Valve and seta (spine) morphogenesis in the centric diatomChaetoceros peruvianus Brightwell

Summary InChaetoceros peruvianus, the two very long, delicately tapered setae (spine-like processes) of the lower valve curve downwards gently until they are often almost parallel, while those emerging from the upper valve curve sharply downwards until oriented almost in the same direction as the setae of the lower valve. This curvature creates a deep pit between the bases of the upper valve's setae, where they emerge from the valve. In live cells, extension of setae is rapid and very sensitive to disturbance. After cleavage the new silica deposition vesicle (SDV) appears in the centre of the furrow and expands outwards over it. A distinct microtubule centre (MC) appears directly on top of the SDV. Microtubules (MTs) from the MC ensheath the nucleus, and others fan out over the SDV and plasmalemma. A little later, the MC in the lower daughter cell moves off the SDV, and its MTs now appear to mould the plasmalemma/ SDV into the deep pit between the base of the setae. In the upper daughter cell, the MC remains on the SDV. Initiation of setae is first observed as protuberances of bare cytoplasm growing from the sides of the daughter cells, through gaps in the parental valve. Many MTs initially line the plasmalemma of these protuberances as they grow outwards and the SDV also expands over the new surface. As the setae get longer, a unique complex of three organelles appears. Just behind the naked cytoplasm at the tip of the seta, a thin flat layer of fibrous material lines the plasmalemma. This, the first of the complex, is called the thin band. Immediately behind this is the second, a much thicker, denser fibrous band, the thick band. At the front edge of the SDV, 5–6 finger-like outgrowths of silicified wall grow forwards. These are interconnected by the elements of the thick band which thus apparently dictate the polygonal profile of the seta. These also appear to generate the spinules (tiny spines) that adorn the surface of the seta; the spiral pattern of the spinules indicates that this whole complex might differentiate one after the next, in order. Further back from the tip, evenly spaced transverse ribs are formed. These are connected to the third organelle in the complex, the striated band; our interpretation is that the striated band sets up the spacing of the ridges that regularly line the inner surface of the setae. During seta growth, this complex is apparently responsible for controlling the delicate tapering curvature of the very fine silica processes. Since the complex is always seen near the tip of the seta, we conclude that it migrates forwards steadily as the tip grows. While the thin and thick bands could slide continuously over the cell membrane, the striated band must be disassembled and then recycled forward during extension if it is indeed connected to the ridges lining the inside of the setae. We could find no indication that turgor pressure drives extension of the setae, in which event the activity of these organelles is responsible for growth using the justformed silica tube as the base from which extension is generated.     

Responses of epilimnetic phytoplankton to experimental nutrient enrichment in three small seepage lakes

This paper describes the responses of three epilimnetic phytoplanktoncommunities to experimental nitrogen and phosphorus enrichmentas compared to the phytoplankton community in a fourth, unmanipulated,lake. Increased nutrient inputs increased total phytoplanktonbiomass, primary productivity, chlorophytes, cryptomonads andspecies turnover rates in all three enriched lakes; cyanobacteriaincreased in two of the three enriched lakes. However, nutrientaddition also led to declines in previously dominant dinoflagellatesand chrysophytes, and in species diversity. At the species level,there were large changes in community composition from yearto year in both enriched and reference lakes, suggesting thatphytoplankton community composition is highly dynamic even inthe absence of enrichment. Overall, changes in total biomass,productivity and species diversity were consistent among theenriched lakes, while changes in species composition differeddue to variation in the physical, chemical and biotic environmentof each lake. This suggests that aggregated variates are moreuseful for quantitative prediction of nutrient effects, whilespecies responses can be used to signal qualitative differencesin environmental conditions among lakes. ³Present address: Department of Biological Sciences, DartmouthCollege, 6044 Gilman Laboratory, Hanover, NH 03755-3576, USA     

Identifying key biodiversity areas as marine conservation priorities in the greater Caribbean

Increasing rates of Anthropocene biodiversity extinctions suggest a possible sixth mass extinction event. Conservation planners are seeking effective ways to protect species, hotspots of biodiversity, and dynamic ecosystems to reduce and eventually eliminate the degradation and loss of diversity at the scale of genes, species, and ecosystems. While well-established, adequately enforced protected areas (PAs) increase the likelihood of preserving species and habitats, traditional placement methods are frequently inadequate in protecting biodiversity most at risk. Consequently, the Key Biodiversity Area (KBA) Partnership developed a set of science-based criteria and thresholds that iteratively identify sites where biodiversity is most in need of protection. KBA methodology has been rarely applied in the marine realm, where data are often extremely limited. We tested the feasibility of KBA population metrics in the Greater Caribbean marine region using occurrence and population data and threat statuses for 1669 marine vertebrates. These data identified areas where site-specific conservation measures can effectively protect biodiversity. Using KBA criteria pertaining to threatened and irreplaceable biodiversity, we identified 90 geographically unique potential KBAs, 34 outside and 56 within existing PAs. These provide starting points for local conservation managers to verify that KBA thresholds are met and to delineate site boundaries. Significant data gaps, such as population sizes, life history characteristics, and extent of habitats, prevent the full application of the KBA criteria to data-poor marine species. Increasing the rate and scope of marine sampling programs and digital availability of occurrence datasets will improve identification and delineation of KBAs in the marine environment.

