Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea

[EN] The precise boundary delineations between taxa in symbiotic associations are very important for evolutionary and ecophysiological studies. Growing evidence indicates that in many cases, the use of either morphological characters or molecular markers results in diversity underestimation. In lichen symbioses. Trebouxia is the most common genus of lichen phycobionts, however, the diversity within this genus has been poorly studied and as such there is no clear species concept. This study constitutes a multifaceted approach incorporating aspects of ultrastructural characterization by TEM and phylogenomics to evaluate the morphological and genetic diversity of phycobionts within the sexually reproducing lichen Ramalina fraxinea in the context of Mediterranean and temperate populations. Results reveal an association with at least seven different Trebouxia lineages belonging to at least two species. T. decolorans and T. jamesii, and diverse combinations of such lineages coexisting within the same thallus depending on the analysed sample. Some of these lineages are shared by several other non-related lichen taxa. Our findings indicate the existence of a highly diverse assemblage of Trebouxia algae associating with R. fraxinea and suggest a possible incipient speciation within T. decolorans rendering a number of lineages or even actual species. This study stresses the importance of coordinated ultrastructural and molecular analyses to improve estimates of diversity and reveal the coexistence of more than one Trebouxia species within the same thallus. lt is also necessary to have clearer species delimitation criteria within the genus Trebouxia and microalgae in general.This study was funded by the Ministerio de Economia y Competitividad (MINECO CGL2012-40058-0O2-01/02), FEDER, the Generalitat Valenciana (PROMETEOII2013/021, GVA) and the Direccion General de Universidades e Investigacion de la Consejeria de Educacion de la Comunidad de Madrid - Universidad de Alcala (CCG10-UAH/GEN-5904). Drs. Arantxa Matins and Patricia Moya (Universitat de Valencia) made helpful comments on the manuscript.Català, S.; Campo, ED.; Barreno, E.; García-Breijo, F.; Reig Armiñana, J.; Casano, L. (2016). Coordinated ultrastructural and phylogenomic analyses shed light on the hidden phycobiont diversity of Trebouxia microalgae in Ramalina fraxinea. Molecular Phylogenetics and Evolution. 94:765-777. https://doi.org/10.1016/j.ympev.2015.10.021S7657779

Sunlight-Exposed Biofilm Microbial Communities Are Naturally Resistant to Chernobyl Ionizing-Radiation Levels

BACKGROUND: The Chernobyl accident represents a long-term experiment on the effects of exposure to ionizing radiation at the ecosystem level. Though studies of these effects on plants and animals are abundant, the study of how Chernobyl radiation levels affect prokaryotic and eukaryotic microbial communities is practically non-existent, except for a few reports on human pathogens or soil microorganisms. Environments enduring extreme desiccation and UV radiation, such as sunlight exposed biofilms could in principle select for organisms highly resistant to ionizing radiation as well. METHODOLOGY/PRINCIPAL FINDINGS: To test this hypothesis, we explored the diversity of microorganisms belonging to the three domains of life by cultivation-independent approaches in biofilms developing on concrete walls or pillars in the Chernobyl area exposed to different levels of radiation, and we compared them with a similar biofilm from a non-irradiated site in Northern Ireland. Actinobacteria, Alphaproteobacteria, Bacteroidetes, Acidobacteria and Deinococcales were the most consistently detected bacterial groups, whereas green algae (Chlorophyta) and ascomycete fungi (Ascomycota) dominated within the eukaryotes. Close relatives to the most radio-resistant organisms known, including Rubrobacter species, Deinococcales and melanized ascomycete fungi were always detected. The diversity of bacteria and eukaryotes found in the most highly irradiated samples was comparable to that of less irradiated Chernobyl sites and Northern Ireland. However, the study of mutation frequencies in non-coding ITS regions versus SSU rRNA genes in members of a same actinobacterial operational taxonomic unit (OTU) present in Chernobyl samples and Northern Ireland showed a positive correlation between increased radiation and mutation rates. CONCLUSIONS/SIGNIFICANCE: Our results show that biofilm microbial communities in the most irradiated samples are comparable to non-irradiated samples in terms of general diversity patterns, despite increased mutation levels at the single-OTU level. Therefore, biofilm communities growing in sunlight exposed substrates are capable of coping with increased mutation rates and appear pre-adapted to levels of ionizing radiation in Chernobyl due to their natural adaptation to periodical desiccation and ambient UV radiation

