Photobiont Species Research Articles

Diversity of lichen mycobionts and photobionts and their relationships in the Ny-Ålesund region (Svalbard, High Arctic).

Lichens are dual organisms, with one major mycobiont and one major photobiont in each lichen symbiosis, which can survive extreme environmental conditions in the Arctic. However, the diversity and distribution of lichen photobionts in the Arctic remain poorly understood compared to their mycobiont partners. This study explored the diversity of lichen mycobionts and photobionts in 197 lichen samples collected from the Ny-Ålesund region (Svalbard, High Arctic). The nuclear ribosomal internal transcribed spacer (ITS) regions were sequenced and phylogenetic analyses were performed. The relationships between mycobionts and photobionts, as well as the association patterns, were also investigated. A total of 48 species of lichen mycobionts (16 families, nine orders) and 31 species/lineages of photobionts were identified. These 31 photobiont species belonged to one class (Trebouxiophyceae) and five genera, including 22 species of Trebouxia, five species of Asterochloris, two species of Chloroidium, one species of Symbiochloris, and one species of Coccomyxa. The results indicated that most analyzed lichen mycobionts could associate with multiple photobiont species, and the photobionts also exhibited a similar pattern. The results provided an important reference dataset for characterizing the diversity of lichen mycobionts and photobionts in the High Arctic region.

New lineages of photobionts in Bolivian lichens expand our knowledge on habitat preferences and distribution of Asterochloris algae

We studied the biodiversity of Asterochloris photobionts found in Bolivian lichens to better understand their global spatial distribution and adaptation strategies in the context of a worldwide phylogeny of the genus. Based on nuclear ITS rDNA, the chloroplast rbcL gene and the actin type I gene we reconstructed a phylogenetic tree that recovered nine new Asterochloris lineages, while 32 Bolivian photobiont samples were assigned to 12 previously recognized Asterochloris lineages. We also show that some previously discovered Asterochloris photobiont species and lineages may occur in a broader spectrum of climatic conditions, and mycobiont species and photobionts may show different preferences along an altitude gradient. To reveal general patterns of of mycobiont specificity towards the photobiont in Asterochloris, we tested the influence of climate, altitude, geographical distance and effects of symbiotic partner (mycobiont) at the species level of three genera of lichen forming fungi: Stereocaulon, Cladonia and Lepraria. Further, we compared the specificity of mycobionts towards Asterochloris photobionts in cosmopolitan, Neotropical, and Pantropical lichen forming fungi. Interestingly, cosmopolitan species showed the lowest specificity to their photobionts, but also the lowest haplotype diversity. Neotropical and Paleotropical mycobionts, however, were more specific.

Species diversity and photobiont localization specificities in epigene lichens (on the example of the genus <i>Cladonia</i>)

The article describes the taxonomic composition and photobionts localization specificities in above-ground lichens of the genus Cladonia. Moreover it analyzes the amount and algal species in thallus homogenates due to their age: in zones of active growth, aging zone and destruction zone; alga cells in washings from surface of thalli. Also the article analyzes the influence of the mycobiont on the photobiont species and abundance of the photobiont. It gives the comparison analysis of these data in lichens in the north taiga zone (Murmansk Region) and steppe zone (on the example of Orenburg Region). The method of direct microscopy helped to determine the taxonomic affiliation of the photobionts to the genus. Here the authors mean the size, shape of the cells, the nature of the chromatophore, etc. The number of photobionts in samples was studied both by light microscopy and fluorescence microscopy. The paper presents the comparison results of the amount and algae diversity in in the thalli of the above-ground lichens of the genus Cladonia due to their geographical location and the specificity of the age dynamics of the podecium. The research shows the fact that Asterochloris alga was the dominant group in the actively growing lichen podecia. However geographical location is not important. Chlorella, Stichococcus, Pseudococcomyxa were found in lichens algae. The authors believe that the new information about the changes in the taxonomic composition of algae, due to the age of the thallus is important for science. Pseudococcomyxa algae dominated in the old parts of the north taiga lichens and Stichococcus dominated in the steppe areas. Moreover the authors give the attempt of resynthesize lichen tallium from previously isolated cultures of the mycobiotic and photobiont. This attempt was unsuccessful at the period of the research work.

