall and extracellular polysaccharides depending on water availability are key elements in the tolerance to desiccation of both microalgae. Currently, there is no information about the extracellular proteins of these algae and other aero-terrestrial microalgae in response to limited water availability. To our knowledge, this is the first report on the proteins associated with the extracellular polymeric substances (EPS) of aero-terrestrial microalgae subjected to cyclic desiccation/rehydration. LC-MS/MS and bioinformatic analyses of the EPS-associated proteins in the two lichen microalgae submitted to four desiccation/rehydration cycles allowed the compilation of 111 and 121 identified proteins for TR9 and Csol, respectively. Both sets of EPS-associated proteins shared a variety of predicted biological functions but showed a constitutive expression in Csol and partially inducible in TR9. In both algae, the EPS-associated proteins included a number of proteins of unknown functions, some of which could be considered as small intrinsically disordered proteins related with desiccation-tolerant organisms. Differences in the composition and the expression pattern between the studied EPS-associated proteins would be oriented to preserve the biochemical and biophysical properties of the extracellular structures under the different conditions of water availability in which each alga thrives.

Apparent electron transport rate - a non-invasive proxy of photosynthetic CO2 uptake in lichens

During desiccation, both apparent electron transport rate (ETR_app) and photosynthetic CO₂ uptake peak when external water has evaporated. External water, causing suprasaturation, weakens the strong correlation between ETR_app and CO₂ uptake. Lichens are poikilohydric organisms passively regulated by ambient conditions. In theory, apparent electron transport rate (ETR_app), estimated by photosystem II yield measured in light (Φ_PSII), is a proxy of photosynthetic CO₂ uptake. Hydration level, however, is a complicating factor, particularly during suprasaturation that strongly reduces CO₂ diffusion. Here, the cephalolichen Lobaria pulmonaria and two chlorolichens Parmelia sulcata and Xanthoria aureola were excessively hydrated before photosynthetic CO₂ uptake and Φ_PSII using imaging fluorescence tools were simultaneously measured while drying at 200 µmol photons m^-2 s^-1. CO₂ uptake peaked when hydration had declined to a level equivalent to their respective internal water holding capacity (WHC_internal) i.e., the water per thallus area after blotting external water. CO₂ uptake and ETR_app in all species were highly correlated at hydration levels below WHC_internal, but weaker at higher hydration (chlorolichens) or absent (cephalolichen). Yet, at a specimen level for the two chlorolichens, the correlation was strong during suprasaturation. The CO₂ uptake-ETR_app relationship did not differ between measured species, but may vary between other lichens because the slope depends on cortical transmittance and fraction of electrons not used for CO₂ uptake. For new lichen species, calibration of ETR_app against CO₂ uptake is therefore necessary. At intrathalline scales, Φ_PSII during drying initially increased along thallus margins before reaching maximum values in central portions when hydration approached WHC_internal. WHC_internal represents the optimal hydration level for lichen photosynthesis. In conclusion, ETR_app is an easily measured and reliable proxy of CO₂ uptake in thalli without external water but overestimates photosynthesis during suprasaturation.

Chlorophyll a fluorescence and Raman spectroscopy can monitor activation/deactivation of photosynthesis and carotenoids in Antarctic lichens

Lichens survive harsh weather of Antarctica as well as of other hostile environments worldwide. Therefore, this investigation is important to understand the evolution of life on Earth in relation to their stress tolerance strategy. We have used chlorophyll a fluorescence (ChlF) and Raman spectroscopy, respectively, to monitor the activation/deactivation of photosynthesis and carotenoids in three diverse Antarctic lichens, Dermatocarpon polyphyllizum (DP), Umbilicaria antarctica (UA), and Leptogium puberulum (LP). These lichens, post 4 h or 24 h of hydration, showed differences in their ChlF transients and values of major ChlF parameters, e.g., in the maximum quantum efficiency of PSII photochemistry (F_v/F_m), and yields of fluorescence and heat dissipation (Φ_f,d), of effective quantum efficiency of PSII photochemistry (Φ_PSII) and of non-photochemical quenching (Φ_npq), which may be due to quantitative and/or qualitative differences in the composition of their photobionts. For understanding the kinetics of hydration-induced activation of photosynthesis, we screened Φ_PSII of these lichens and reported its non-linear stimulation on a minute time scale; half of the activation time (t_1/2) was fastest ~4.05 ± 0.29 min for DP, which was followed by 5.46 ± 0.18 min for UA, and 13.95 ± 1.24 min for LP. Upon drying of fully activated lichen thallus, there was a slow decay, in hours, of relative water content (RWC) as well as of F_v/F_m. Raman spectral signatures were different for lichens having algal (in DP and UA) and cyanobacteria (in LP) photobionts, and there was a significant shift in ν₁(C=C) Raman band of carotenoids post 24 h hydration as compared to their value at a dry state or post 4 h of hydration; this shift was decreased, when drying, in DP and LP but not in UA. We conclude that hydration nonlinearly activated photosynthetic apparatus/reactions of these lichens in minute time range but there was a de-novo synthesis of chlorophylls as well as of carotenoids post 24 h. Their dehydration-induced deactivation, however, was comparatively slow, in hours range, and there seemed a degradation of synthesized chlorophylls and carotenoids post dryness. We conclude that in extremophilic lichens, their photosynthetic partners, in particular, possess a complex survival and photoprotective strategy to be successful in the extreme terrestrial environments in Antarctica.

