Cell division in morphological mutants ofAgmenellum quadruplicatum,strain BG-1

Summary Two types of filamentous mutants were derived from the unicellular blue-green alga,Agmenellum, by brief exposure to nitrosoguanidine. The parent exhibits constrictive division analogous to that of the enteric bacteria. The septate mutant exhibits septal division which is almost identical to that observed in all filamentous blue-green algae thus far described. In this mutant, the two outer wall layers fail to invaginate, leaving the daughter cells connected. The coenocytic filamentous mutant divides sporadically by both of these methods. The nuclear region of this mutant appears continuous throughout the length of the filament. It is suggested that the non-septate mutant is impaired in the coordination of cytological events leading to cell division.     

Clustering of the Chemoreceptor Complex in Escherichia coli Is Independent of the Methyltransferase CheR and the Methylesterase CheB

The Escherichia coli chemoreceptors and their associated cytoplasmic proteins, CheA and CheW, cluster predominantly at the cell poles. The nature of the clustering remains a mystery. Recent studies suggest that CheR binding to and/or methylation of the chemoreceptors may play a role in chemoreceptor complex aggregation. In this study, we examined the intracellular distribution of the chemoreceptors by immunoelectron microscopy in strains lacking either the methyltransferase CheR or the methylesterase CheB. The localization data revealed that, in vivo, aggregation of the chemoreceptor complex was independent of either CheR or CheB.     

Multi-scale phylogenetic structure in coastal dune plant communities across the globe

Aims Studies integrating phylogenetic history and large-scale community assembly are few, and many questions remain unanswered. Here, we use a global coastal dune plant data set to uncover the important factors in community assembly across scales from the local filtering processes to the global long-term diversification and dispersal dynamics. Coastal dune plant communities occur worldwide under a wide range of climatic and geologic conditions as well as in all biogeographic regions. However, global patterns in the phylogenetic composition of coastal dune plant communities have not previously been studied.Methods The data set comprised vegetation data from 18463 plots in New Zealand, South Africa, South America, North America and Europe. The phylogenetic tree comprised 2241 plant species from 149 families. We calculated phylogenetic clustering (Net Relatedness Index, NRI, and Nearest Taxon Index, NTI) of regional dune floras to estimate the amount of in situ diversification relative to the global dune species pool and evaluated the relative importance of land and climate barriers for these diversification patterns by geographic analyses of phylogenetic similarity. We then tested whether dune plant communities exhibit similar patterns of phylogenetic structure within regions. Finally, we calculated NRI for local communities relative to the regional species pool and tested for an association with functional traits (plant height and seed mass) thought to vary along sea–inland gradients.Important findings Regional species pools were phylogenetically clustered relative to the global pool, indicating regional diversification. NTI showed stronger clustering than NRI pointing to the importance of especially recent diversifications within regions. The species pools grouped phylogenetically into two clusters on either side of the tropics suggesting greater dispersal rates within hemispheres than between hemispheres. Local NRI plot values confirmed that most communities were also phylogenetically clustered within regions. NRI values decreased with increasing plant height and seed mass, indicating greater phylogenetic clustering in communities with short maximum height and good dispersers prone to wind and tidal disturbance as well as salt spray, consistent with environmental filtering along sea–inland gradients. Height and seed mass both showed significant phylogenetic signal, and NRI tended to correlate negatively with both at the plot level. Low NRI plots tended to represent coastal scrub and forest, whereas high NRI plots tended to represent herb-dominated vegetation. We conclude that regional diversification processes play a role in dune plant community assembly, with convergence in local phylogenetic community structure and local variation in community structure probably reflecting consistent coastal-inland gradients. Our study contributes to a better understanding of the globally distributed dynamic coastal ecosystems and the structuring factors working on dune plant communities across spatial scales and regions.     

Efficacy of immobilized polyplexes and lipoplexes for substrate‐mediated gene delivery

Non‐viral gene delivery by immobilization of complexes to cell‐adhesive biomaterials, a process termed substrate‐mediated delivery, has many in vitro research applications such as transfected cell arrays or models of tissue growth. In this report, we quantitatively investigate the efficiency of gene delivery by surface immobilization, and compare this efficiency to the more typical bolus delivery. The ability to immobilize vectors while allowing cellular internalization is impacted by the biomaterial and vector properties. Thus, to compare this efficiency between vector types and delivery methods, transfection conditions were initially identified that maximized transgene expression. For surface delivery from tissue culture polystyrene, DNA complexes were immobilized to pre‐adsorbed serum proteins prior to cell seeding, while for bolus delivery, complexes were added to the media above adherent cells. Mathematical modeling of vector binding, release, and cell association using a two‐site model indicated that the kinetics of polyplex binding to cells was faster than for lipoplexes, yet both vectors have a half‐life on the surface of approximately 17 min. For bolus and surface delivery, the majority of the DNA in the system remained in solution or on the surface, respectively. For polyplexes, the efficiency of trafficking of cell‐associated polyplexes to the nucleus for surface delivery is similar or less than bolus delivery, suggesting that surface immobilization may decrease the activity of the complex. The efficiency of nuclear association for cell‐associated lipoplexes is similar or greater for surface delivery relative to bolus. These studies suggest that strategies to enhance surface delivery for polyplexes should target the vector design to enhance its potency, whereas enhancing lipoplex delivery should target the material design to increase internalization. Biotechnol. Bioeng. 2009;102: 1679–1691. © 2008 Wiley Periodicals, Inc.     