Cryptic diversity and symbiont interactions in rock-posy lichens

Identifying factors that influence species interactions is central to research in symbiotic systems. While lichens represent iconic models of symbiosis and play important roles in understanding the biology of symbiotic interactions, patterns of interactions in lichen symbionts and mechanisms governing these relationships are not well characterized. This is due, in part to the fact that current taxonomic approaches for recognizing diversity in lichen symbionts commonly fail to accurately reflect actual species diversity. In this study, we employed DNA-based approaches to circumscribed candidate species-level lineages in rock-posy lichen symbionts (mycobiont=Rhizoplaca s. lat. species; photobiont=Trebouxia species). Our results revealed a high degree of cryptic diversity in both the myco- and photobionts in these lichens. Using the candidate species circumscribed here, we investigated the specificity of the symbionts toward their partners and inferred the relative importance of various factors influencing symbiont interactions. Distinct mycobiont species complexes, ecozones, and biomes are significantly correlated with the occurrence of photobiont OTUs, indicating that complex interactions among mycobiont lineages, ecogeography, and microhabitat determine interactions between photobionts and their mycobionts in lichen symbiosis. One-to-one specificity between mycobiont and photobiont species was not found, with the exception of R. maheui that associated with a single Trebouxia OTU that was not found with other Rhizoplaca s. lat. species. We estimated the most recent common ancestor of the core Rhizoplaca group at c. 62.5Ma, similar in age to the diverse parmelioid core group in the well-studied family Parmeliaceae. However, in contrast to Parmeliaceae, species in Rhizoplaca were found to associate with a narrow range of photobionts. Our study provides important perspectives into species diversity and interactions in iconic lichen symbiotic systems and establishes a valuable framework for continuing research into rock-posy lichens.

Algal and fungal diversity in Antarctic lichens.

The composition of lichen ecosystems except mycobiont and photobiont has not been evaluated intensively. In addition, recent studies to identify algal genotypes have raised questions about the specific relationship between mycobiont and photobiont. In the current study, we analyzed algal and fungal community structures in lichen species from King George Island, Antarctica, by pyrosequencing of eukaryotic large subunit (LSU) and algal internal transcribed spacer (ITS) domains of the nuclear rRNA gene. The sequencing results of LSU and ITS regions indicated that each lichen thallus contained diverse algal species. The major algal operational taxonomic unit (OTU) defined at a 99% similarity cutoff of LSU sequences accounted for 78.7-100% of the total algal community in each sample. In several cases, the major OTUs defined by LSU sequences were represented by two closely related OTUs defined by 98% sequence similarity of ITS domain. The results of LSU sequences indicated that lichen-associated fungi belonged to the Arthoniomycetes, Eurotiomycetes, Lecanoromycetes, Leotiomycetes, and Sordariomycetes of the Ascomycota, and Tremellomycetes and Cystobasidiomycetes of the Basidiomycota. The composition of major photobiont species and lichen-associated fungal community were mostly related to the mycobiont species. The contribution of growth forms or substrates on composition of photobiont and lichen-associated fungi was not evident.

Photobiont selectivity for lichens and evidence for a possible glacial refugium in the Ross Sea Region, Antarctica

Lichens are a symbiosis consisting of heterotrophic, fungal (mycobiont) and photosynthetic algal or cyanobacterial (photobiont) components. We examined photobiont sequences from lichens in the Ross Sea Region of Antarctica using the internal transcribed spacer region of ribosomal DNA and tested the hypothesis that lichens from this extreme environment would demonstrate low selectivity in their choice of photobionts. Sequence data from three targeted lichen species (Buellia frigida, Umbilicaria aprina and Umbilicaria decussata) showed that all three were associated with a common algal haplotype (an unnamed Trebouxia species) which was present in all taxa and at all sites, suggesting lower selectivity. However, there was also association with unique, local photobionts as well as evidence for species-specific selection. For example, the cosmopolitan U. decussata was associated with two photobiont species, Trebouxia jamesii and an unnamed species. The most commonly collected lichen (B. frigida) had its highest photobiont haplotype diversity in the Dry Valley region, which may have served as a refugium during glacial periods. We conclude that even in these extreme environments, photobiont selectivity still has an influence on the successful colonisation of lichens. However, the level of selectivity is variable among species and may be related to the ability of some (e.g. B. frigida) to colonise a wider range of habitats.

