Smallest Algae Thrive As the Arctic Ocean Freshens Li, William K.W; McLaughlin, Fiona A; Lovejoy, Connie ...
Science (American Association for the Advancement of Science),
10/2009, Letnik:
326, Številka:
5952
Journal Article
Recenzirano
As climate changes and the upper Arctic Ocean receives more heat and fresh water, it becomes more difficult for mixing processes to deliver nutrients from depth to the surface for phytoplankton ...growth. Competitive advantage will presumably accrue to small cells because they are more effective in acquiring nutrients and less susceptible to gravitational settling than large cells. Since 2004, we have discerned an increase in the smallest algae and bacteria along with a concomitant decrease in somewhat larger algae. If this trend toward a community of smaller cells is sustained, it may lead to reduced biological production at higher trophic levels.
The Cyanobacteria Prochlorococcus and Synechococcus account for a substantial fraction of marine primary production. Here, we present quantitative niche models for these lineages that assess present ...and future global abundances and distributions. These niche models are the result of neural network, nonparametric, and parametric analyses, and they rely on >35,000 discrete observations from all major ocean regions. The models assess cell abundance based on temperature and photosynthetically active radiation, but the individual responses to these environmental variables differ for each lineage. The models estimate global biogeographic patterns and seasonal variability of cell abundance, with maxima in the warm oligotrophic gyres of the Indian and the western Pacific Oceans and minima at higher latitudes. The annual mean global abundances of Prochlorococcus and Synechococcus are 2.9 ± 0.1 × 10 ²⁷ and 7.0 ± 0.3 × 10 ²⁶ cells, respectively. Using projections of sea surface temperature as a result of increased concentration of greenhouse gases at the end of the 21st century, our niche models projected increases in cell numbers of 29% and 14% for Prochlorococcus and Synechococcus , respectively. The changes are geographically uneven but include an increase in area. Thus, our global niche models suggest that oceanic microbial communities will experience complex changes as a result of projected future climate conditions. Because of the high abundances and contributions to primary production of Prochlorococcus and Synechococcus , these changes may have large impacts on ocean ecosystems and biogeochemical cycles.
Increasing global temperatures are having a profound impact in the Arctic, including the dramatic loss of multiyear sea ice in 2007 that has continued to the present. The majority of life in the ...Arctic is microbial and the consequences of climate-mediated changes on microbial marine food webs, which are responsible for biogeochemical cycling and support higher trophic levels, are unknown. We examined microbial communities over time by using high-throughput sequencing of microbial DNA collected between 2003 and 2010 from the subsurface chlorophyll maximum (SCM) layer of the Beaufort Sea (Canadian Arctic). We found that overall this layer has freshened and concentrations of nitrate, the limiting nutrient for photosynthetic production in Arctic seas, have decreased. We compared microbial communities from before and after the record September 2007 sea ice minimum and detected significant differences in communities from all three domains of life. In particular, there were significant changes in species composition of Eukarya, with ciliates becoming more common and heterotrophic marine stramenopiles (MASTs) accounting for a smaller proportion of sequences retrieved after 2007. Within the Archaea, Marine Group I Thaumarchaeota, which earlier represented up to 60% of the Archaea sequences in this layer, have declined to <10%. Bacterial communities overall were less diverse after 2007, with a significant decrease of the Bacteroidetes. These significant shifts suggest that the microbial food webs are sensitive to physical oceanographic changes such as those occurring in the Canadian Arctic over the past decade.
The macroecological relationships among marine phytoplankton total cell density, community size structure and temperature have lacked a theoretical explanation. The tiniest members of this planktonic ...group comprise cyanobacteria and eukaryotic algae smaller than 2 μm in diameter, collectively known as picophytoplankton. We combine here two ecological rules, the temperature–size relationship with the allometric size‐scaling of population abundance to explain a remarkably consistent pattern of increasing picophytoplankton biomass with temperature over the −0.6 to 22 °C range in a merged dataset obtained in the eastern and western temperate North Atlantic Ocean across a diverse range of environmental conditions. Our results show that temperature alone was able to explain 73% of the variance in the relative contribution of small cells to total phytoplankton biomass regardless of differences in trophic status or inorganic nutrient loading. Our analysis predicts a gradual shift toward smaller primary producers in a warmer ocean. Because the fate of photosynthesized organic carbon largely depends on phytoplankton size, we anticipate future alterations in the functioning of oceanic ecosystems.