Disentangling sources of trace element air pollution in complex urban areas by lichen biomonitoring. A case study in Milan (Italy)

In this study we investigated the bioaccumulation of selected trace elements in lichen samples transplanted for three months in Milan, Italy, with the aim of assessing the main environmental contaminants and the overall pollution load, and of disentangling the main air pollution sources as well as of estimating fluxes of element deposition. The results highlighted Cu and Sb as important contaminants and suggested a common origin for these two elements from railways and non-exhaust sources of vehicular traffic such as brake abrasion. High or very high global air pollution emerged for all study sites. Source apportionment outlined three main factors, that found reliable correlation with distance from major roads and railways, an industrial plant, and soil resuspension. Ranges of estimated mean annual element deposition rates in the study area were similar to those reported for other cities.

The macroevolutionary dynamics of symbiotic and phenotypic diversification in lichens

Symbioses are evolutionarily pervasive and play fundamental roles in structuring ecosystems, yet our understanding of their macroevolutionary origins, persistence, and consequences is incomplete. We traced the macroevolutionary history of symbiotic and phenotypic diversification in an iconic symbiosis, lichens. By inferring the most comprehensive time-scaled phylogeny of lichen-forming fungi (LFF) to date (over 3,300 species), we identified shifts among symbiont classes that broadly coincided with the convergent evolution of phylogenetically or functionally similar associations in diverse lineages (plants, fungi, bacteria). While a relatively recent loss of lichenization in Lecanoromycetes was previously identified, our work instead suggests lichenization was abandoned far earlier, interrupting what had previously been considered a direct switch between trebouxiophycean and trentepohlialean algal symbionts. Consequently, some of the most diverse clades of LFF are instead derived from nonlichenized ancestors and re-evolved lichenization with Trentepohliales algae, a clade that also facilitated lichenization in unrelated lineages of LFF. Furthermore, while symbiont identity and symbiotic phenotype influence the ecology and physiology of lichens, they are not correlated with rates of lineage birth and death, suggesting more complex dynamics underly lichen diversification. Finally, diversification patterns of LFF differed from those of wood-rotting and ectomycorrhizal taxa, likely reflecting contrasts in their fundamental biological properties. Together, our work provides a timeline for the ecological contributions of lichens, and reshapes our understanding of symbiotic persistence in a classic model of symbiosis.

Distribution patterns of arsenic species in a lichen biomonitor

As stand-alone approaches, chromatographic separations of arsenic in lichen using HPLC-ICP-MS or the use of sequential extractions have historically been shown to have low analyte recoveries and poor analyte selectivity respectively. This study modifies the first step of a sequential extraction with a chromatographic separation of five arsenic species using HPLC-ICP-MS, followed by a three-step sequential extraction and analysis with ICP-MS. The method was applied to lichens from a rural and urban site to demonstrate the applicability thereof, and the sum of arsenic concentrations from the extraction steps were compared to the total arsenic concentrations. Short term species stability of the As species in the lichen matrix was also evaluated over 1 month in the water-extractable fraction, where As species concentrations changed week by week, providing insight into biotransformation mechanisms. In the modified extraction step, dimethylarsinic acid (DMA) and arsenobetaine and an unknown As species (AsB + U1) were statistically (p < 0.05) higher in the urban site than the rural site. Analyte recoveries using the combined method were higher than other studies reported in literature, with percentage recoveries of 104% and 111% of As in the urban and rural sites respectively. Arsenic concentrations were found in the following order of abundance at both sites: oxidizable > reducible > water-extractable > residual. Concentrations of total As in the oxidizable and non-bioavailable fraction were statistically lower (p < 0.05) in the rural site than in the urban site. Based upon the information gained from this study, we could draw concise conclusions regarding the source apportionment, timing and the magnitude of the pollution event.

Endogenous NO Is Involved in Dissimilar Responses to Rehydration and Pb(NO3)2 in Ramalina farinacea Thalli and Its Isolated Phycobionts

Lichens undergo desiccation/rehydration cycles and are permeable to heavy metals, which induce free radicals. Nitrogen monoxide (NO) regulates important cellular functions, but the research on lichen NO is still very scarce. In Ramalina farinacea thalli, NO seems to be involved in the peroxidative damage caused by air pollution, antioxidant defence and regulation of lipid peroxidation and photosynthesis. Our hypothesis is that NO also has a critical role during the rehydration and in the responses to lead of its isolated phycobionts (Trebouxia sp. TR9 and Trebouxia jamesii). Therefore, we studied the intracellular reactive oxygen species (ROS) production, lipid peroxidation and chlorophyll autofluorescence during rehydration of thalli and isolated microalgae in the presence of a NO scavenger and Pb(NO₃)₂. During rehydration, NO scavenging modulates free radical release and chlorophyll autofluorescence but not lipid peroxidation in both thalli and phycobionts. Pb(NO₃)₂ reduced free radical release (hormetic effect) both in the whole thallus and in microalgae. However, only in TR9, the ROS production, chlorophyll autofluorescence and lipid peroxidation were dependent on NO. In conclusion, Pb hormetic effect seems to depend on NO solely in TR9, while is doubtful for T. jamesii and the whole thalli.