Photobiont Relationships and Phylogenetic History of Dermatocarpon luridum var. luridum and Related Dermatocarpon Species.

Members of the genus Dermatocarpon are widespread throughout the Northern Hemisphere along the edge of lakes, rivers and streams, and are subject to abiotic conditions reflecting both aquatic and terrestrial environments. Little is known about the evolutionary relationships within the genus and between continents. Investigation of the photobiont(s) associated with sub-aquatic and terrestrial Dermatocarpon species may reveal habitat requirements of the photobiont and the ability for fungal species to share the same photobiont species under different habitat conditions. The focus of our study was todetermine the relationship between Canadian and Austrian Dermatocarpon luridum var. luridum along with three additional sub-aquatic Dermatocarpon species, and to determine the species of photobionts that associate with D. luridum var. luridum. Culture experiments were performed to identify the photobionts. In addition, the question of the algal sharing potential regarding different species of Dermatocarpon was addressed. Specimens were collected from four lakes in northwestern Manitoba, Canada and three streams in Austria. Three Canadian and four Austrian thalli of D. luridum var. luridum were selected for algal culturing. The nuclear Internal Transcribed Spacer (ITS) rDNA gene of the fungal partner along with the algal ITS rDNA gene was sequenced to confirm the identity of the lichen/photobiont and afterwards the same data sets were used in phylogenetic analyses to assess algal sharing. The green algal photobiont was identified as Diplosphaera chodatii (Trebouxiophyceae). The phylogenetic analyses of Canadian and Austrian D. luridum var. luridum revealed that ITS sequences are identical despite the vast geographic distance. Phylogenetic placement of D. luridum var. decipiens and D. arnoldianum suggested that a re-examination of the species status might be necessary. This study concluded that additional photobiont culture experiments should be conducted to answer the question of whether multiple photobionts are present within the genus Dermatocarpon.

Genetic diversity of photobionts in Antarctic lecideoid lichens from an ecological view point

AbstractAs part of a comprehensive study on lecideoid lichens in Antarctica, we investigated the photobiont diversity and abundance in 119 specimens of lecideoid lichens from 11 localities in the continental and maritime Antarctic. A phylogeny of these photobiont ITS sequences, including samples from arctic, alpine and temperate lowland regions, reveals the presence of five majorTrebouxiaclades in Antarctic lecideoid lichens. Two clades are formed by members of theT. jamesiiandT. impressaaggregates but for all other clades no close match to any knownTrebouxiaspecies could be found in sequence databases. One genetically uniform and well-supportedTrebouxiaclade was found only in the climatically unique cold desert regions of the Antarctic (preliminarily calledTrebouxiasp.URa1), where it is preferentially associated with the highly adapted Antarctic endemic lichenLecidea cancriformis. Levels of genetic photobiont diversity differ slightly, but insignificantly among ecological regions of the Antarctic and do not decrease towards regions with more unfavourable ecological conditions. The genetic diversity of photobionts varies among mycobiont species. Most pairwise comparisons reveal that these differences are insignificant, probably due to the small sample size for most species. The Antarctic lichens studied here are predominantly not specific for a single photobiont species or lineage, except forLecidella greeniiandL. siplei. These two species are preferably associated withTrebouxiasp. URa2, although in the sampling areas of both species, a pool of several other photobionts is available.Lecidea cancriformisassociates with the highest diversity of photobionts followed byL. andersonii.