Aspects of photobiont selectivity in lichens

Um einen cberblick \ufcber die Trebouxia Phylogenie zu erhalten wurden Photobionten verschiedener Flechten analysiert. Es wurden B\ue4ume der 4 Hauptclades von Trebouxia (A, I, G, S) berechnet, um einen cberblick zu gewinnen. Um die Photobionten Spezifit\ue4t in Flechten mit unterschiedlicher Symbionten Selektivit\ue4t zu untersuchen, wurden Daten von unterschiedlichen Flechten untersucht. Es zeigt sich, dass sich die Photobionten Selektivit\ue4t in verschiedenen Flechten stark unterscheiden. Pairwise Mismatch Distributions wurden benutzt um die Unterschiede in den Photobionten Assoziationen darzustellen und diese wurden mit den phylogenetischen B\ue4umen verglichen. Weiters wurden Unterschiede zwischen Flechten mit unterschiedlichen Reproduktionsstrategien untersucht. Diese sollten deutliche Unterschiede in ihren Populationsstrukturen zeigen. Um diese Unterschiede zu untersuchen, wurden zwei eng verwandte Flechten mit unterschiedlichen Reproduktionsstrategien, entlang eines Nord-S\ufcd Gradienten analysiert. Es wurde die Populationsstruktur beider Symbionten und ihre Symbionten Selektivit\ue4t untersucht. Es wurde keine deutliche Assoziation der Genotypen der Symbionten in der Flechte mit vegetativer, gleichzeitiger Ausbreitung der Symbionten gefunden. Es zeigt sich dass die Algen-Gendiversit\ue4t in Flechten mit unterschiedlichen Ausbreitungsstragien gleich stark schwankt. Die aktive Aufnahme von Algen w\ue4hrend der vegetativen Entwicklung des Thallus ist die wahrscheinlichste Erkl\ue4rung f\ufcr dieses Muster. Die gleichzeitige Ausbreitung beider Symbionten stellt also nur eine zus\ue4tzliche M\uf6glichkeit der Ausbreitung dar.Photobionts from different lichens have been analysed to gain insight in the overall diversity of lichenized Trebouxia to show an overall phylogeny. For this purpose trees of Trebouxia of the 4 major clades (A, I, G, S) have been calculated. To assess algal specificity in lichens with a different degree of symbiont selectivity data from different lichen species have been analysed. The results clearly show that patterns of photobiont selectivity vary strongly among lichens species. Pairwise mismatch distributions are used to illustrate patterns of photobiont associations and compared with the phylogenetic distribution of the photobionts from the same data. Differences between species that differ in their propagation mode should ideally be reflected by dissimilar population genetic structures of both symbionts. To test this hypothesis, in populations of two closely related lichen species which differ in their reproductive modes, the population structure of both symbionts following a North-South gradient was investigated. This was used to assess the population structure of both symbionts and symbiont selectivity patterns. A pronounced degree of association of symbiont genotypes was not confirmed in the lichen with joint symbiont dispersal and it is shown that algal gene diversities in populations of lichens with different propagation strategies are within the same range. Apparently, these lichens with different propagation strategies do not vary in their photobiont diversity. I suggest that uptake of other algae during the vegetative development of the thalli is the most likely explanation for the observed pattern. Vertical transmission of symbiotic associations is a possibility but not a necessity in soredial reproduction of lichens.Sabine WornikAbweichender Titel laut cbersetzung der Verfasserin/des VerfassersGraz, Univ., Diss., 200

Antioxidants and photoprotection in a lichen as compared with its isolated symbiotic partners

Extreme desiccation and irradiation increase the formation of reactive oxygen species in organisms. Lichens are highly resistant to potential damage, but it is not known whether biochemical interaction between their fungal and algal partners is involved in conferring stress tolerance. Here, we show that antioxidant and photoprotective mechanisms in the lichen Cladonia vulcani are more effective by orders of magnitude than those of its isolated partners. When alone, both alga and fungus suffer oxidative damage during desiccation, but in the lichen, each appears to induce up-regulation of protective systems in the other. Without the fungal contact, the alga tolerates only very dim light and its photoprotective system is only partially effective; without the alga, the glutathione-based antioxidant system of the fungus is slow and ineffective. In the lichen, this mutually enhanced resistance to oxidative stress and, in particular, its desiccation tolerance are essential for life above ground. This lifestyle, in turn, increases the chance of dispersal of reproductive propagules and ensures their joint evolutionary success

The symbiotic playground of lichen thalli - a highly flexible photobiont association in rock-inhabiting lichens

The development of characteristic thallus structures in lichen-forming fungi requires the association with suitable photoautotrophic partners. Previous work suggests that fungi have a specific range of compatible photobionts and that selected algal strains are also correlated with the habitat conditions. We selected the rock-inhabiting crust lichen Protoparmeliopsis muralis, which exhibits high flexibility in algal associations. We present a geographically extended and detailed analysis of algal association patterns including thalli which host superficial algal colonies. We sampled 17 localities in Europe, and investigated the photobiont genotypic diversity within and between thalli and compared the diversity of intrathalline photobionts and externally associate algal communities between washed and unwashed thalli by single-strand conformation polymorphism analyses and ITS sequence data. The results show that (1) photobiont population within the lichen thalli is homogeneous; (2) multiple photobiont genotypes occur within single areoles and lobes of individual lichens; and (3) algal communities which superficially colonize the lichen thalli host taxa known as photobionts in unrelated lichens. Photobiont association patterns are extremely flexible in this ecologically versatile crust-forming lichen. We suggest that lichen surfaces represent a potential temporary niche for free-living stages of lichen photobionts, which could facilitate the establishment of further lichens in the proximal area

Mutualisms in a changing world: an evolutionary perspective.

There is growing concern that rapid environmental degradation threatens mutualistic interactions. Because mutualisms can bind species to a common fate, mutualism breakdown has the potential to expand and accelerate effects of global change on biodiversity loss and ecosystem disruption. The current focus on the ecological dynamics of mutualism under global change has skirted fundamental evolutionary issues. Here, we develop an evolutionary perspective on mutualism breakdown to complement the ecological perspective, by focusing on three processes: (1) shifts from mutualism to antagonism, (2) switches to novel partners and (3) mutualism abandonment. We then identify the evolutionary factors that may make particular classes of mutualisms especially susceptible or resistant to breakdown and discuss how communities harbouring mutualisms may be affected by these evolutionary responses. We propose a template for evolutionary research on mutualism resilience and identify conservation approaches that may help conserve targeted mutualisms in the face of environmental change. © 2010 Blackwell Publishing Ltd/CNRS