Symbiosis extended: exchange of photosynthetic O2 and fungal-respired CO2 mutually power metabolism of lichen symbionts

Lichens are a symbiosis between a fungus and one or more photosynthetic microorganisms that enables the symbionts to thrive in places and conditions they could not compete independently. Exchanges of water and sugars between the symbionts are the established mechanisms that support lichen symbiosis. Herein, we present a new linkage between algal photosynthesis and fungal respiration in lichen Flavoparmelia caperata that extends the physiological nature of symbiotic co-dependent metabolisms, mutually boosting energy conversion rates in both symbionts. Measurements of electron transport by oximetry show that photosynthetic O₂ is consumed internally by fungal respiration. At low light intensity, very low levels of O₂ are released, while photosynthetic electron transport from water oxidation is normal as shown by intrinsic chlorophyll variable fluorescence yield (period-4 oscillations in flash-induced Fv/Fm). The rate of algal O₂ production increases following consecutive series of illumination periods, at low and with limited saturation at high light intensities, in contrast to light saturation in free-living algae. We attribute this effect to arise from the availability of more CO₂ produced by fungal respiration of photosynthetically generated sugars. We conclude that the lichen symbionts are metabolically coupled by energy conversion through exchange of terminal electron donors and acceptors used in both photosynthesis and fungal respiration. Algal sugars and O₂ are consumed by the fungal symbiont, while fungal delivered CO₂ is consumed by the alga.

Presence and possible origin of positive Eu anomaly in shoot samples of Juncus effusus L

BACKGROUND

The rare earth elements (REE) are non-essential elements for plants. They stimulate plant growth at low doses, but at high levels are phytotoxic. There are differences in concentrations of REE in various organs of the same plant species, but the normalized REE patterns can be very similar in samples of the same species collected in different locations. Here we compare normalized REE curves in above-ground samples of Juncus effusus L. (common rush, soft rush) collected from sites with different land-use types.

METHODS

The concentrations of rare earth elements were measured in 55 shoot samples of J. effusus L. The samples were collected from 15 sampling sites located in the Holy Cross Mts., south-central Poland and analyzed with the use of inductively coupled plasma mass spectrometry (ICP-MS). The results were normalized to the North American Shale Composite and anomalies of different elements were calculated.

RESULTS

Total REE concentrations varied from 0.028 mg/kg to 2.7 mg/kg. The samples were enriched in the light REE (from La to Eu) with the highest concentrations of La and Ce. The North American Shale Composite (NASC)-normalized REE curves were roughly similar in all samples except for two samples collected in the acid mine drainageaffected areas.

CONCLUSION

All samples showed positive europium anomalies in NASC-normalized REE concentration patterns. The most probable explanation of this is that the uptake and translocation of Eu in J. effusus (and possibly in other wetland plants) is caused by a short-term decrease of the redox potential in a rhizosphere favoring reduction of Eu³⁺ to Eu²⁺ and thus enhancing Eu mobility in the soil-plant environment.

Effects of wet atmospheric nitrogen deposition on epiphytic lichens in the subtropical forests of Central China: Evaluation of the lichen food supply and quality of two endangered primates

Over the last few decades, the threat posed to biodiversity and ecosystem function by atmospheric nitrogen (N) deposition has been increasingly recognized. The disturbed nutrient balance and species composition of plants induced by higher N deposition can impact the biodiversity of the organisms that consume the plants. In this research, we implemented several experiments to estimate the effects of increased N deposition on the growth, survival, and nutrients of the dominant epiphytic lichens in the subtropical mountains in Central China to assess the lichen food amount and nutritional quality for two endangered primates endemic to China. Our results indicated that the thallus growth and propagule survival of the lichens were significantly decreased when nitrogen addition changed from 6.25 to 50.0 kg N·ha^-1·y^-1; it was also shown that lichen biomass could be decreased by 11.2%-70.2% when the deposition addition exceeded 6.25 kg N·ha^-1·y^-1. Further, our study revealed that increased nitrogen deposition also reduced the nutritional quality of the lichens via reducing the soluble protein and soluble sugar levels and increasing the fiber content, which would substantially affect the diet selection of the plants consumers in the region, particularly the populations of the two lichen-eating endangered primate species, Rhinopithecus roxellana and R. bieti. Our experimental study suggested that the nitrogen pollution derived from anthropogenic activities could cause cascading effects for the whole forest ecosystem of Central China; thus, more studies about nitrogen deposition in this region are required.

Cladonia uncialis as a valuable raw material of biosynthetic compounds against clinical strains of bacteria and fungi

Cladonia uncialis is a lichen species with confirmed antibacterial activity and whose genome has been recently sequenced, enabling first attempts in its functional characterization. In this work, we investigated activity of the C. uncialis acetone extract (CUE) and usnic acid (UA) enantiomers against ten clinical microbial strains causing skin infections. The results showed that CUE, containing (-)-UA and squamatic acid, assayed at the same concentrations as UA, was noticeably more active than (-)-UA alone, in its pure form. The studied CUE displayed an activity that was comparable to that of (+)-UA observed for Staphylococcus epidermidis and Enterococcus faecium (18-24 mm zone of growth inhibition), but did not display any activity against fungal strains. The CUE demonstrated low cytotoxicity against HaCaT cells, in comparison to UA enantiomers, which is important for its therapeutic use. Results of the antioxidant assay (DPPH) indicated low antioxidant activity (IC50>200 µg/mL) of CUE, while the total phenolic content was 70.36 mg Gallic Acid Equivalent/g of the dry extract.