Lichen myco- and photobiont diversity and their relationships at the edge of life (McMurdo Dry Valleys, Antarctica)

Lichen-forming fungi are among the most diverse group of organisms in Antarctica. Being poikilohydric, lichens are able to cope with harsh environmental conditions that exclude other organisms like vascular plants. The McMurdo Dry Valleys (Victoria Land, Continental Antarctica) are a hyperarid cold desert where macroscopic life is reduced to a few lichens and bryophyte species. We investigated the diversity of lichen-forming fungi and their associated photobionts in three valleys (Garwood, Marshall, and Miers). Correct identification of lichen-forming fungi from extreme ecosystems is complicated by the presence of numerous sterile and extremely modified thalli. To overcome this problem, we used a combined approach for the identification of the species present in the area, the first involving identification by means of standard characters and the second, two DNA-based (ITS region) species delimitation methods (General Mixed Yule-Coalescent model and genetic distances). In addition, we also used ITS sequences for the identification of the photobionts associated with the mycobionts. We studied the relationships between both bionts and assessed the degree of selectivity and specificity found in those associations. We also looked for landscape level spatial patterns in these associations. The two DNA-based methods performed quite differently, but 27 species of lichen-forming fungi and five putative species of photobionts were found in the studied area. Although there was a general trend for low selectivity in the relationships, high specificity was found in some associations and differential selectivity was observed in some lichen-forming fungi. No spatial structure was detected in the distribution of photobionts in the studied area.

Photobiont selectivity and specificity in Caloplaca species in a fog-induced community in the Atacama Desert, northern Chile

Little is known about the nature of the association between mycobionts and photobionts in isolated lichen communities. Here we studied the photobiont diversity of different Caloplaca species in a fog-induced community in the Atacama Desert. We compared nrDNA ITS sequences of both symbionts, photobionts and mycobionts, along with morphological characters of the different lichen thalli, to investigate the diversity and to assess the degree of selectivity and specificity of photobiont species in a community of Caloplaca species. Specimens of six fungal species (C. orthoclada, C. fernandeziana, and four undescribed species) were sampled along an altitudinal gradient on a coastal bluff with a strong fog presence, 60km south of Iquique, Chile. The photobiont species in this community belong to three species of the genus Trebouxia in the strict sense: T. arboricola, T. decolorans, and T. gigantea. Most of the fungal species were lichenized with photobionts belonging to different haplotypes of T. arboricola and T. decolorans, although the algae of three specimens, associated with two fungal species (C. orthoclada and C. sp1), were related to representatives of T. gigantea. These results indicate that members of the genus Caloplaca in northern Chile have moderate photobiont selectivity and appear to be selective to members of the T. arboricola group. Also, at high altitudes, changes in the photobiontal haplotype composition were observed in comparison to lower altitudes, probably generated by a higher water availability given higher fog condensation and precipitation in the upper areas of the bluff. This may suggest that ecological factors, such as altitude and water availability could result in a local shift of the associated photobiont and specialization as a product of local adaptation.

Identity and genetic structure of the photobiont of the epiphytic lichen Ramalina menziesii on three oak species in southern California

Lichens, a classic example of an obligate symbiosis between fungi and photobionts (which could be algae or cyanobacteria), are abundant in many terrestrial ecosystems. The genetic structure of the photobiont population found in association with a lichen-forming fungal species could be affected by fungal reproductive mode and by the spatial extent of gene flow in the photobiont. Using DNA sequences from one nuclear ribosomal and two chloroplast loci, we analyzed the genetic structure of the photobiont associated with the fungus Ramalina menziesii at an oak woodland study site in southern California. We had previously shown that the fungus exhibited no genetic structure among four local sites or three phorophyte species. Our goals were to identify the photobiont species and assess its genetic structure. We found that R. menziesii was highly specific in its photobiont choice and associated with one alga, Trebouxia decolorans. In contrast to the fungal population, we found significant differentiation among the algae sampled on three oak species and little genetic structure among the sites for two of the three algal loci. We hypothesize that R. menziesii is locally adapted to the phorophyte species through habitat specialization in the algal partner of the symbiosis.

Life history strategy ofLepraria borealisat an Antarctic inland site, Coal Nunatak

AbstractCoal Nunatak is an ice-free inland nunatak located on southern Alexander Island, adjacent to the west coast of the Antarctic Peninsula. Situated close to the Antarctic continent, it is characterized by harsh environmental conditions. Macroscopic colonization is restricted to micro-niches offering suitable conditions for a small number of lichens and mosses. The extreme environmental conditions place particular pressures on colonizers.Lepraria borealisis the dominant crustose lichen species present on Coal Nunatak, and shows distinctive features in its life history strategy, in particular expressing unusually low selectivity of the mycobiont towards potential photobionts. To assess selectivity, we measured algal DNA sequence polymorphism in a region of 480–660 bp of the nuclear internal transcribed spacer region of ribosomal DNA. We identified three different photobiont species, belonging to two different genera. We interpret this strategy as being advantageous in facilitating the colonization and community dominance ofL. borealisunder the isolation and extreme environmental conditions of Coal Nunatak.

