Microbial response to seasonal variation in arctic biocrusts with a focus on fungi and cyanobacteria.

Biocrusts are crucial components of Arctic ecosystems, playing significant roles in carbon and nitrogen cycling, especially in regions where plant growth is limited. However, the microbial communities within Arctic biocrusts and their strategies for surviving the harsh conditions remain poorly understood. In this study, the microbial profiles of Arctic biocrusts across different seasons (summer, autumn, and winter) were investigated in order to elucidate their survival strategies in extreme conditions.

Metagenomic Analysis of Antarctic Biocrusts Unveils a Rich Range of Cold-Shock Proteins.

Microorganisms inhabiting Antarctic biocrusts develop several strategies to survive extreme environmental conditions such as severe cold and drought. However, the knowledge about adaptations of biocrusts microorganisms are limited. Here, we applied metagenomic sequencing to study biocrusts from east Antarctica.

Metagenomics Provides a Deeper Assessment of the Diversity of Bacterial Communities in Polar Soils Than Metabarcoding.

The diversity of soil bacteria was analyzed via metabarcoding and metagenomic approaches using DNA samples isolated from the biocrusts of 12 different Arctic and Antarctic sites. For the metabarcoding approach, the V3-4 region of the 16S rRNA was targeted. Our results showed that nearly all operational taxonomic units (OTUs = taxa) found in metabarcoding analyses were recovered in metagenomic analyses.

Biocrusts from Iceland and Svalbard: Does microbial community composition differ substantially?

A wide range of microorganisms inhabit biocrusts of arctic and sub-arctic regions. These taxa live and thrive under extreme conditions and, moreover, play important roles in biogeochemical cycling. Nevertheless, their diversity and abundance remain ambiguous.

Temperature- and light stress adaptations in Zygnematophyceae: The challenges of a semi-terrestrial lifestyle.

Streptophyte green algae comprise the origin of land plants and therefore life on earth as we know it today. While terrestrialization opened new habitats, leaving the aquatic environment brought additional abiotic stresses. More-drastic temperature shifts and high light levels are major abiotic stresses in semi-terrestrial habitats, in addition to desiccation, which has been reviewed elsewhere.

Desiccation tolerance in streptophyte algae and the algae to land plant transition: evolution of LEA and MIP protein families within the Viridiplantae.

The present review summarizes the effects of desiccation in streptophyte green algae, as numerous experimental studies have been performed over the past decade particularly in the early branching streptophyte Klebsormidium sp. and the late branching Zygnema circumcarinatum. The latter genus gives its name to the Zygenmatophyceae, the sister group to land plants.

Metatranscriptomic and metabolite profiling reveals vertical heterogeneity within a Zygnema green algal mat from Svalbard (High Arctic).

Within streptophyte green algae Zygnematophyceae are the sister group to the land plants that inherited several traits conferring stress protection. Zygnema sp., a mat-forming alga thriving in extreme habitats, was collected from a field site in Svalbard, where the bottom layers are protected by the top layers.

Cold Acclimation Improves the Desiccation Stress Resilience of Polar Strains of (Streptophyta).

Biological soil crusts (BSCs) are complex communities of autotrophic, heterotrophic, and saprotrophic (micro)organisms. In the polar regions, these biocrust communities have essential ecological functions such as primary production, nitrogen fixation, and ecosystem engineering while coping with extreme environmental conditions (temperature, desiccation, and irradiation). The microalga is commonly found in BSCs all across the globe.

Biodiversity of biological soil crusts from the Polar Regions revealed by metabarcoding.

Biological soil crusts (BSCs) are amalgamations of autotrophic, heterotrophic and saprotrophic organisms. In the Polar Regions, these unique communities occupy essential ecological functions such as primary production, nitrogen fixation and ecosystem engineering. Here, we present the first molecular survey of BSCs from the Arctic and Antarctica focused on both eukaryotes and prokaryotes as well as passive and active biodiversity.

New barcoded primers for efficient retrieval of cercozoan sequences in high-throughput environmental diversity surveys, with emphasis on worldwide biological soil crusts.

We describe the performance of a new metabarcoding approach to investigate the environmental diversity of a prominent group of widespread unicellular organisms, the Cercozoa. Cercozoa is an immensely large group of protists, and although it may dominate in soil and aquatic ecosystems, its environmental diversity remains undersampled. We designed PCR primers targeting the hypervariable region V4 of the small subunit ribosomal RNA (SSU or 18S) gene, which is the recommended barcode marker for Cercozoa.

Enhanced Desiccation Tolerance in Mature Cultures of the Streptophytic Green Alga Zygnema circumcarinatum Revealed by Transcriptomics.

Desiccation tolerance is commonly regarded as one of the key features for the colonization of terrestrial habitats by green algae and the evolution of land plants. Extensive studies, focused mostly on physiology, have been carried out assessing the desiccation tolerance and resilience of the streptophytic genera Klebsormidium and Zygnema. Here we present transcriptomic analyses of Zygnema circumcarinatum exposed to desiccation stress.

The Origin and Evolution of the Plant Cell Surface: Algal Integrin-Associated Proteins and a New Family of Integrin-Like Cytoskeleton-ECM Linker Proteins.

The extracellular matrix of scaly green flagellates consists of small organic scales consisting of polysaccharides and scale-associated proteins (SAPs). Molecular phylogenies have shown that these organisms represent the ancestral stock of flagellates from which all green plants (Viridiplantae) evolved. The molecular characterization of four different SAPs is presented.

