Effects of UV radiation on the structure of Arctic macrobenthic communities

At present, information on the effects of ultraviolet radiation (UVR) on structure and diversity of polar, in particular Arctic, benthic communities is scarce. It is unclear whether and to what extent communities of different successional age are susceptible to UVR and whether UVR effects known to be detrimental at the species level can be buffered at the community level. In a subtidal field study on Spitsbergen (Norwegian Arctic), we investigated the potential effect of distinct UVR regimes on macrobenthic communities of different successional ages, grown on ceramic tiles. Total taxon cover, taxon composition, evenness, and richness were assessed after experimental exposure of 4 and 8 weeks. Overall, 17 algal and invertebrate taxa were encountered in the study and diatoms dominated the communities regardless of successional age or radiation treatment. UVR effects were dependent on both exposure time and community age. We did not find overall detrimental UVB effects. In contrast, abundance of several species increased in UVR-exposed communities. Especially, UVA seemed to have a beneficial effect in that several green and brown algal taxa increased in abundance (e.g. Ulothrix flacca, Chlorophyta, and Desmarestia sp., Phaeophyceae). In general, UVR effects depended on species composition and thus on successional age of communities, with later successional communities likely to be able to buffer and alleviate possible negative effects of UVR at species level. Overall, the presented study provides a first insight into the complex role UVR plays in structuring Arctic epibenthic communities.     

Responses of Antarctic Iridaea cordata (Rhodophyta) tetraspores exposed to ultraviolet radiation

In Antarctica ozone depletion is highest during spring, coinciding with the reproduction of many seaweed species. Propagules are the life-stage of an alga most susceptible to environmental perturbations. Therefore, fertile thalli of Iridaea cordata (Turner) Bory (Rhodophyta) were collected in the eulittoral of King George Island (Antarctica) to examine spore susceptibility to ultraviolet radiation (UVR). In the laboratory, freshly released tetraspores were exposed to photosynthetically active radiation (PAR) (400–700 nm), PAR+UV-A (320–700 nm) or PAR+UV-A+UV-B (280–700 nm). Photosynthetic efficiency was measured during 1–8 h of exposure and after 48 h of recovery. Additionally, mycosporine-like amino acids (MAAs) and DNA damage were determined. Saturating irradiance of photosynthesis of freshly released tetraspores was 57 µmol photons m⁻² s⁻¹. Exposure to increasing fluence of PAR reduced photosynthetic efficiency. UVR further decreased the photosynthetic efficiencies of the tetraspores but spores were able to recover completely after UVR exposure and 2 days post-cultivation under low PAR. DNA damage was minimal and lesions were effectively repaired under photoreactivating light. Concentrations of the MAAs shinorine and palythine were higher in tetraspores treated with UVR than in spores only exposed to PAR. Generally, the tetraspores show a good UV tolerance. This flexible response of the tetraspores of this species to changing radiation conditions enables the alga to grow along a considerable depth gradient from the sublittoral to the eulittoral where they can be exposed to enhanced UVBR under conditions of stratospheric ozone depletion.     

Blood-based profiles of DNA methylation predict the underlying distribution of cell types

The potential influence of underlying differences in relative leukocyte distributions in studies involving blood-based profiling of DNA methylation is well recognized and has prompted development of a set of statistical methods for inferring changes in the distribution of white blood cells using DNA methylation signatures. However, the extent to which this methodology can accurately predict cell-type proportions based on blood-derived DNA methylation data in a large-scale epigenome-wide association study (EWAS) has yet to be examined. We used publicly available data deposited in the Gene Expression Omnibus (GEO) database (accession number GSE37008), which consisted of both blood-derived epigenome-wide DNA methylation data assayed using the Illumina Infinium HumanMethylation27 BeadArray and complete blood cell (CBC) counts among a community cohort of 94 non-diseased individuals. Constrained projection (CP) was used to obtain predictions of the proportions of lymphocytes, monocytes and granulocytes for each of the study samples based on their DNA methylation signatures. Our findings demonstrated high consistency between the average CBC-derived and predicted percentage of monocytes and lymphocytes (17.9% and 17.6% for monocytes and 82.1% and 81.4% for lymphocytes), with root mean squared error (rMSE) of 5% and 6%, for monocytes and lymphocytes, respectively. Similarly, there was moderate-high correlation between the CP-predicted and CBC-derived percentages of monocytes and lymphocytes (0.60 and 0.61, respectively), and these results were robust to the number of leukocyte differentially methylated regions (L-DMRs) used for CP prediction. These results serve as further validation of the CP approach and highlight the promise of this technique for EWAS where DNA methylation is profiled using whole-blood genomic DNA.     

