The Lichens' Microbiota, Still a Mystery?

Maria Grimm,Martin Grube,Jörg Bernhardt,Katharina Riedel,Ulf Schiefelbein,Daniela Zühlke

doi:10.3389/fmicb.2021.623839

Maria Grimm, Martin Grube + Show 4 more

Open Access

https://doi.org/10.3389/fmicb.2021.623839

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Abstract

Lichens represent self-supporting symbioses, which occur in a wide range of terrestrial habitats and which contribute significantly to mineral cycling and energy flow at a global scale. Lichens usually grow much slower than higher plants. Nevertheless, lichens can contribute substantially to biomass production. This review focuses on the lichen symbiosis in general and especially on the model species Lobaria pulmonaria L. Hoffm., which is a large foliose lichen that occurs worldwide on tree trunks in undisturbed forests with long ecological continuity. In comparison to many other lichens, L. pulmonaria is less tolerant to desiccation and highly sensitive to air pollution. The name-giving mycobiont (belonging to the Ascomycota), provides a protective layer covering a layer of the green-algal photobiont (Dictyochloropsis reticulata) and interspersed cyanobacterial cell clusters (Nostoc spec.). Recently performed metaproteome analyses confirm the partition of functions in lichen partnerships. The ample functional diversity of the mycobiont contrasts the predominant function of the photobiont in production (and secretion) of energy-rich carbohydrates, and the cyanobiont’s contribution by nitrogen fixation. In addition, high throughput and state-of-the-art metagenomics and community fingerprinting, metatranscriptomics, and MS-based metaproteomics identify the bacterial community present on L. pulmonaria as a surprisingly abundant and structurally integrated element of the lichen symbiosis. Comparative metaproteome analyses of lichens from different sampling sites suggest the presence of a relatively stable core microbiome and a sampling site-specific portion of the microbiome. Moreover, these studies indicate how the microbiota may contribute to the symbiotic system, to improve its health, growth and fitness.

Highlights

Evolution is replenished with examples of symbiotic life forms, which often include great examples of emergent metabolic solutions and joint morphologies
More than 20 years later, diversity and specificity was studied in more detail by culture-independent sequencing approaches, and later by more sophisticated omics technologies, which demonstrated that lichens are furnished with a complex bacterial microbiome (Figure 1) (e.g., González et al, 2005; Cardinale et al, 2006; Liba et al, 2006; Grube et al, 2009; Selbmann et al, 2010; Bates et al, 2011; Hodkinson et al, 2012; Aschenbrenner et al, 2014)
Metaorganisms such as lichens consist of highly integrated partnerships reflecting the classical dual definitions of the lichen symbiosis, and less tightly integrated partners with auxiliary functions (Hyvärinen et al, 2002; Cornejo and Scheidegger, 2013)

Summary

Introduction

Evolution is replenished with examples of symbiotic life forms, which often include great examples of emergent metabolic solutions and joint morphologies. More than 20 years later, diversity and specificity was studied in more detail by culture-independent sequencing approaches, and later by more sophisticated omics technologies, which demonstrated that lichens are furnished with a complex bacterial microbiome (Figure 1) (e.g., González et al, 2005; Cardinale et al, 2006; Liba et al, 2006; Grube et al, 2009; Selbmann et al, 2010; Bates et al, 2011; Hodkinson et al, 2012; Aschenbrenner et al, 2014).

Results

Conclusion