374 research outputs found
Invading grass-like alga transforms rippled sand bars into bumpy muddy flats: arrival of a game changer in the Wadden Sea
Get PDFIn the wake of biological globalization, translocated species of high bio-engineering capacity increasingly change bottom topography of sedimentary coasts. A Vaucheria-taxon (Xanthophyceae) of unknown origin is spreading at the transition between intertidal and subtidal zones, while resident Vaucheria-species are confined to the upper shore in the Wadden Sea (European Atlantic). Near the island of Sylt, dense turfs of green filaments rapidly expanded over an area of 180 ha within 3 years. The unicellular filaments reach about 5 cm out of and 5 cm into the sediment. Felted rhizoids provide firm anchorage. Dry phytomass (up to 208 g m-2) was similar to that of intertidal seagrass beds. Residual filaments overwinter in the sediment and give rise to renewed growth in late spring. In addition, oospores germinate. Fine particles are trapped by the turf during summer, generating laminated cohesive mud. Muddy hummocks arise up to 20 cm above ambient sand flats, alternating with troughs but gradually merge into coherent and pertinacious plateaus of mud. This shift in bottom topography and sediment composition may potentially change the mud balance of tidal basins, and the capacity of tidal flats in catching up with accelerating sea-level rise
Influence of Different CO2 Concentrations on Microalgae Growth, alpha-Tocopherol Content and Fatty Acid Composition
No full textA prerequisite for the growth of microalgae on an industrial scale is the optimization of cultivation conditions and the reduction of production costs. The nutrient elements, heat and carbon dioxide provided by flue gas can be used to increase biomass production. The aim of this study was to investigate the effects of different CO2 concentrations on algal strains with regard to biomass production, alpha-tocopherol content, fatty acid composition and fatty acid content. For this, we grew the three microalgae Coccomyxa sp., Desmodesmus sp. and Muriella terrestris that were isolated from two tufa-forming karstwater creeks characterized by high CO2 partial pressures. No significant differences in biomass production rate were observed when the cultures were gassed with air or 15% (v/v) CO2. However, cell growth increased substantially when 5% (v/v) CO2 was used. The content of alpha-tocopherol increased in the stationary phase compared to the logarithmic phase in all investigated strains. In contrast, it decreased significantly when the cultures were aerated with either 5% (v/v) CO2 or 15% (v/v) CO2. The saturation level of fatty acids was significantly higher in cultures aerated with CO2 in the stationary phase compared to the logarithmic phase. In contrast, it decreased in the stationary phase when the cultures were gassed with air. Fatty acid contents increased in the stationary phase compared to the logarithmic phase. It was also higher by gassing with 5% (v/v) CO2 and decreased when the cultures were aerated with air or 15% (v/v) CO2. When the biomass production rates were taken into consideration together with contents of alpha-tocopherol and total fatty acid, the productivity of both increased considerably when the cultures experienced gassing by a 5% (v/v) CO2
From single pioneers to complex pro- and eukaryotic microbial networks in soils along a glacier forefield chronosequence in continental Antarctica
No full textIntroduction In the extremely dry and oligotrophic soils of East Antarctica, where low temperatures and humidity result in minimal biological turnover rates, extracellular DNA (eDNA) can persist over extended timescales. Differentiating between sequences from living, potentially active cells (intracellular DNA, or iDNA) and those from ancient, non-living organisms (eDNA) is crucial for accurately assessing the current microbial community and understanding historical microbial dynamics. Methods This study was conducted along a chronosequence in the Larsemann Hills, East Antarctica, where soil samples were collected from sites at varying distances from the glacier. By employing DNA separation methods, we distinguished iDNA, which represents living cells, from eDNA derived from dead organisms. High-throughput sequencing was used to characterize bacterial and eukaryotic communities across different successional stages. Results The DNA separation approach revealed distinct bacterial and eukaryotic community structures along the glacier transect. Actinobacteria were consistently abundant across all sites, while other phyla such as Chloroflexi, Gemmatimonadetes, and Proteobacteria thrived in extreme, nutrient-poor environments. Early successional stages were characterized by the simultaneous colonization of green algae Trebouxiophyceae and cryophilic fungi, alongside nitrogen-fixing bacteria, which contributed to initial soil development. The study also identified three distinct modes of microbial distribution, reflecting varying degrees of activity and adaptability. Discussion Our findings provide new insights into microbial dynamics in extreme habitats and propose new hypotheses for microbial colonization in newly exposed soils. Moreover, they contribute to the ongoing debate in microbial ecology regarding the viability of dormant or dead cells and emphasize the need for refining DNA-based methods and exploring functional pathways to deepen our understanding of microbial succession in polar regions
MICROALGAE COMMUNITIES IN ANTARCTIC SOILS: CHANGES ALONG SOIL DEVELOPMENTAL STAGES AND TESTING FOR GEOGRAPHICAL DISTRIBUTION
No full textThe Long chain Diol Index: A marine palaeotemperature proxy based on eustigmatophyte lipids that records the warmest seasons
No full textLong chain 1,13- and 1,15-diols are lipids which are omnipresent in marine environments, and the Long chain Diol Index (LDI), based on their distributions, has previously been introduced as a proxy for sea surface temperature. The main biological sources for long chain 1,13- and 1,15-diols have remained unknown, but our combined lipid and 23S ribosomal RNA (23S rRNA) analyses on suspended particulate matter from the Mediterranean Sea demonstrate that these lipids are produced by a marine eustigmatophyte group that originated before the currently known eustigmatophytes diversified. The 18S rRNA data confirm the existence of early-branching marine eustigmatophytes, which occur at a global scale. Differences between LDI records and other paleotemperature proxies are generally attributed to differences between the seasons in which the proxy-related organisms occur. Our results, combined with available LDI data from surface sediments, indicate that the LDI primarily registers temperatures from the warmest month when mixed-layer depths, salinity, and nutrient concentrations are low. The LDI may not be applicable in areas where Proboscia diatoms contribute 1,13-diols, but this can be recognized by enhanced contributions of C(28) 1,12 diol. Freshwater input may also affect the correlation between temperature and the LDI, but relative C(32) 1,15-diol abundances help to identify and correct for these effects. When taking those factors into account, the calibration error of the LDI is 2.4 °C. As a well-defined proxy for temperatures of the warmest seasons, the LDI can unlock important and previously inaccessible paleoclimate information and will thereby substantially improve our understanding of past climate conditions