Photobiont-dependent humidity threshold for chlorolichen photosystem II activation

Photobiont type influences the relative humidity threshold at which photosystem II activates in green algal lichens. Water vapor uptake alone can activate photosynthesis in lichens with green algal photobionts. However, the minimum relative humidity needed for activation is insufficiently known. The objective of this study was to quantify the humidity threshold for photosystem II (PSII) activation in a range of chlorolichen species associated with photobionts from Trebouxiaceae, Coccomyxaceae and Trentepohliaceae. These lichens exhibit distribution, habitat and substrate patterns that are likely coupled to their efficiency in utilizing water vapor at lower levels of relative humidity (RH) for photosynthesis. Using chlorophyll fluorescence imaging during water uptake from humid air of 25 species of chlorolichens representing the above photobiont groups, we monitored PSII activation within controlled chambers with constant RH at five levels ranging from 75.6 to 95.4%. The results demonstrate clear photobiont-specific activation patterns: the trentepohlioid lichens activated PSII at significantly lower RH (75.6%) than trebouxioid (81.7%) and coccomyxoid (92.0%) lichens. These responses are consistent with a preference for warm and sheltered habitats for trentepohlioid lichens, with cool and moist habitats for the coccomyxoid lichens, and with a more widespread occurrence of the trebouxioid lichens. Within each photobiont group, lichen species exposed to marine aerosols in their source habitats seemed to be activated at lower RH than lichens sampled from inland sites. High osmolyte concentration may therefore play a role in lowering a photobiont's activation threshold. We conclude that photobiont type influences water vapor-driven photosynthetic activation of lichens, thereby shaping the ecological niches in which they occur.

A facile in vivo procedure to analyze metabolic pathways in intact lichens

Lichen secondary metabolites show important biological activities as well as pharmaceutical and chemotaxonomic potential. In order to utilize such substances of interest, detailed knowledge of their biosynthetic pathways is essential. ¹³ CO₂ -pulse/chase experiments using intact thalli of the lichen Usnea dasopoga resulted in multiple ¹³ C-labeled isotopologs in amino acids, but not in the dibenzofuran derivative usnic acid - one of the best-studied lichen metabolites, with considerable and renewed interest for pharmaceutical and lifestyle applications. Spraying an aqueous solution of [U-¹³ C₆ ]glucose onto the thalli of U. dasopoga afforded a specific mixture of multiple ¹³ C-labeled isotopologs in usnic acid. One- and two-dimensional NMR analysis of the crude lichen extract corroborated the polyketide biosynthetic pathway via methylphloroacetophenone but not via phloroacetophenone. With usnic acid as an exemplar, we provide proof-of-principle experiments that can be used in general to study metabolic pathways and fluxes in intact lichens.

Lichen Secondary Metabolite Physciosporin Decreases the Stemness Potential of Colorectal Cancer Cells

Secondary metabolites of lichens are promising bioresources for candidate anti-cancer drugs. Accordingly, several approaches have been proposed for screening these molecules for novel anti-cancer lead compounds. In this study, we found that a non-toxic concentration of physciosporin, a compound isolated from Pseudocyphellaria granulata, significantly decreased colony formation on soft agar and spheroid formation by CSC221 cancer stem-like cells. Physciosporin also decreased spheroid formation in other colorectal cancer cell lines, including DLD1, Caco2, and HT29. Aldehyde dehydrogenase-1 (ALDH1), the most important cancer stem marker, was sharply downregulated at both the protein and mRNA level following treatment with physciosporin. Physciosporin also decreased the transcriptional activity of the glioma-associated oncogene homolog zinc finger protein (Gli), as well as the Hes1 and CSL promoters, in reporter assays. Moreover, the drug significantly suppressed spheroid formation in CSC221 cells overexpressing Gli1/2 or EN1 (an S2-cleaved but membrane-tethered form of human Notch1) but did not suppress spheroid formation in cells overexpressing both Gli1/2 and ∆EN1, suggesting that physciosporin suppresses colon cancer cell stemness through the Sonic hedgehog and Notch signaling pathways. Together, these results demonstrate for the first time that physciosporin is a potent inhibitor of colorectal cancer cell stemness.

Lichen as a Biomonitor for Vehicular Emission of Metals: A Risk Assessment of Lichen Consumption by the Sichuan Snub-Nosed Monkey (Rhinopithecus roxellana)

Two lichen species, Usnea aciculifera and Usnea luridorufa, were used as biomonitors for the deposition of traffic-related metals in China's Shennongjia National Nature Reserve. The suitability of the two lichen species for use as biomonitors was compared. The health threat to the Sichuan snub-nosed (aka golden) monkey (Rhinopithecus roxellana) from consuming lichen with elevated metal concentrations due to vehicular traffic was then assessed. Lichens, with large surface areas and neither roots nor stomata, efficiently absorb both particulate and gaseous air pollutants. The resulting data was used to assess the effect of heavy metal accumulation on the lichens as well as the health risk imposed on the monkeys as lichen is a primary food source. Lichen samples were collected in the core area of the reserve at three locations of varying traffic intensity. A forth site in the reserve, with no proximate traffic, was used as the control. Results show: (1) lichen from high traffic sites has significantly higher concentrations of Fe, Cd, Pb Zn, and Cr than lichen collected from the control site; (2) vehicular traffic is the primary source of metals in lichen; (3) U. luridorufa collected at high traffic sites displayed decreased photosynthetic efficiency, an indication of stress; (4) intake of Cd and Pb from vehicle emissions in the Shennongjia National Nature Reserve could adversely affect snub-nosed monkey health. This research advances the science of biomonitoring, contributes to environmental protection efforts in China's nature reserves and helps improve food safety for Sichuan snub-nosed monkey, a national treasure of China.