     

A novel L-fuco-4-O-methyl-D-glucurono-D-xylan from Hyptis suaveolens

The acidic polysaccharide from the seed-coat mucilage of Hyptis suaveolens is a highly branched L-fuco-4-O-methyl-D-glucurono-D-xylan for which a structure is proposed having a 4-linked beta-D-xylan backbone carrying side chains of single 4-O-methyl-alpha-D-glucuronic acid residues at O-2 and 2-O-L-fucopyranosyl-D-xylopyranose units at O-3. The structural analysis involves base-catalyzed beta-elimination of uronic acid residues from the methylated glycan followed by degradation using a modified Svensson oxidation-elimination sequence.     

The genome sequence of a reassortant bluetongue virus serotype 3 from India

All 10 genome segments (Seg-1 to 10-a total of 19,188 bp) were sequenced from a strain of bluetongue virus serotype 3 (BTV-3) from India (strain IND2003/08). Sequence comparisons showed that nine of the genome segments from this virus group with other eastern topotype strains. Genome Seg-2 and Seg-6 group with eastern BTV-3 strains from Japan. However, Seg-5 (the NS1 gene) from IND2003/08 belongs to a western lineage, demonstrating that IND2003/08 is a reassortant between eastern and western topotype bluetongue viruses. This confirms that western BTV strains have been imported and are circulating within the subcontinent.     

A mouse-adapted SARS-coronavirus causes disease and mortality in BALB/c mice

No single animal model for severe acute respiratory syndrome (SARS) reproduces all aspects of the human disease. Young inbred mice support SARS-coronavirus (SARS-CoV) replication in the respiratory tract and are available in sufficient numbers for statistical evaluation. They are relatively inexpensive and easily accessible, but their use in SARS research is limited because they do not develop illness following infection. Older (12- to 14-mo-old) BALB/c mice develop clinical illness and pneumonitis, but they can be hard to procure, and immune senescence complicates pathogenesis studies. We adapted the SARS-CoV (Urbani strain) by serial passage in the respiratory tract of young BALB/c mice. Fifteen passages resulted in a virus (MA15) that is lethal for mice following intranasal inoculation. Lethality is preceded by rapid and high titer viral replication in lungs, viremia, and dissemination of virus to extrapulmonary sites accompanied by lymphopenia, neutrophilia, and pathological changes in the lungs. Abundant viral antigen is extensively distributed in bronchial epithelial cells and alveolar pneumocytes, and necrotic cellular debris is present in airways and alveoli, with only mild and focal pneumonitis. These observations suggest that mice infected with MA15 die from an overwhelming viral infection with extensive, virally mediated destruction of pneumocytes and ciliated epithelial cells. The MA15 virus has six coding mutations associated with adaptation and increased virulence; when introduced into a recombinant SARS-CoV, these mutations result in a highly virulent and lethal virus (rMA15), duplicating the phenotype of the biologically derived MA15 virus. Intranasal inoculation with MA15 reproduces many aspects of disease seen in severe human cases of SARS. The availability of the MA15 virus will enhance the use of the mouse model for SARS because infection with MA15 causes morbidity, mortality, and pulmonary pathology. This virus will be of value as a stringent challenge in evaluation of the efficacy of vaccines and antivirals.     

Rhizodeposition shapes rhizosphere microbial community structure in organic soil

The aims of the study were to determine group specificity in microbial utilization of root-exudate compounds and whole rhizodeposition; quantify the proportions of carbon acquired by microbial groups from soil organic matter and rhizodeposition, respectively; and assess the importance of root-derived C as a driver of soil microbial community structure. Additions of 13C-labelled root-exudate compounds to organic soil and steady-state labelling of Lolium perenne, coupled to compound-specific isotope ratio mass spectrometry, were used to quantify group-specific microbial utilization of rhizodeposition. Microbial utilization of glucose and fumaric acid was widespread through the microbial community, but glycine was utilized by a narrower range of populations, as indicated by the enrichment of phospholipid fatty acid (PLFA) analysis fractions. In L. perenne rhizospheres, high rates of rhizodeposit utilization by microbial groups showed good correspondence with increased abundance of these groups in the rhizosphere. Although rhizodeposition was not the quantitatively dominant C source for microbes in L. perenne rhizospheres, relative utilization of this C source was an important driver of microbial group abundance in organic soil.     

The recent spread of a vertically transmitted virus through populations of Drosophila melanogaster

The sigma virus is a vertically transmitted pathogen that commonly infects natural populations of Drosophila melanogaster. This virus is the only known host-specific pathogen of D. melanogaster, and so offers a unique opportunity to study the genetics of Drosophila-viral interactions in a natural system. To elucidate the population genetic processes that operate in sigma virus populations, we collected D. melanogaster from 10 populations across three continents. We found that the sigma virus had a prevalence of 0-15% in these populations. Compared to other RNA viruses, we found that levels of viral genetic diversity are very low across Europe and North America. Based on laboratory measurements of the viral substitution rate, we estimate that most European and North American viral isolates shared a common ancestor approximately 200 years ago. We suggest two explanations for this: the first is that D. melanogaster has recently acquired the sigma virus; the second is that a single viral type has recently swept through D. melanogaster populations. Furthermore, in contrast to Drosophila populations, we find that the sigma viral populations are highly structured. This is surprising for a vertically transmitted pathogen that has a similar migration rate to its host. We suggest that the low structure in the viral populations can be explained by the smaller effective population size of the virus.     

Detecting microRNA activity from gene expression data

Background  

MicroRNAs (miRNAs) are non-coding RNAs that regulate gene expression by binding to the messenger RNA (mRNA) of protein coding genes. They control gene expression by either inhibiting translation or inducing mRNA degradation. A number of computational techniques have been developed to identify the targets of miRNAs. In this study we used predicted miRNA-gene interactions to analyse mRNA gene expression microarray data to predict miRNAs associated with particular diseases or conditions.