Possible effects of global environmental changes on Antarctic benthos: a synthesis across five major taxa

Because of the unique conditions that exist around the Antarctic continent, Southern Ocean (SO) ecosystems are very susceptible to the growing impact of global climate change and other anthropogenic influences. Consequently, there is an urgent need to understand how SO marine life will cope with expected future changes in the environment. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity to environmental shifts, making it difficult to predict overall community or ecosystem responses. This emphasizes the need for an improved understanding of the Antarctic benthic ecosystem response to global climate change using a multitaxon approach with consideration of different levels of biological organization. Here, we provide a synthesis of the ability of five important Antarctic benthic taxa (Foraminifera, Nematoda, Amphipoda, Isopoda, and Echinoidea) to cope with changes in the environment (temperature, pH, ice cover, ice scouring, food quantity, and quality) that are linked to climatic changes. Responses from individual to the taxon-specific community level to these drivers will vary with taxon but will include local species extinctions, invasions of warmer-water species, shifts in diversity, dominance, and trophic group composition, all with likely consequences for ecosystem functioning. Limitations in our current knowledge and understanding of climate change effects on the different levels are discussed.     

Complementary neuronal and glial expression of two high-affinity glutamate transporter GLT1/EAAT2 forms in rat cerebral cortex

The glutamate transporter GLT1 is essential in limiting transmitter signaling and restricting harmful receptor overstimulation. It has been shown recently that GLT1 exists in two forms, the generic GLT1 and a 3'-end-spliced variant of GLT1 (GLT1v), both with similar transport characteristics. To differentiate clearly the cellular distribution of both GLT1 forms in the cortex, specific cRNA probes for non-radioactive in situ hybridization were generated and applied to adult rat brain sections. The results were complemented by western and northern blot analyses and by immunocytochemical investigations using specific peptide antibodies against both GLT1 forms. The study confirmed that generic GLT1 mRNA was expressed predominantly in astrocytes and, to a small extent, in neurons, whereas GLT1 protein was detected only in cell membranes of astrocytes. On the other hand, GLT1v mRNA and protein were demonstrated predominantly in neurons and in non-astrocytic glial cells irrespective of the cortical areas studied. A cytoplasmic granular staining of neurons and astrocytes predominated in the demonstration of GLT1v protein. It is concluded that the cellular expression of the two GLT1 forms is complementary. The cytoplasmic vesicular distribution of GLT1v may represent an endogenous protective mechanism to limit glutamate-induced excitotoxicity.     

Germline integration of moloney murine leukemia virus at the Mov13 locus leads to recessive lethal mutation and early embryonic death

Thirteen mouse substrains genetically transmitting the exogenous Moloney murine leukemia virus (M-MuLV) at a single locus (Mov locus) have been derived previously. Experiments were performed to investigate whether homozygosity at the Mov loci would be compatible with normal development. Animals heterozygous at an Mov locus were mated, and the genotype of the offspring was analyzed. From parents heterozygous at the loci Mov1 to Mov12, respectively, homozygous offspring were obtained with the expected Mendelian frequency. In contrast, no homozygous offspring or embryos older than day 15 of gestation were obtained from parents heterozygous at the Mov13 locus. When pregnant Mov13 females at day 13 and day 14 of gestation were analyzed, approximately 25% of the embryos were degenerated. Genotyping revealed that these degenerated embryos were invariably homozygous and the normal appearing embryos were either heterozygous or negative for M-MuLV. These results suggest that integration of M-MuLV at the Mov13 locus leads to insertion mutagenesis, resulting in embryonic arrest between day 12 and day 13 of gestation. It is possible that the Mov13 locus represents a gene or gene complex involved in the early embryonic development of the mouse.     

First detection of the microsporidium Enterocytozoon bieneusi in non-mammalian hosts (chickens)

Faecal samples taken from eight underweight, approximately 5-week-old broiler chickens in a poultry abattoir were investigated for microsporidial infections by light microscopy, electron microscopy, and PCR. In two of six chickens, which were suspected of being infected with microsporidia by light microscopy, Enterocytozoon bieneusi (genotype 'J') was detected by PCR and DNA sequencing, and in one of the two PCR-positive samples by extensive electron microscopy. This is the first time that E. bieneusi has been detected in chickens, i.e. in a non-mammalian species.     