Photobiont flexibility in the lichen Protoparmeliopsis muralis as revealed by ITS rDNA analyses

The genetic diversity of photobionts in the lichen Protoparmeliopsis muralis was examined to determine the identity of the photobiont and the level of selectivity for the photobiont by the mycobiont. Forty ITS rDNA sequences of photobionts from thirty nine specimens of Protoparmeliopsis muralis have been determined. The photobiont species were identified both by direct comparison with the available sequences and by phylogenetic analysis. The sequences obtained from P. muralis specimens belonged to different Trebouxia clades. The most common photobionts were T. incrustata and an unidentified lineage, here named as “muralis I”. Less common photobionts were T. asymmetrica and T. gigantea. Two unidentified Trebouxia spp. and a photobiont that belonged to the clade that includes T. impressa, T. flava and T. potteri were also found to be associated with P. muralis. Such flexibility has not been reported to date. Moreover, two different photobionts were found in a single specimen. They belonged to the T. gigantea clade and “muralis I” lineage. The low level of selectivity with respect to the photobiont may constitute an important aspect in that Protoparmeliopsis muralis is one of the most successful urban lichens in the world.

Lead and copper effects on lipid metabolism in cultured lichen photobionts with different phosphorus status

We evaluated the ability of heavy metals (copper, lead) to alter lipid metabolism in four algal lichen photobionts following short term exposure. Metal concentrations (10 μM) were equivalent to environmentally relevant levels that have been reported to have effects on intact algae. The algae were grown under normal or deficient phosphate conditions to assess any interactions with the heavy metal stress. Given the frequent sensitivity of lichens to copper and lead, there were surprisingly small changes on lipid metabolism, as assessed by radiolabelling from [1- 14C]acetate. The main effects, which were seen in a number of cases, were an overall inhibition of total lipid labelling and a relative increase in the labelling of triacylglycerols in the non-polar fraction. Both of these changes can be viewed as reflecting general toxicity of heavy metals. The Coccomyxa photobiont species were more sensitive than Trebouxia species, which fits with the general distribution of the latter in lichens inhabiting harsh environments.

Photobiont Diversity in the Physciaceae (Lecanorales)

Newly designed algal-specific primers were used to amplify the ribosomal ITS region from 25 photobiont specimens from five lichenized fungi of the family Physciaceae (Lecanorales), Anaptychia ciliaris, Phaeophyscia orbicularis, Physcia caesia, P. tenella, and Physconia distorta. The obtained DNA sequences were then phylogenetically analyzed using parsimony jackknifing. The analyses indicated that the mycobionts associated with two photobiont species: Trebouxia impressa was found with all mycobionts, except Anaptychia ciliaris, which instead was associated with Trebouxia arboricola. In the jackknife tree, all Trebouxia arboricola sequences formed a monophyletic group with a high jackknife support. The Trebouxia impressa sequences also formed a well supported group, which in turn had some internal structure. The photobiont species is reported for the first time for Anaptychia ciliaris, Physcia caesia, and P. tenella. A phylogenetic tree for the photobiont, T. impressa, was compared to a phylogeny of the corresponding mycobionts, also based on ITS sequences. A combined analysis of the data from the photobiont and the data from the mycobiont was also performed. Several similarities were found in the tree topologies. The general similarity of the mycobiont and photobiont trees may indicate a coevolutionary history.