Assessment of Pb2+ removal capacity of lichen (Evernia prunastri): application of adsorption kinetic, isotherm models, and thermodynamics

Biological materials play a significant role in the treatment of heavy metal-contaminated soil and wastewater. In this study, the Pb²⁺ biosorption potential of lichen Evernia prunastri, extensively available at a forest in Bilecik-Turkey, was investigated at batch-scale level. The optimal conditions were determined and the adsorption isotherms, kinetics, and thermodynamic calculations were also done. In order to have detailed knowledge about metal biosorption, SEM, FTIR, and BET analyses were carried out before and after the biosorption process. The optimal pH was found pH 4 and the maximum metal uptake capacity was found as 0.067 mol kg^-1. The results of this study indicate that the lichen was effectively applied to the removal of Pb²⁺ process as an inexpensive biosorbent from industrial wastewater.

Comparison of two noninvasive methods for measuring the pigment content in foliose macrolichens

Chlorophyll content in lichens is routinely used as an accurate indicator of lichen vigor, interspecific differences, and the effect of site-related environmental parameters. Traditional methods of chlorophyll extraction are destructive, time-consuming, expensive, and inoperable, especially when measuring large quantities of chlorophyll. However, non-destructive methods of measurement using portable chlorophyll meters are rarely used for lichens. Considering the characteristics of lichens such as rough blade surface and absence of chlorophyll b in cyanolichens, we compared the non-destructive methods with traditional methods and evaluated their applicability in studying lichen pigment content. Two instruments, SPAD-502 and CCM-300, were used to measure the pigment content of seven foliose lichen species. These pigment readings were compared with those determined using the dimethyl sulphoxide (DMSO) extraction method. Significant correlations were observed between SPAD/CCM values and pigments (chlorophyll and total carotenoids) extracted from chlorolichens, especially species with a smooth surface. The CCM-300 was more accurate in detecting the pigment content of foliose chlorolichens. However, both instruments showed certain limitations in the determination of pigment content in cyanolichens, especially gelatinous species. For example, CCM-300 often failed to give specific values for some cyanolichen samples, and both instruments showed low measurement accuracy for cyanolichens. Based on the high correlation observed between chlorophyll meter readings and pigments extracted from chlorolichens, equations obtained in this study enabled accurate prediction of pigment content in these lichens.

Tolerance to Cyclic Desiccation in Lichen Microalgae is Related to Habitat Preference and Involves Specific Priming of the Antioxidant System

Oxidative stress is a crucial challenge for lichens exposed to cyclic desiccation and rehydration (D/R). However, strategies to overcome this potential stress are still being unraveled. Therefore, the physiological performance and antioxidant mechanisms of two lichen microalgae, Trebouxia sp. (TR9) and Coccomyxa simplex (Csol), were analyzed. TR9 was isolated from Ramalina farinacea, a Mediterranean fruticose epiphytic lichen adapted to xeric habitats, while Csol is the phycobiont of Solorina saccata, a foliaceous lichen that grows on humid rock crevices. The tolerance to desiccation of both species was tested by subjecting them to different drying conditions and to four consecutive daily cycles of D/R. Our results show that a relative humidity close to that of their habitats was crucial to maintain the photosynthetic rates. Concerning antioxidant enzymes, in general, manganese superoxide dismutases (MnSODs) were induced after desiccation and decreased after rehydration. In TR9, catalase (CAT)-A increased, and its activity was maintained after four cycles of D/R. Ascorbate peroxidase activity was detected only in Csol, while glutathione reductase increased only in TR9. Transcript levels of antioxidant enzymes indicate that most isoforms of MnSOD and FeSOD were induced by desiccation and repressed after rehydration. CAT2 gene expression was also upregulated and maintained at higher levels even after four cycles of D/R in accordance with enzymatic activities. To our knowledge, this is the first study to include the complete set of the main antioxidant enzymes in desiccation-tolerant microalgae. The results highlight the species-specific induction of the antioxidant system during cyclic D/R, suggesting a priming of oxidative defence metabolism.

Integrity of lichen cell membranes as an indicator of heavy-metal pollution levels in soil

The epigeic lichens Cladonia rei and Diploschistes muscorum are effective heavy-metal-tolerant colonisers of highly polluted and disturbed sites. In this study we compare their bioaccumulation capacities, accumulation patterns, and responses to heavy-metal stress, as expressed in terms of cell membrane damage. We also aim at verifying the relationships between cell membrane damage and levels of soil pollution with heavy metals, and thereby to identify the bioindicative value of this physiological parameter. Total and intracellular concentrations of Zn, Pb, Cd, As, Cu, and Ni were measured in 140 samples of lichens and corresponding soil, collected from variously contaminated sites. Relative electrical conductivity (EC%) values were determined concurrently in the lichen samples. The studied lichens differ considerably in intracellular uptake susceptibility and the related reduction in membrane integrity. In C. rei thalli, more than half of Zn, Pb, Cd, and As loads are accumulated extracellularly, whereas D. muscorum exhibits a tendency towards intracellular accumulation of the same elements. This property is clearly reflected in cell membrane damage, which is considerably greater in the latter species irrespective of study site. This indicates that intracellular heavy-metal accumulation affects the level of cell membrane damage. Two soil pollution classes were distinguished for both lichens based on element contents in host-substrate samples. The losses of cell membrane integrity in lichen thalli are related to these classes. EC% values above 16 in C. rei and above 20 in D. muscorum suggest elevated levels of heavy metals in the soil. Consequently, this physiological parameter can serve as an early warning indicator for detection of elevated metal concentrations in soil. The biomonitoring method proposed here involves common and widespread lichen species and can be widely applied in post-industrial areas.