Massively parallel sequencing of DNA molecules in the plasma of pregnant women has been shown to allow accurate and noninvasive prenatal detection of fetal trisomy 21. However, whether the sequencing ...approach is as accurate for the noninvasive prenatal diagnosis of trisomy 13 and 18 is unclear due to the lack of data from a large sample set. We studied 392 pregnancies, among which 25 involved a trisomy 13 fetus and 37 involved a trisomy 18 fetus, by massively parallel sequencing. By using our previously reported standard z-score approach, we demonstrated that this approach could identify 36.0% and 73.0% of trisomy 13 and 18 at specificities of 92.4% and 97.2%, respectively. We aimed to improve the detection of trisomy 13 and 18 by using a non-repeat-masked reference human genome instead of a repeat-masked one to increase the number of aligned sequence reads for each sample. We then applied a bioinformatics approach to correct GC content bias in the sequencing data. With these measures, we detected all (25 out of 25) trisomy 13 fetuses at a specificity of 98.9% (261 out of 264 non-trisomy 13 cases), and 91.9% (34 out of 37) of the trisomy 18 fetuses at 98.0% specificity (247 out of 252 non-trisomy 18 cases). These data indicate that with appropriate bioinformatics analysis, noninvasive prenatal diagnosis of trisomy 13 and trisomy 18 by maternal plasma DNA sequencing is achievable.
The discovery of epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) has led to unprecedented clinical response in a subset of lung cancer patients carrying the sensitizing EGFR ...mutations (L858R or exon 19 deletion). However, disease progression invariably occurs within a year after the initial TKI treatment, predominantly due to the development of acquired resistance caused by the secondary EGFR T790 M mutation. Numerous second generation irreversible and third generation EGFR T790 M selective EGFR TKIs have been developed to overcome resistance. Besides developing new EGFR TKIs, combination therapy represents another promising strategy to combat resistance. This approach aims at circumventing drug resistance through a so-called bypass signaling mechanism by targeting horizontal pathways or vertical pathways or both. The logical combinations of different molecular targeted drugs inhibiting various oncogenic signaling have been studied. On the other hand, the repurposing of drugs with indications other than oncology has also emerged as a promising approach. In this review, we focus on the effectiveness of combination therapy of EGFR-TKIs with different agents in advanced lung cancer.
•Drug combination represents a promising strategy to combat resistance to EGFR TKIs.•Molecular targeted anticancer drugs can be combined to circumvent drug resistance.•Drug for other indications can also be repurposed to combat resistance to EGFR TKIs.•Drug combinations target horizontal and/or vertical pathways to overcome resistance.•Beneficial combination effect was only observed in specific cancer population.
A central challenge in nanotechnology is the parallel fabrication of complex geometries for nanodevices. Here we report a general method for arranging single-walled carbon nanotubes in two dimensions ...using DNA origami-a technique in which a long single strand of DNA is folded into a predetermined shape. We synthesize rectangular origami templates ( approximately 75 nm x 95 nm) that display two lines of single-stranded DNA 'hooks' in a cross pattern with approximately 6 nm resolution. The perpendicular lines of hooks serve as sequence-specific binding sites for two types of nanotubes, each functionalized non-covalently with a distinct DNA linker molecule. The hook-binding domain of each linker is protected to ensure efficient hybridization. When origami templates and DNA-functionalized nanotubes are mixed, strand displacement-mediated deprotection and binding aligns the nanotubes into cross-junctions. Of several cross-junctions synthesized by this method, one demonstrated stable field-effect transistor-like behaviour. In such organizations of electronic components, DNA origami serves as a programmable nanobreadboard; thus, DNA origami may allow the rapid prototyping of complex nanotube-based structures.