The impact of GSTM1/GSTT1 polymorphism for the risk of oral cancer.

Objectives: Since development of oral squamous cell cancer (OSCC) is triggered by various noxa, different variants of the antioxidant glutathione S-transferases (GSTs) can counteract toxic compounds (e.g., tobacco smoke).

Transcriptomics of desiccation tolerance in the streptophyte green alga Klebsormidium reveal a land plant-like defense reaction.

Background: Water loss has significant effects on physiological performance and survival rates of algae. However, despite the prominent presence of aeroterrestrial algae in terrestrial habitats, hardly anything is known about the molecular events that allow aeroterrestrial algae to survive harsh environmental conditions. We analyzed the transcriptome and physiology of a strain of the alpine aeroterrestrial alga Klebsormidium crenulatum under control and strong desiccation-stress conditions.

The contractile vacuole as a key regulator of cellular water flow in Chlamydomonas reinhardtii.

Most freshwater flagellates use contractile vacuoles (CVs) to expel excess water. We have used Chlamydomonas reinhardtii as a green model system to investigate CV function during adaptation to osmotic changes in culture medium. We show that the contractile vacuole in Chlamydomonas is regulated in two different ways.

Snow ball earth and the split of Streptophyta and Chlorophyta.

About 700 million years ago (Mya), the ancestor of all green plants evolved into two major groups: the Chlorophyta (many green algae) and the Streptophyta (some green algae and land plants = embryophytes). Both groups are separated by several morphological, physiological, and molecular characteristics, including different photorespiration pathways. The Chloropyhta/Streptophyta split was probably very important for the colonization of the terrestrial habitat because embryophytes, the descendants of streptophyte algae, today completely dominate the macrophyte flora of the terrestrial habitats.

The SEC6 protein is required for contractile vacuole function in Chlamydomonas reinhardtii.

Contractile vacuoles (CVs) are essential for osmoregulation in many protists. To investigate the mechanism of CV function in Chlamydomonas, we isolated novel osmoregulatory mutants. Four of the isolated mutant cell lines carried the same 33,641 base deletion, rendering the cell lines unable to grow under strong hypotonic conditions.

Origin of land plants: do conjugating green algae hold the key?

Background: The terrestrial habitat was colonized by the ancestors of modern land plants about 500 to 470 million years ago. Today it is widely accepted that land plants (embryophytes) evolved from streptophyte algae, also referred to as charophycean algae. The streptophyte algae are a paraphyletic group of green algae, ranging from unicellular flagellates to morphologically complex forms such as the stoneworts (Charales).

The system of contractile vacuoles in the green alga Mesostigma viride (Streptophyta).

The contractile vacuole (CV) is an osmoregulatory organelle which is found in many protists. We have investigated the structure and function of the CV in the green alga Mesostigma viride by light (video) and serial section electron microscopy. Mesostigma is the only known flagellate streptophyte (charophycean green algae and land plants) and therefore of great importance for our understanding of the evolution of streptophytes.

Streptophyte algae and the origin of embryophytes.

Background: Land plants (embryophytes) evolved from streptophyte green algae, a small group of freshwater algae ranging from scaly, unicellular flagellates (Mesostigma) to complex, filamentous thalli with branching, cell differentiation and apical growth (Charales). Streptophyte algae and embryophytes form the division Streptophyta, whereas the remaining green algae are classified as Chlorophyta. The Charales (stoneworts) are often considered to be sister to land plants, suggesting progressive evolution towards cellular complexity within streptophyte green algae.

Chlamydial genes shed light on the evolution of photoautotrophic eukaryotes.

Background: Chlamydiae are obligate intracellular bacteria of protists, invertebrates and vertebrates, but have not been found to date in photosynthetic eukaryotes (algae and embryophytes). Genes of putative chlamydial origin, however, are present in significant numbers in sequenced genomes of photosynthetic eukaryotes. It has been suggested that such genes were acquired by an ancient horizontal gene transfer from Chlamydiae to the ancestor of photosynthetic eukaryotes.

Function and evolution of the vacuolar compartment in green algae and land plants (Viridiplantae).

Plant vacuoles perform several different functions and are essential for the plant cell. The large central vacuoles of mature plant cells provide structural support, and they serve other functions, such as protein degradation and turnover, waste disposal, storage of metabolites, and cell growth. A unique feature of the plant vacuolar system is the presence of different types of vacuoles within the same cell.

Gain and loss of polyadenylation signals during evolution of green algae.

Background: The Viridiplantae (green algae and land plants) consist of two monophyletic lineages: the Chlorophyta and the Streptophyta. Most green algae belong to the Chlorophyta, while the Streptophyta include all land plants and a small group of freshwater algae known as Charophyceae. Eukaryotes attach a poly-A tail to the 3' ends of most nuclear-encoded mRNAs.

Phylogenetic analyses of nuclear, mitochondrial, and plastid multigene data sets support the placement of Mesostigma in the Streptophyta.

All extant green plants belong to 1 of 2 major lineages, commonly known as the Chlorophyta (most of the green algae) and the Streptophyta (land plants and their closest green algal relatives). The scaly green flagellate Mesostigma viride has an important place in the debate on the origin of green plants. However, there have been conflicting results from molecular systematics as to whether Mesostigma diverges before the Chlorophyta/Streptophyta split or is an early diverging flagellate member of the Streptophyta.