A new measurement tool to consider for airborne pollutants evaluations using lichens

An important factor affecting acquisition of pollution elements could be the lichen growth form. The Brunauer-Emmett-Teller theory approach has been used to determinate the specific area surface (BET-area) of solids by gas multilayer adsorption. Taking this standard method as a new tool, we measure the specific thallus area in foliose and fruticose lichens to evaluated area/volume relation for bioaccumulation prospects. Some preliminary results of elemental contents such as REEs (La, Sc, Sr) and pollutants (Cd, Co, Pb) were also measured to support the importance to use for the analysis of these thallus attributes.

Cytotoxic and Apoptotic Effects on Hepatocytes of Secondary Metabolites Obtained from Lichens

There are a large number of species of Antarctic lichens, and several studies describing the secondary metabolites present in these lichens, as well as the advances in understanding the chemistry of these metabolites, have been reported. In addition, some derivatives displaying interesting antibacterial effects have been described. The cytotoxic and apoptotic effects of 15 secondary metabolites (depsides, depsidones and usnic acid) obtained from Continental (Chilean) and Antarctic lichens were evaluated in primary cultures of rat hepatocytes. Intracellular lactate dehydrogenase release, caspase 3 activation and DNA fragmentation were measured. In this study, we have evaluated a set of markers associated with pivotal steps in the execution phase of apoptosis, in order to detect compounds with apoptotic effects on hepatocytes before significant necrosis takes place. Flow cytometric analysis of DNA fragmentation revealed an increase in apoptotic nuclei with sub-diploid DNA content after the exposure of hepatocytes to sub-cytotoxic concentrations of the compounds. Among these, salazinic acid, stictic acid and psoromic acid displayed significant apoptotic activities. Divaricatic acid showed only moderate apoptotic effects at sub-cytotoxic concentrations.

Background element content in the lichen Pseudevernia furfuracea: a comparative analysis of digestion methods

In bioaccumulation studies, the interpretation of pollutant contents in the target biomonitor has to be performed by assessing a deviation from an unaltered reference condition. A common strategy consists in the comparison with background element content (BEC) values, often built up by uncritically merging methodologically heterogeneous data. In this respect, the acid digestion of samples was identified as a major step affecting BEC data. Here, the analytical outcomes of two acid mixtures were compared on a set of matched paired samples of the lichen Pseudevernia furfuracea, a widely used biomonitor for which BEC values based on partial digestion were previously provided. The standard reference material BCR 482 (P. furfuracea) was used to validate analytical procedures consisting of either a HF total mineralization or an aqua regia partial one, both associated to ICP-MS multi-element analysis. In particular, the performance of the procedures was evaluated by comparing analytical results of field samples with the accuracy obtained on BCR aliquots (measured-to-expected percentage ratio). The total digestion showed a better performance for Al, As, Ba, Ca, Cd, Cu, Fe, Mn, Ni, Se, Sn, and Zn, whereas the opposite was found for Cr, Co, P, and S. Moreover, new BEC values were provided for P. furfuracea using a consolidated statistical approach, after a total sample digestion with hydrofluoric acid. The multivariate investigation of the background variability of 43 elements in 57 remote Italian sites led to the identification of geographically homogeneous areas for which BEC values are provided for use as reference in biomonitoring applications.

Temporal change of the accumulation of persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) in lichens in Switzerland between 1995 and 2014

The aim of this study was to assess the temporal change of atmospheric deposition patterns of persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) in Switzerland between 1995 and 2014 by a passive biomonitoring with lichens. Lichen tissues sampled at 16 representative sites in the same season of 1995 and 2014 were analyzed for a total of 94 individual and 27 sum parameters of POPs and PAHs by means of gas chromatography-mass spectrometry (GC/MS). The comparative analyses showed a decrease of 40 to 80% (medians) for most of the POPs and PAHs concentration in lichens at all site categories. Reduction in tissue concentration of the polychlorinated dibenzo-p-dioxins/furans (PCDD/PCDFs), such as the highly toxic 2,3,7,8-TetraCDD and the TEQ according to WHO (2005) were 66% and 73%, respectively. For the dioxin- and non-dioxin-like PCBs, a decrease of 67% and 58% was found. The average decrease of 30 organochlorine pesticides and insecticides (OCPs) was 65%, with a 94% decrease for lindane. For the 27 PAHs and for benzo(a)pyrene, an average decrease of 58% and 59% was found. Polybrominated diphenyl ethers (PBDE) showed reduced concentrations in lichens at rural and agglomeration sites, but an increase of contamination was observed at industrial and road traffic sites. The direct comparison of changes of POPs and PAHs concentrations in lichens and of emissions between 1995 and 2014 revealed consistent results. The results of this study highlight for the first time in biota the positive effect of emission regulation of POPs in Switzerland.