Focal DNA Copy Number Changes in Neuroblastoma Target MYCN Regulated Genes

Neuroblastoma is an embryonic tumor arising from immature sympathetic nervous system cells. Recurrent genomic alterations include MYCN and ALK amplification as well as recurrent patterns of gains and losses of whole or large partial chromosome segments. A recent whole genome sequencing effort yielded no frequently recurring mutations in genes other than those affecting ALK. However, the study further stresses the importance of DNA copy number alterations in this disease, in particular for genes implicated in neuritogenesis. Here we provide additional evidence for the importance of focal DNA copy number gains and losses, which are predominantly observed in MYCN amplified tumors. A focal 5 kb gain encompassing the MYCN regulated miR-17∼92 cluster as sole gene was detected in a neuroblastoma cell line and further analyses of the array CGH data set demonstrated enrichment for other MYCN target genes in focal gains and amplifications. Next we applied an integrated genomics analysis to prioritize MYCN down regulated genes mediated by MYCN driven miRNAs within regions of focal heterozygous or homozygous deletion. We identified RGS5, a negative regulator of G-protein signaling implicated in vascular normalization, invasion and metastasis, targeted by a focal homozygous deletion, as a new MYCN target gene, down regulated through MYCN activated miRNAs. In addition, we expand the miR-17∼92 regulatory network controlling TGFß signaling in neuroblastoma with the ring finger protein 11 encoding gene RNF11, which was previously shown to be targeted by the miR-17∼92 member miR-19b. Taken together, our data indicate that focal DNA copy number imbalances in neuroblastoma (1) target genes that are implicated in MYCN signaling, possibly selected to reinforce MYCN oncogene addiction and (2) serve as a resource for identifying new molecular targets for treatment.     

The challenge of estimating kelp production in a turbid marine environment

Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (K_d) between 0.28 and 0.87 m⁻¹. Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted K_d to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3–4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m⁻² seafloor · d⁻¹ for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.     

Heterologous expression of the glutamine transporter SNAT3 in Xenopus oocytes is associated with four modes of uncoupled transport

The glutamine transporter SNAT3 (SLC38A3, former SN1) plays a major role in glutamine release from brain astrocytes and in glutamine uptake into hepatocytes and kidney epithelial cells. Here we expressed rat SNAT3 in oocytes of Xenopus laevis and reinvestigated its transport modes using two-electrode voltage clamp and pH-sensitive microelectrodes. In addition to the established coupled Na+-glutamine-cotransport/H+ antiport, we found that there are three conductances associated with SNAT3, two dependent and one independent of the amino acid substrate. The glutamine-dependent conductance is carried by cations at pH 7.4, whereas at pH 8.4 the inward currents are still dependent on the presence of external Na+ but are carried by H+. Mutation of threonine 380 to alanine abolishes the cation conductance but leaves the proton conductance intact. Under Na+-free conditions, where the substrate-dependent conductance is suppressed, a substrate-independent, outwardly rectifying current becomes apparent at pH 8.4 that is carried by K+ and H+. In addition, we identified a glutamine-dependent uncoupled Na+/H+ exchange activity that becomes apparent upon removal of Na+ in the presence of glutamine. In conclusion, our results suggest that, in addition to coupled transport, SNAT3 mediates four modes of uncoupled ion movement across the membrane.     

Microarray and functional gene analyses of sulfate-reducing prokaryotes in low-sulfate, acidic fens reveal cooccurrence of recognized genera and novel lineages