Breast cancer (BC) is the most common malignancy in women. It is classified into a few major molecular subtypes according to hormone and growth factor receptor expression. Over the past few years, ...substantial advances have been made in the discovery of new drugs for treating BC. Improved understanding of the biologic heterogeneity of BC has allowed the development of more effective and individualized approach to treatment. In this review, we provide an update about the current treatment strategy and discuss the various emerging novel therapies for the major molecular subtypes of BC. A brief account of the clinical development of inhibitors of poly(ADP-ribose) polymerase, cyclin-dependent kinases 4 and 6, phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin pathway, histone deacetylation, multi-targeting tyrosine kinases, and immune checkpoints for personalized treatment of BC is included. However, no targeted drug has been approved for the most aggressive subtype-triple negative breast cancer (TNBC). Thus, we discuss the heterogeneity of TNBC and how molecular subtyping of TNBC may help drug discovery for this deadly disease. The emergence of drug resistance also poses threat to the successful development of targeted therapy in various molecular subtypes of BC. New clinical trials should incorporate advanced methods to identify changes induced by drug treatment, which may be associated with the upregulation of compensatory signaling pathways in drug resistant cancer cells.
Sleep disruption is a prevalent symptom reported by survivors of childhood cancer. However, there is no validated instrument for assessing this symptom in this population group. To bridge the ...literature gap, this study translated and adapted the Pittsburgh Sleep Quality Index (PSQI) for Hong Kong Chinese cancer survivors and examined its psychometric properties and factor structure. A convenience sample of 402 Hong Kong Chinese childhood cancer survivors aged 6-18 years were asked to complete the Chinese version of the PSQI, Center for Epidemiologic Studies Depression Scale for Children (CES-DC), Fatigue Scale-Child (FS-C)/Fatigue Scale-Adolescent (FS-A), and Pediatric Quality of Life Inventory (PedsQL). To assess known-group validity, 50 pediatric cancer patients and 50 healthy counterparts were recruited. A sample of 40 children were invited to respond by phone to the PSQI 2 weeks later to assess test-retest reliability. A cutoff score for the translated PSQI used with the survivors was determined using receiver operating characteristic analysis. The Chinese version of the PSQI had a Cronbach alpha of 0.71, with an intraclass correlation coefficient of 0.90. Childhood cancer survivors showed significantly lower mean PSQI scores than children with cancer, and significantly higher mean scores than healthy counterparts. This reflected that childhood cancer survivors had a better sleep quality than children with cancer, but a poorer sleep quality than healthy counterparts. We observed positive correlations between PSQI and CES-DC scores and between PSQI and FS-A/FS-C scores, but a negative correlation between PSQI and PedsQL scores. The results supported that the Chinese version of the PSQI showed convergent validity. Confirmatory factor analysis showed that the translated PSQI data best fit a three-factor model. The best cutoff score to detect insomnia was 5, with a sensitivity of 0.81 and specificity of 0.70. The Chinese version of the PSQI is a reliable and valid instrument to assess subjective sleep quality among Hong Kong Chinese childhood cancer survivors. The validated PSQI could be used in clinical settings to provide early assessments for sleep disruption. Appropriate interventions can therefore be provided to minimize its associated long-term healthcare cost.
Steels represent the most widely-used metallic alloy, possessing a wide range of microstructures and mechanical properties. By examining the mechanical properties of steels in conjunction with ...microstructure this book provides a valuable description of the development and behavior of these materials, the very foundation of their widespread use. Updated throughout and including new chapters on nanostructured steels, and new alloys and technologies for the energy and automobile industries, the book is clearly written and illustrated, with extensive bibliographies and real-life examples. This is an essential reference, both compact and readily comprehensive, for metallurgists and engineers, as well as senior undergraduate students and postgraduates in materials science, physical metallurgy and mechanical engineering.
PDF