A correlative approach, combining chlorophyll a fluorescence, reflectance, and Raman spectroscopy, for monitoring hydration induced changes in Antarctic lichen Dermatocarpon polyphyllizum

Lichens are successful colonizers in extreme environments worldwide, and they are considered to have played an important role during the evolution of life. Here, we have used a correlative approach, combining three optical signals (chlorophyll a fluorescence (ChlF), reflectance, and Raman spectra), to monitor hydration induced changes in photosynthetic properties of an Antarctic chlorolichen Dermatocarpon polyphyllizum. We measured these three signals from this lichen at different stages (after 4 h, 24 h, and 48 h) of hydration, and compared the data obtained from this lichen in "dry state" as well as in different "hydrated state". We found that dry state of this lichen has: (1) no variable ChlF, (2) high reflectance, with no red-edge and almost zero photochemical reflectance index (PRI), and (3) low-intensity Raman bands of their carotenoids. Furthermore, 4 h of hydration, increased its relative water content (RWC) by 93%, showed red-edge in reflectance spectra, and changed the maximum quantum yield of PSII photochemistry (F_v/F_m) from 0 to 0.57 ± 0.01. We found that reflectance indices, normalized difference index (NDVI) and PRI, significantly differed between brown and black/green surface areas, at all hydration stages; whereas, a shift in the Raman ν₁(CC) band, between brown and black/green surface areas, occurred in 24 h or 48 h hydrated samples. These data indicate that hydration shortly (within 4 h) activated functions of photosynthetic apparatus, and the de novo synthesis of carotenoids occured in 24 h or 48 h. Furthermore, exposure to high irradiance (2000 μmol photons m^-2 s^-1), in 48 h hydrated lichen, significantly reduced F_v/F_m (signifies photoinhibition) and increased PRI (represents changes in xanthophyll pigments). We conclude that the implication of such a correlative approach is highly useful for understanding survival and protective mechanisms on extremophile photosynthetic organisms.

Effects of Biological Soil Crusts on Enzyme Activities and Microbial Community in Soils of an Arid Ecosystem

Arid ecosystems constitute 41% of land's surface and play an important role in global carbon cycle. In particular, biological soil crusts (BSC) are known to be a hotspot of carbon fixation as well as mineralization in arid ecosystems. However, little information is available on carbon decomposition and microbes in BSC and key controlling variables for microbial activities in arid ecosystems. The current study, carried out in South Mediterranean arid ecosystem, aimed to evaluate the effects of intact and removed cyanobacteria/lichen crusts on soil properties, soil enzyme activities, and microbial abundances (bacteria and fungi). We compared five different treatments (bare soil, soil with intact cyanobacteria, soil with cyanobacteria removed, soil with intact lichens, and soil with lichens removed) in four different soil layers (0-5, 5-10, 10-15, and 15-20 cm). Regardless of soil treatments, activities of hydrolases and water content increased with increasing soil depth. The presence of lichens increased significantly hydrolase activities, which appeared to be associated with greater organic matter, nitrogen, and water contents. However, phenol oxidase was mainly controlled by pH and oxygen availability. Neither fungal nor bacterial abundance exhibited a significant correlation with enzyme activities suggesting that soil enzyme activities are mainly controlled by edaphic and environmental conditions rather than source microbes. Interestingly, the presence of lichens reduced the abundance of bacteria of which mechanism is still to be investigated.

Tissue-specific localization of polyketide synthase and other associated genes in the lichen, Cladonia rangiferina, using laser microdissection

The biosynthesis of two polyketides, atranorin and fumarprotocetraric acid, produced from a lichen-forming fungus, Cladonia rangiferina (L.) F. H. Wigg. was correlated with the expression of eight fungal genes (CrPKS1, CrPKS3, CrPKS16, Catalase (CAT), Sugar Transporter (MFsug), Dioxygenase (YQE1), C₂H₂ Transcription factor (C₂H₂), Transcription Factor PacC (PacC), which are thought to be involved in polyketide biosynthesis, and one algal gene, NAD-dependent deacetylase sirtuin 2 (AsNAD)), using laser microdissection (LMD). The differential gene expression levels within the thallus tissue layers demonstrate that the most active region for potential polyketide biosynthesis within the lichen is the outer apical region proximal to the photobiont but some expression also occurs in reproductive tissue. This is the first study using laser microdissection to explore gene expression of these nine genes and their location of expression; it provides a proof-of-concept for future experiments exploring tissue-specific gene expression within lichens; and it highlights the utility of LMD for use in lichen systems.

Characterization of nitrogen deposition in a megalopolis by means of atmospheric biomonitors

An increase of nitrogen deposition resulting from human activities is not only a major threat for global biodiversity, but also for human health, especially in highly populated regions. It is thus important and in some instances legally mandated to monitor reactive nitrogen species in the atmosphere. The utilization of widely distributed biological species suitable for biomonitoring may be a good alternative. We assessed the suitability of an ensemble of atmospheric biomonitors of nitrogen deposition by means of an extensive sampling of a lichen, two mosses, and a bromeliad throughout the Valley of Mexico, whose population reaches 30 million, and subsequent measurements of nitrogen metabolism parameters. In all cases we found significant responses of nitrogen content, C:N ratio and the δ15N to season and site. In turn, the δ15N for the mosses responded linearly to the wet deposition. Also, the nitrogen content (R2 = 0.7), the C:N ratio (R2 = 0.6), and δ15N (R2 = 0.5) for the bromeliad had a linear response to NOx. However, the bromeliad was not found in sites with NOx concentrations exceeding 80 ppb, apparently of as a consequence of excess nitrogen. These biomonitors can be utilized in tandem to determine the status of atmospheric nitrogenous pollution in regions without monitoring networks for avoiding health problems for ecosystems and humans.

