Klebsormidin A and B, Two New UV-Sunscreen Compounds in Green Microalgal Interfilum and Klebsormidium Species (Streptophyta) From Terrestrial Habitats.

Anja Hartmann,Andreas Holzinger,Karin Glaser,Markus Ganzera,Ulf Karsten

doi:10.3389/fmicb.2020.00499

Anja Hartmann, Andreas Holzinger + Show 3 more

Open Access

https://doi.org/10.3389/fmicb.2020.00499

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Abstract

The terrestrial green algal members of the genera Interfilum and Klebsormidium (Klebsormidiophyceae, Streptophyta) are found in biological soil crusts of extreme habitats around the world where they are regularly exposed, among other abiotic stress factors, to high levels of ultraviolet radiation (UVR). As a consequence those species synthesize and accumulate either one or two mycosporine-like amino acids (MAAs), but with a missing structural elucidation up to now. Therefore, in the present study both MAAs were chemically isolated and structurally elucidated. The two new compounds exhibit absorption maxima of 324 nm. MAA 1 has a molecular weight of 467 and MAA 2 of 305, and the latter (MAA 2) was identified as N-(4,5-dihydroxy-5-(hydroxymethyl)-2-methoxy-3-oxocyclohex-1-en-1-yl)-N-methylserine using one- and two-dimensional 1H and 13C-NMR spectroscopy. MAA 1 contains an additional sugar moiety. As trivial names for these two novel MAAs we suggest klebsormidin A and klebsormidin B. Different species from all previously described phylogenetic clades of Klebsormidiophyceae were chemically screened for their MAA composition in aqueous extracts using RP−HPLC and LC−MS. The novel klebsormidin A was present throughout all clades and hence could be suitable as a chemotaxonomic marker. Additionally, controlled UVR−exposure experiments with all investigated species showed that MAA biosynthesis and intracellular enrichment is strongly induced by short wavelengths, supporting the function of these compounds as natural UV−sunscreen as well as explaining the cosmopolitan distribution and ecological success of Interfilum and Klebsormidium in terrestrial habitats.

Highlights

Biological soil crusts are regarded as lower vegetation form or cryptogamic cover, and these communities dominate drylands and disturbed ecosystems worldwide, and are well described as biodiversity and activity hotspots (Weber et al, 2016)
The hydroalcoholic extract of Klebsormidium crenulatum was first fractionated on a Sephadex LH-20 column, and in a final purification step using semi-preparative High-PerformanceLiquid Chromatography (HPLC) three UV-absorbing compounds were isolated
The mass deviation is

Summary

Introduction

Biological soil crusts (biocrusts) are regarded as lower vegetation form or cryptogamic cover, and these communities dominate drylands and disturbed ecosystems worldwide, and are well described as biodiversity and activity hotspots (Weber et al, 2016). Biocrusts are build up by living heterotrophic and phototrophic microorganisms which include bacteria, archaea, microfungi, unicellular and filamentous cyanobacteria and algae This community can be considered as “joint venture” and “ecosystem-engineers” because as microbial activity hotspots they are important for supporting and maintaining ecosystem multifunctionality. Most interesting is the observation that the assigned Klebsormidium lineages reflect different terrestrial habitats (Ryšánek et al, 2015), i.e., members of superclade E, for example, preferentially occur under rather humid conditions (e.g., temperate Europe) Those of superclade G are mainly found under xerophytic conditions (e.g., drylands South Africa) (Mikhailyuk et al, 2015; Samolov et al, 2019)

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