Effects of ocean acidification on growth and physiology of Ulva lactuca (Chlorophyta) in a rockpool‐scenario

Rising atmospheric CO₂‐concentrations will have severe consequences for a variety of biological processes. We investigated the responses of the green alga Ulva lactuca (Linnaeus) to rising CO₂‐concentrations in a rockpool scenario. U. lactuca was cultured under aeration with air containing either preindustrial pCO₂ (280 μatm) or the pCO₂ predicted by the end of the 21st century (700 μatm) for 31 days. We addressed the following question: Will elevated CO₂‐concentrations affect photosynthesis (net photosynthesis, maximum relative electron transport rate (rETR(max)), maximum quantum yield (Fv/Fm), pigment composition) and growth of U. lactuca in rockpools with limited water exchange? Two phases of the experiment were distinguished: In the initial phase (day 1–4) the Seawater Carbonate System (SWCS) of the culture medium could be adjusted to the selected atmospheric pCO₂ condition by continuous aeration with target pCO₂ values. In the second phase (day 4–31) the SWCS was largely determined by the metabolism of the growing U. lactuca biomass. In the initial phase, Fv/Fm and rETR(max) were only slightly elevated at high CO₂‐concentrations, whereas growth was significantly enhanced. After 31 days the Chl a content of the thalli was significantly lower under future conditions and the photosynthesis of thalli grown under preindustrial conditions was not dependent on external carbonic anhydrase. Biomass increased significantly at high CO₂‐concentrations. At low CO₂‐concentrations most adult thalli disintegrated between day 14 and 21, whereas at high CO₂‐concentrations most thalli remained integer until day 31. Thallus disintegration at low CO₂‐concentrations was mirrored by a drastic decline in seawater dissolved inorganic carbon and HCO₃^?. Accordingly, the SWCS differed significantly between the treatments. Our results indicated a slight enhancement of photosynthetic performance and significantly elevated growth of U. lactuca at future CO₂‐concentrations. The accelerated thallus disintegration at high CO₂‐concentrations under conditions of limited water exchange indicates additional CO₂ effects on the life cycle of U. lactuca when living in rockpools.     

The DNA methylation profile of activated human natural killer cells

Natural killer (NK) cells are now recognized to exhibit characteristics akin to cells of the adaptive immune system. The generation of adaptive memory is linked to epigenetic reprogramming including alterations in DNA methylation. The study herein found reproducible genome wide DNA methylation changes associated with human NK cell activation. Activation led predominately to CpG hypomethylation (81% of significant loci). Bioinformatics analysis confirmed that non-coding and gene-associated differentially methylated sites (DMS) are enriched for immune related functions (i.e., immune cell activation). Known DNA methylation-regulated immune loci were also identified in activated NK cells (e.g., TNFA, LTA, IL13, CSF2). Twenty-one loci were designated high priority and further investigated as potential markers of NK activation. BHLHE40 was identified as a viable candidate for which a droplet digital PCR assay for demethylation was developed. The assay revealed high demethylation in activated NK cells and low demethylation in naïve NK, T- and B-cells. We conclude the NK cell methylome is plastic with potential for remodeling. The differentially methylated region signature of activated NKs revealed similarities with T cell activation, but also provided unique biomarker candidates of NK activation, which could be useful in epigenome-wide association studies to interrogate the role of NK subtypes in global methylation changes associated with exposures and/or disease states.     