Survey of the occurrence of desiccation-induced quenching of basal fluorescence in 28 species of green microalgae

Desiccation-induced chlorophyll fluorescence quenching seems to be an indispensable part of desiccation resistance in the surveyed 28 green microalgal species. Lichens are desiccation tolerant meta-organisms. In the desiccated state photosynthesis is inhibited rendering the photobionts potentially sensitive to photoinhibition. As a photoprotective mechanism, strong non-radiative dissipation of absorbed light leading to quenching of chlorophyll fluorescence has been proposed. Desiccation-induced quenching affects not only variable fluorescence, but also the so-called basal fluorescence, F₀. This phenomenon is well-known for intact lichens and some free living aero-terrestrial algae, but it was often absent in isolated lichen algae. Therefore, a thorough screening for the appearance of desiccation-induced quenching was undertaken with 13 different aero-terrestrial microalgal species and lichen photobionts. They were compared with 15 aquatic green microalgal species, among them also three marine species. We asked the following questions: Do isolated lichen algae show desiccation-induced quenching? Are aero-terrestrial algae different in this respect to aquatic algae and is the potential for desiccation-induced quenching coupled to desiccation tolerance? How variable is desiccation-induced quenching among species? Most of the aero-terrestrial algae, including all lichen photobionts, showed desiccation-induced quenching, although highly variable in extent, whereas most of the aquatic algae did not. All algae displaying quenching were also desiccation tolerant, whereas all algae unable to perform desiccation-induced quenching were desiccation intolerant. Desiccation-induced fluorescence quenching seems to be an indispensable part of desiccation resistance in the investigated species.

Effect of UV-B radiation on the content of UV-B absorbing compounds and photosynthetic parameters in Parmotrema austrosinense from two contrasting habitats

We studied the resistance of Parmotrema austrosinense to UV-B stress. We focused on the effects of a high dose UV-B radiation on the content of chlorophylls, carotenoids and UV-B screening compounds. Photosynthetic parameters were measured by chlorophyll fluorescence (potential and effective quantum yields, photochemical and non-photochemical quenching) and evaluated in control and UV-B-treated lichens. Lichens from two different locations in Cordoba, Argentina, were selected: (i) high altitude and dry plots at (Los Gigantes) and (ii) lowland high salinity plots (Salinas Grandes). UV-B treatment led to a decrease in the content of photosynthetic pigments and UV-B screens (absorbance decrease in 220-350 nm) in the samples from Salinas Grandes, while in Los Gigantes samples, an increase in UV-B screen content was observed. Chlorophyll fluorescence parameters showed a UV-B-induced decline in F_V /F_M , Φ_PSII and qP indicating limitation of primary photosynthetic processes in photosystem II (PSII) of symbiotic alga, more pronounced in Salinas Grandes samples. Protective mechanism of PSII were activated by the UV-B treatment to a higher extent in samples from Salinas Grandes (NPQ 0.48) than in Los Gigantes samples (NPQ 0.26). We concluded that site-related characteristics, and in particular different UV-B radiation regimen, had a strong effect on resistance of the photosynthetic apparatus of P. austrosinense to UV-B radiation.

Relation between water status and desiccation-affected genes in the lichen photobiont Trebouxia gelatinosa

The relation between water status and expression profiles of desiccation -related genes has been studied in the desiccation tolerant (DT) aeroterrestrial green microalga Trebouxia gelatinosa, a common lichen photobiont. Algal colonies were desiccated in controlled conditions and during desiccation water content (WC) and water potential (Ψ) were measured to find the turgor loss point (Ψ_tlp). Quantitative real-time PCR was performed to measure the expression of ten genes related to photosynthesis, antioxidant defense, expansins, heat shock proteins (HSPs), and desiccation related proteins in algal colonies collected during desiccation when still at full turgor (WC > 6 g H₂O g^-1 dry weight), immediately before and after Ψ_tlp (-4 MPa; WC ∼ 1 g H₂O g^-1 dry weight) and before and after complete desiccation (WC < 0.01 g H₂O g^-1 dry weight), quantifying the HSP70 protein levels by immunodetection. Our analysis showed that the expression of eight out of ten genes changed immediately before and after Ψ_tlp. Interestingly, the expression of five out of ten genes changed also before complete desiccation, i.e. between 0.2 and 0.01 g H₂O g^-1 dry weight. However, the HSP70 protein levels were not affected by changes in water status. The study provides new evidences of the link between the loss of turgor and the expression of genes related to the desiccation tolerance of T. gelatinosa, suggesting the former as a signal triggering inducible mechanisms.

Metal-induced oxidative stress in terrestrial macrolichens

Short-term (24 h) responses of Cladonia arbuscula subsp. mitis and Cladonia furcata to copper (CuII) or chromium (CrIII) excess (10 or 100 μM) were compared. C. arbuscula accumulated more Cu and Cr at higher metal doses but both species revealed depletion of K and/or Ca amount. Not only Cu but also Cr typically elevated reactive oxygen species (ROS) formation (fluorescence microscopy detection of total ROS and hydrogen peroxide) and depleted nitric oxide (NO) signal, with Cu showing more negative impact on lipid peroxidation (BODIPY 581/591 C11 staining reagent). Metals and staining reagents also affected anatomical responses and photobiont/mycobiont visibility. Principally different impact of Cu and Cr was observed at antioxidative metabolites level, indicating various ways of metal-induced ROS removal and/or metal chelation: Cu strongly depleted glutathione (GSH) and stimulated phytochelatin 2 (PC2) content while ascorbic acid accumulation was depleted by Cu and stimulated by Cr. Subsequent experiment with GSH biosynthetic inhibitor (buthionine sulfoximine, BSO) revealed that 48 h of exposure is needed to deplete GSH and BSO-induced depletion of GSH and PC2 amounts under Cu or Cr excess elevated ROS but depleted NO. These data suggest close relations between thiols, NO and appearance of oxidative stress (ROS generation) under metallic stress also in lichens.