High-Level Diversity of Tailed Phages,Eukaryote-Associated Viruses,and Virophage-Like Elements in the Metaviromes of Antarctic Soils

The metaviromes of two distinct Antarctic hyperarid desert soil communities have been characterized. Hypolithic communities, cyanobacterium-dominated assemblages situated on the ventral surfaces of quartz pebbles embedded in the desert pavement, showed higher virus diversity than surface soils, which correlated with previous bacterial community studies. Prokaryotic viruses (i.e., phages) represented the largest viral component (particularly Mycobacterium phages) in both habitats, with an identical hierarchical sequence abundance of families of tailed phages (Siphoviridae > Myoviridae > Podoviridae). No archaeal viruses were found. Unexpectedly, cyanophages were poorly represented in both metaviromes and were phylogenetically distant from currently characterized cyanophages. Putative phage genomes were assembled and showed a high level of unaffiliated genes, mostly from hypolithic viruses. Moreover, unusual gene arrangements in which eukaryotic and prokaryotic virus-derived genes were found within identical genome segments were observed. Phycodnaviridae and Mimiviridae viruses were the second-most-abundant taxa and more numerous within open soil. Novel virophage-like sequences (within the Sputnik clade) were identified. These findings highlight high-level virus diversity and novel species discovery potential within Antarctic hyperarid soils and may serve as a starting point for future studies targeting specific viral groups.     

The Defining Moment: Children's Conceptualization of Race and Experiences with Racial Discrimination

This paper examines whether children of marginalized racial/ethnic groups have an awareness of race at earlier ages than youth from non-marginalized groups, documents their experiences with racial discrimination, and utilizes a modified racism-related stress model to explore the relationship between perceived racial discrimination and self-esteem. Data were collected for non-Hispanic black, non-Hispanic white, and Hispanic children aged 7 - 12 using face-to-face interviews (n = 175). The concept of race was measured by assessing whether children could define race, if not a standard definition was provided. Racial discrimination was measured using the Williams Every-day-Discrimination Scale, self-esteem was measured using the Rosenberg Scale, and ethnic identity was assessed using the Multi-group Ethnic Identity Measure. Non-Hispanic black children were able to define race more accurately, but overall, Hispanic children encountered more racial discrimination, with frequent reports of ethnic slurs. Additionally, after accounting for ethnic identity, perceived racial discrimination remained a salient stressor that contributed to low self-esteem.     

Effect of Src kinase phosphorylation on disordered C-terminal domain of N-methyl-D-aspartic acid (NMDA) receptor subunit GluN2B protein

NMDA receptors are ligand-gated ion channels with a regulatory intracellular C-terminal domain (CTD). In GluN2B, the CTD is the largest domain in the protein but is intrinsically disordered. The GluN2B subunit is the major tyrosine-phosphorylated protein in synapses. Src kinase phosphorylates the GluN2B CTD, but it is unknown how this affects channel activity. In disordered proteins, phosphorylation can tip the balance between order and disorder. Transitions can occur in both directions, so it is not currently possible to predict the effects of phosphorylation. We used single molecule fluorescence to characterize the effects of Src phosphorylation on GluN2B. Scanning fluorescent labeling sites throughout the domain showed no positional dependence of the energy transfer. Instead, efficiency only scaled with the separation between labeling sites suggestive of a relatively featureless conformational energy landscape. Src phosphorylation led to a general expansion of the polypeptide, which would result in greater exposure of known protein-binding sites and increase the physical separation between contiguous sites. Phosphorylation makes the CTD more like a random coil leaving open the question of how Src exerts its effects on the NMDA receptor.     

Smaller species experience mild adversity under shading in an old‐field plant community

Plant competition experiments commonly suggest that larger species have an advantage, primarily in terms of light acquisition. However, within crowded natural vegetation, where competition evidently impacts fitness, most resident species are relatively small. It remains unclear, therefore, whether the size advantage observed in controlled experiments is normally realized in habitats where competition is most intense. We characterized the light environment and tested for evidence of a size advantage in competition for light in an old‐field plant community composed of perennial herbaceous species. We investigated whether larger species contributed to reduced light penetration (i.e., greater shading), and examined the impact of shade on smaller species by testing whether their abundance and richness were lower in plots with less light penetration. Light penetration in plots ranged from 0.3% to 72.4%. Significant effects were more common when analyses focused on small plants that reached reproduction (i.e., flowering rooted units); focusing on only flowering plants (i.e., excluding nonflowering rooted units) can clarify community patterns. Plots with a greater mean species height had significantly lower light penetration, and plots with lower light penetration had significantly lower flowering abundance and richness of small species. However, the impact of shade on the flowering abundance and richness of small species was relatively small (R ² values between 8% and 15%) and depended on how we defined “small species.” Synthesis: Our results confirm that light penetration in herbaceous vegetation can be comparable to levels seen in forests, that plots with taller species cast more shade, and that flowering smaller species are less abundant and diverse in plots where light penetration is low. However, variation in mean plot height explained less than 10% of variation in light penetration, and light penetration explained between 5 and 15% of variation in the flowering abundance and richness of small species. Coupled with the fact that flowering small species were present even within the most heavily shaded plots, our results suggest that any advantage in light competition by large species is limited. One explanation is that at least some small species in these communities are shade‐tolerant. Shade tolerance in predominantly herbaceous communities, particularly among small plant species, requires further research.