Effects of ultraviolet radiation on photosynthesis and related enzyme reactions of marine macroalgae

 Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen (Monostroma arcticum, Laminaria solidungula, Alaria esculenta, Palmaria palmata, Phycodrys rubens) during a 72-h exposure to UV radiation. Maximal quantum yield of photochemistry (Fv/Fm) and maximal electron transport rate (ETRmax) were measured with a pulse-amplitude-modulated fluorometer; the activity of the Calvin cycle enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric test. Proteins of crude extracts were separated by SDS gel electrophoresis and changes in cellular concentrations of Rubisco were determined. Moreover, the concentration of chlorophyll a (Chl a), and protein content, were measured photometrically. In all species, Chl a content, maximal quantum yield as well as ETRmax decreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gels showed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradation of the enzyme. However, in A. esculenta, the formation of a high-molecular-weight polypeptide was observed. In all species, the activity of Rubisco was more strongly impaired than that of G3PDH. Exposure to UV resulted in loss of total protein only in the deepwater species L. solidungula and P. rubens. The different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field. Received: 4 October 1999 / Accepted: 15 February 2000     

pEffects of UV radiation on the ultrastructure of several red algae

The effect of ultraviolet (UV) radiation on the ultrastructure of four red algae, the endemic Antarctic Palmaria decipiens (Reinsch) Ricker and Phycodrys austrogeorgica Skottsberg, the Arctic‐cold temperate Palmaria palmata (Linnaeus) O. Kuntze and the cosmopolitan Bangia atropurpurea (Roth) C. Agardh was studied. All four species showed a formation of ‘inside‐out’ vesicles from the chloroplast thylakoids upon exposure to artificial UV‐radiation. In P. decipiens, most vesicles were developed after 8 h and in P. palmata, after 48 h of UV exposure. In B. atropurpurea, vesi‐culation of thylakoids was observed after 72 h of UV irradiation. In Ph. austrogeorgica, the chloroplast envelope and thylakoid membranes were damaged and the phycobilisomes became detached from the thylakoids after 12 h of UV exposure. Ultraviolet‐induced changes in the membrane structure of mitochondria were observed in P. decipiens and P. palmata. However, in P. decipiens they were reversible as was the damage in chloroplast fine structure after 12 h of UV treatment. Protein crystals in Ph. austrogeorgica showed degradation after exposure to UV radiation. Different methods of fixation and embedding macroalgal material are discussed. These findings give insight into the fine structural changes which occur during and after UV exposure and indicate a relationship between the species dependent sensitivity to UV‐exposure and the depth distribution of the different species.     

Two forms of phycobilisomes in the Antarctic red macroalga Palmaria decipiens (Palmariales, Florideophyceae)

The phycobilisomes (PBS), the light-harvesting antennae, from the endemic Antarctic red macroalga Palmaria decipiens were isolated on discontinuous sucrose gradients in two discrete bands and not in one as expected. To exclude methodical faults, we also isolated PBS from the temperate Palmaria palmata and the unicellular red algae Porphyridium cruentum and Rhodella violacea . In P. palmata the PBS were separated in two discrete bands, whereas the PBS from Porphyridium and Rhodella were found in one band. The double-banded PBS (PBS_up and PBS_low) from P. decipiens were further characterized by absorption and fluorescence spectroscopy, native and SDS-PAGE as well as by negative staining. The phycobiliproteins RIII-phycoerythrin, RI-phycocyanin and allophycocyanin were identified and 3 γ -subunits were described. The PBS_up and PBS_low showed no significant differences in their absorption spectra and phycobiliprotein ratios although the negative stained PBS_low were smaller. Differences were found in their low molecular mass subunit complexes, which are assumed to be r-phycoerythrin. The polypeptide pattern of the PBS_up and PBS_low showed no differences in the molecular masses of their subunits and linker polypeptides, but in their percentage distribution. The results suggest that the PBS_low is a closer packed and PBS_up a little more loosely aggregated hemiellipsiodal PBS form. We discuss the ecophysiological function of two PBS forms in P. decipiens and suggest advantages in the rapid acclimation to changes in environmental light conditions.