Identification of photobionts from the lichen family Physciaceae using algal-specific ITS rDNA sequencing

Abstract:The identity of photobionts from 20 species of the Physciaceae from different habitats and geographical regions has been determined by ITS rDNA sequence comparisons in order to estimate the diversity of photobionts within that lichen group, to detect patterns of specificity of mycobionts towards their photobionts and as a part of an ongoing study to investigate possible parallel cladogenesis of both symbionts. Algal-specific PCR primers have been used to determine the ITS rDNA sequences from DNA extractions of dried lichens that were up to 5 years old. Direct comparisons and phylogenetic analyses allowed the assignment of Physciaceae photobionts to four distinct clades in the photobiont ITS rDNA phylogeny. The results indicate a diversity within the genus Trebouxia Puymaly and Physciaceae photobionts that is higher than expected on the basis of morphology alone. Physciaceae photobionts belonged to 12 different ITS lineages of which nine could unambiguously be assigned to six morphospecies of Trebouxia. The identity of the remaining three sequences was not clarified; they may represent new species. Specificity at the generic level was low as a whole range of photobiont species were found within a genus of Physciaceae and different ranges were detected. The photobionts ofPhyscia (Schreb.) Michaux were closely related and represented one morphospecies of Trebouxia, whereas the algal partners of Buellia De Not and Rinodina (Ach.) S. Gray were in distant lineages of the ITS phylogeny and from several Trebouxia morphospecies. Photobiont variation within a genus of Physciaceae may be due to phylogeny, geographical distance or because photobionts from neighbouring lichens were taken (‘algal sharing’). At the species level Physciaceae mycobionts seem to be rather selective and contained photobionts that were very closely related within one morphospecies of Trebouxia.

PHOTOBIONT INVENTORY OF A LICHEN COMMUNITY GROWING ON HEAVY-METAL-RICH ROCK

Abstract: The photobiont inventory of a stand of the Acarosporetum sinopicae, a lichen community comprising saxicolous, chalcophilous lichens, has been analysed. Investigated lichen species were Acarospora rugulosa, A. sinopica, Bellemerea diamartha, Lecanora polytropa, L. subaurea, Lecidea silacea, L. lapicida, Rhizocarpon geographicum, and Umbilicaria cylindrica. For all these lichen species this is the first record of the photobionts, except for L. lapicida. The photobionts were cultured axenically and investigated using light microscopical and molecular methods (ITS-sequence analyses). Every lichen species contained only one photobiont species. All photobionts belong toTrebouxia jamesii , but two different subspecies were found with the morphological differences corresponding to molecular differences. The new subspecies T. jamesii subsp. angustilobata is described, differing from the typical T. jamesii by a crenulate chloroplast but identical to the latter taxon in respect to the pyrenoid structure in the light microscope. These results are discussed with respect to the photobiont inventory of the Physcietum adscendentis, analysed in an earlier study.

Selectivity of photobiont choice in a defined lichen community: inferences from cultural and molecular studies

Axenic cultures of lichen photobionts isolated from bark‐inhabiting lichen thalli of the Physcietum adscendentis Ochsner were identified by light microscopy and sequence comparisons of internal transcribed spacer rDNAs to investigate principles of lichenization within a defined lichen sociological unit. The photobiont identity of eight lichen species is reported for the first time (photobiont species in square brackets): Lecania cyrtella (Ach.) Th. Fr. [Trebouxia arboricola Puym.], Lecania naegelii (Hepp) Diederich & v. d. Boom [Dictyochloropsis symbiontica Tscherm.‐Woess], Candelaria concolor (Dicks) B. Stein [Trebouxia jamesii (Hildreth & Ahmadjian) Gärtner], Candelariella cf. reflexa (Nyl.) Lettau [T. jamesii], Lecanora spec. [T. arboricola], Phaeophyscia orbicularis (Neck.) Moberg [T. impressa Ahmadjian], Physcia adscendens (Fr.) H. Olivier [T. impressa] and Lecidella elaeochroma (Ach.) M. Choisy [T. arboricola] and could be confirmed for another two species, Physcia stellaris (L.) Nyl. [Trebouxia impressa] and Xanthoria parietina (L.) Th. Fr. [Trebouxia arboricola]. The observation that pioneer lichens without vegetative propagules, growing on smooth bark, had Trebouxia arboricola as photobiont can be explained by the assumption of a free‐living population of Trebouxia arboricola. Species of photobionts from Xanthoria parietina were morphologically and genetically different from those of Physcia adscendens and Phaeophyscia orbicularis, respectively; a finding that does not support the previous assumption that Xanthoria parietina takes over its algal partner from a Physcia species, at least at the sites investigated.