Species distinctions among closely related strains of Eustigmatophyceae (Stramenopiles) emphasizing ITS2 sequence-structure data: Eustigmatos and Vischeria
No full texthere is an increasing interest in the Eustigmatophyceae, a class of stramenopile microalgae, because they offer a variety of high-value health-beneficial compounds, e.g. polyunsaturated fatty acids (PUFAs), while concomitantly producing high biomass. Clarification of the taxonomy of these organisms at the species level is important in order to achieve reproducible results and constant yields of valuable compounds in their exploitation. Here the distinction of the, so far exclusively, morphologically defined species of the genera Eustigmatos and Vischeria was tested. Distinctions inferred from almost full 18S and ITS2 rRNA as well as plastid-encoded rbcL gene sequences were evaluated following a morphological investigation. The ITS2 secondary-structure-based phylogenies separated independent lineages (species) with long internal branches. This recommends ITS2 as a promising marker for a DNA metabarcoding approach (culture-independent biodiversity assessment). In contrast, the 18S V4 region which is commonly used in metabarcoding was almost invariant, whereas the almost full length sequences distinguished eight groups/types of strains. Monophyly of the species was supported by shared ITS2 secondary structure features, making them distinct from other eustigmatophyte lineages in concordance with phylogenetic analyses. No groups of strains were congruently supported by all three markers. Consequently, the previous distinction of two genera on the basis of morphology cannot be retained and the species should be accommodated in a single genus, Vischeria. Taxonomic changes among the species with the definition of epitypes, on the basis of cryopreserved strains, are recommended. Two findings point to a more complex evolutionary history of the species. The rbcL and nuclear markers resulted in disparate groupings of strains. In three species divergent intragenomic ITS2 paralogues were revealed. Therefore, a still broader taxon sampling, in conjunction with a deep sequencing approach, is needed for a more comprehensive understanding of the complex evolution of eustigmatophyte species
Congruence of chloroplast- and nuclear-encoded DNA sequence variations used to assess species boundaries in the soil microalga Heterococcus (Stramenopiles, Xanthophyceae)
Get PDFBackground: Heterococcus is a microalgal genus of Xanthophyceae (Stramenopiles) that is common and widespread in soils, especially from cold regions. Species are characterized by extensively branched filaments produced when grown on agarized culture medium. Despite the large number of species described exclusively using light microscopic morphology, the assessment of species diversity is hampered by extensive morphological plasticity.
Results: Two independent types of molecular data, the chloroplast-encoded psbA/rbcL spacer complemented by rbcL gene and the internal transcribed spacer 2 of the nuclear rDNA cistron (ITS2), congruently recovered a robust phylogenetic structure. With ITS2 considerable sequence and secondary structure divergence existed among the eight species, but a combined sequence and secondary structure phylogenetic analysis confined to helix II of ITS2 corroborated relationships as inferred from the rbcL gene phylogeny. Intra-genomic divergence of ITS2 sequences was revealed in many strains. The 'monophyletic species concept', appropriate for microalgae without known sexual reproduction, revealed eight different species. Species boundaries established using the molecular-based monophyletic species concept were more conservative than the traditional morphological species concept. Within a species, almost identical chloroplast marker sequences (genotypes) were repeatedly recovered from strains of different origins. At least two species had widespread geographical distributions; however, within a given species, genotypes recovered from Antarctic strains were distinct from those in temperate habitats. Furthermore, the sequence diversity may correspond to adaptation to different types of habitats or climates.
Conclusions: We established a method and a reference data base for the unambiguous identification of species of the common soil microalgal genus Heterococcus which uses DNA sequence variation in markers from plastid and nuclear genomes. The molecular data were more reliable and more conservative than morphological data
Screening of microalgae and cyanobacteria strains for α-tocopherol content at different growth phases and the influence of nitrate reduction on α-tocopherol production
No full textBiotechnological Screening of Microalgal and Cyanobacterial Strains for Biogas Production and Antibacterial and Antifungal Effects
No full textMicroalgae and cyanobacteria represent a valuable natural resource for the generation of a large variety of chemical substances that are of interest for medical research, can be used as additives in cosmetics and food production, or as an energy source in biogas plants. The variety of potential agents and the use of microalgae and cyanobacteria biomass for the production of these substances are little investigated and not exploited for the market. Due to the enormous biodiversity of microalgae and cyanobacteria, they hold great promise for novel products. In this study, we investigated a large number of microalgal and cyanobacterial strains from the Culture Collection of Algae at Göttingen University (SAG) with regard to their biomass and biogas production, as well antibacterial and antifungal effects. Our results demonstrated that microalgae and cyanobacteria are able to generate a large number of economically-interesting substances in different quantities dependent on strain type. The distribution and quantity of some of these components were found to reflect phylogenetic relationships at the level of classes. In addition, between closely related species and even among multiple isolates of the same species, the productivity may be rather variable
TESTING FOR SPECIES AND GENUS CONCEPTS AND ENDEMISM IN FILAMENTOUS XANTHOPHYCEAE (STRAMEOPILES)
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