Low-sulfate, acidic (approximately pH 4) fens in the Lehstenbach catchment in the Fichtelgebirge mountains in Germany are unusual habitats for sulfate-reducing prokaryotes (SRPs) that have been postulated to facilitate the retention of sulfur and protons in these ecosystems. Despite the low in situ availability of sulfate (concentration in the soil solution, 20 to 200 μM) and the acidic conditions (soil and soil solution pHs, approximately 4 and 5, respectively), the upper peat layers of the soils from two fens (Schlöppnerbrunnen I and II) of this catchment displayed significant sulfate-reducing capacities. 16S rRNA gene-based oligonucleotide microarray analyses revealed stable diversity patterns for recognized SRPs in the upper 30 cm of both fens. Members of the family “Syntrophobacteraceae” were detected in both fens, while signals specific for the genus Desulfomonile were observed only in soils from Schlöppnerbrunnen I. These results were confirmed and extended by comparative analyses of environmentally retrieved 16S rRNA and dissimilatory (bi)sulfite reductase (dsrAB) gene sequences; dsrAB sequences from Desulfobacca-like SRPs, which were not identified by microarray analysis, were obtained from both fens. Hypotheses concerning the ecophysiological role of these three SRP groups in the fens were formulated based on the known physiological properties of their cultured relatives. In addition to these recognized SRP lineages, six novel dsrAB types that were phylogenetically unrelated to all known SRPs were detected in the fens. These dsrAB sequences had no features indicative of pseudogenes and likely represent novel, deeply branching, sulfate- or sulfite-reducing prokaryotes that are specialized colonists of low-sulfate habitats.The dissimilatory reduction of sulfate is carried out exclusively by prokaryotic organisms and is one of the most important mineralization processes in anoxic aquatic environments, especially marine sediments (29, 30). In contrast to well-studied sulfate-reducing communities in marine (18, 19, 38, 41, 53, 56, 57, 72) and freshwater habitats (39, 40, 59, 60), relatively little is known about the distribution, diversity, and in situ activities of sulfate-reducing prokaryotes (SRPs) in terrestrial ecosystems. The contribution of terrestrial SRPs to the overall turnover of organic matter is likely of minor importance on a global scale. However, SRPs contribute to the biodegradation of pollutants in soils and subsurface environments (1, 15, 49, 71) and are important to the geomicrobiology of specialized terrestrial habitats that are subject to flooding, such as rice fields (68, 76, 77) and fens (3, 5).δ³⁴S values and ³⁵S-labeling patterns indicate that the dissimilatory reduction of sulfate is an ongoing process in the acidic fens of a forested catchment in northern Bavaria, Germany (Lehstenbach, Fichtelgebirge) (3, 5). The deposition of sulfur that originated from the combustion of soft coal in Eastern Europe (10) led to accumulation of sulfur in the soils of this catchment (4). Although pollution controls have lessened the deposition in recent years, desorption of sulfate in aerated upland soils causes sulfate to enter fens at lower elevations. It was hypothesized that the dissimilatory reduction of sulfate in these mainly anoxic, waterlogged acidic fen soils (the pH of the fen soils is approximately 4) contributes to the retention of sulfur in this ecosystem (3, 4, 50). The reduction of sulfate in these fens is also a sink for protons and thus decreases the acidity of the soil solution and groundwater of this habitat.The acidity and low sulfate content of some of the fens in the Lehstenbach catchment provide an unusual habitat for SRPs, and the occurrence and activity of these organisms in such habitats have received little attention. The main objectives of this study were (i) to assess the capacity of the fen soils to reduce sulfate along vertical soil profiles in the upper peat layers, (ii) to determine the vertical community profiles for all known SRP lineages that inhabit the fens by the use of a 16S rRNA-based oligonucleotide microarray (SRP-PhyloChip) (44), (iii) to resolve the possible existence of novel SRP lineages in the fens by retrieval of dsrAB, which are genes that encode the alpha and beta subunits of the siroheme dissimilatory (bi)sulfite reductase (EC 1.8.99.3) (34, 66, 74), and (iv) to deduce the possible in situ functional relationships that can be inferred from this collective information.     

Is Shade Beneficial for Mediterranean Shrubs Experiencing Periods of Extreme Drought and Late-winter Frosts?

Background and Aims

Plants are naturally exposed to multiple, frequently interactive stress factors, most of which are becoming more severe due to global change. Established plants have been reported to facilitate the establishment of juvenile plants, but net effects of plant–plant interactions are difficult to assess due to complex interactions among environmental factors. An investigation was carried out in order to determine how two dominant evergreen shrubs (Quercus ilex and Arctostaphylos uva-ursi) co-occurring in continental, Mediterranean habitats respond to multiple abiotic stresses and whether the shaded understorey conditions ameliorate the negative effects of drought and winter frosts on the physiology of leaves.

Methods

Microclimate and ecophysiology of sun and shade plants were studied at a continental plateau in central Spain during 2004–2005, with 2005 being one of the driest and hottest years on record; several late-winter frosts also occurred in 2005.

Key Results

Daytime air temperature and vapour pressure deficit were lower in the shade than in the sun, but soil moisture was also lower in the shade during the spring and summer of 2005, and night-time temperatures were higher in the shade. Water potential, photochemical efficiency, light-saturated photosynthesis, stomatal conductance and leaf ¹³C composition differed between sun and shade individuals throughout the seasons, but differences were species specific. Shade was beneficial for leaf-level physiology in Q. ilex during winter, detrimental during spring for both species, and of little consequence in summer.

Conclusions

The results suggest that beneficial effects of shade can be eclipsed by reduced soil moisture during dry years, which are expected to be more frequent in the most likely climate change scenarios for the Mediterranean region.Key words: Frost, climate change, shade, drought, plant–plant interactions, Quercus ilex, Arctostaphylos uva-ursi, soil moisture, facilitation