SYNCHRONIZATION OF THE MARINE DINOFLAGELLATE AMPHIDINIUM CARTERI IN DENSE CULTURES1

Under improved conditions, Amphidinium carteri Hulburt can be obtained as dense cultures (5–9 × 10⁵ cells · ml^?1) 5 days after inoculation. The possible association of a marine bacterium with the alga is discussed. A method to synchronize this photosynthetic organism is described which is based on the endogenous rhythm of division and the effect of light-dark alternating periods.     

Plant sulfate assimilation genes: redundancy versus specialization

Sulfur is an essential nutrient present in the amino acids cysteine and methionine, co-enzymes and vitamins. Plants and many microorganisms are able to utilize inorganic sulfate and assimilate it into these compounds. Sulfate assimilation in plants has been extensively studied because of the many functions of sulfur in plant metabolism and stress defense. The pathway is highly regulated in a demand-driven manner. A characteristic feature of this pathway is that most of its components are encoded by small multigene families. This may not be surprising, as several steps of sulfate assimilation occur in multiple cellular compartments, but the composition of the gene families is more complex than simply organellar versus cytosolic forms. Recently, several of these gene families have been investigated in a systematic manner utilizing Arabidopsis reverse genetics tools. In this review, we will assess how far the individual isoforms of sulfate assimilation enzymes possess specific functions and what level of genetic redundancy is retained. We will also compare the genomic organization of sulfate assimilation in the model plant Arabidopsis thaliana with other plant species to find common and species-specific features of the pathway.     

Microbial N2O consumption in and above marine N2O production hotspots

The ocean is a net source of N₂O, a potent greenhouse gas and ozone-depleting agent. However, the removal of N₂O via microbial N₂O consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand N₂O consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time. We find that the substrate affinity, O₂ tolerance, and community composition of N₂O-consuming microbes in oxic waters differ from those in the underlying anoxic layers. Kinetic parameters determined here are used to model in situ N₂O production and consumption rates. Estimated in situ rates differ from measured rates, confirming the necessity to consider kinetics when predicting N₂O cycling. Microbes from the oxic layer consume N₂O under anoxic conditions at a much faster rate than microbes from anoxic zones. These experimental results are in keeping with model results which indicate that N₂O consumption likely takes place above the oxygen deficient zone (ODZ). Thus, the dynamic layer with steep O₂ and N₂O gradients right above the ODZ is a previously ignored potential gatekeeper of N₂O and should be accounted for in the marine N₂O budget.Subject terms: Water microbiology, Biogeochemistry, Microbial ecology     

Rethinking ecological inference: density dependence in reef fishes

We use a meta‐analysis of density dependence in reef fishes to evaluate how ecologists approach detection, inference, and estimation. We compared two groups of studies: those that detected effects of density on survival and those that did not. Distinctions between these groups have spawned heated debate about the processes that affect fish dynamics. Per capita effects of density were similar between the two groups, although total effects (and hence ambient density) were greater in studies that detected density effects. The majority of the variation in effects of density was not resolved by the classification of studies based on the authors' conclusions. These results suggest (1) that standard inferences based on null hypothesis tests may miss important sources of variation in effects and give rise to unnecessary debate; and (2) that estimation of effect sizes and model parameters (including their uncertainty) is a powerful alternative to detection of ecological processes.     

Nematosomes or nucleolus-like bodies in hypothalamic neurons,the subfornical organ and adenohypophysial cells of the rat

Summary Fibrillar intracytoplasmic bodies, generally referred to as nematosomes or nucleolar like bodies (NLBs), are not only observed in various types of neurons in the hypothalamus and subfornical organ but also in the glandular cells of the pars tuberalis and the pars intermedia hypophyses. According to their cytochemical properties the NLBs are probably of ribonucleoprotein nature. Within the neurons NLBs occur within perikarya and processes. Their presence within the neurosecretory nerve fibers of the neural lobe proves their ability to migrate within the axon. Morphologic modifications of NLBs are observed in stimulated neurons and after colchicine treatment. Colchicine causes a characteristic dense texture of NLBs and a peripheral agglomeration of mitochondria very similar to the rosette arrangement observed in oocytes. Our findings suggest a structural and functional similarity of NLBs in neurons and oocytes, in which their nucleolar origin appears obvious and where they seem to represent preribosomal material. It is very likely that the axonal migration of the NLBs reflects transport of ribosomal RNA for delayed utilization (as in oocytes).This paper is dedicated to Prof. F. Stutinsky for his 65th birthday.     

Identification of mouse langerin/CD207 in Langerhans cells and some dendritic cells of lymphoid tissues.

Human (h)Langerin/CD207 is a C-type lectin of Langerhans cells (LC) that induces the formation of Birbeck granules (BG). In this study, we have cloned a cDNA-encoding mouse (m)Langerin. The predicted protein is 66% homologous to hLangerin with conservation of its particular features. The organization of human and mouse Langerin genes are similar, consisting of six exons, three of which encode the carbohydrate recognition domain. The mLangerin gene maps to chromosome 6D, syntenic to the human gene on chromosome 2p13. mLangerin protein, detected by a mAb as a 48-kDa species, is abundant in epidermal LC in situ and is down-regulated upon culture. A subset of cells also expresses mLangerin in bone marrow cultures supplemented with TGF-beta. Notably, dendritic cells in thymic medulla are mLangerin-positive. By contrast, only scattered cells express mLangerin in lymph nodes and spleen. mLangerin mRNA is also detected in some nonlymphoid tissues (e.g., lung, liver, and heart). Similarly to hLangerin, a network of BG form upon transfection of mLangerin cDNA into fibroblasts. Interestingly, substitution of a conserved residue (Phe(244) to Leu) within the carbohydrate recognition domain transforms the BG in transfectant cells into structures resembling cored tubules, previously described in mouse LC. Our findings should facilitate further characterization of mouse LC, and provide insight into a plasticity of dendritic cell organelles which may have important functional consequences.     

Organ of Bellonci of an Antarctic crustacean,the marine isopod Glyptonotus antarcticus

The paired organ of Bellonci protrudes from the optic lobe of the giant Antarctic isopod, Glyptonotus antarcticus. It is linked to the cortex by a broad peduncle. No connection to the cuticle or “sensory pore organ” was found. A cluster of sensory-like cells forms two outer ciliary segments branching into numerous microvilli with microtubules. The putative sensory somata are irregular in shape and contain a very high density of glycogen granules. The two outer segments sprout from two pits of the soma in different directions, forming a right angle. Glial cells wrap around the sensory cells and also delimit lacunae into which bundles of microvilli project. These lacunae contain electron-dense granules of small size and with species-specific patterns. Lacunae and dense granules show features typical of a degeneration process in the sensory cells. This general morphology corresponds to the unilobular type of organ of Bellonci, known in other isopods; it differs from the plurilobular type with onion bodies found in other Crustacea.     

Food stealing in cockroaches

Relationships between food stealing and exploitation of main food sources were investigated in the German cockroach,Blattella germanica (L.) (Dictyoptera: Blattellidae). The occurrence of food stealing during food exploitation was associated with the course of depletion of the main food sources and not with spatial distribution or distance from shelter. Stolen pieces of food always appeared towards the end of exploitation of a food source. Their occurrence appeared to be a consequence of the exploitation of a food source rather than a specific strategy. The proportion of animals of different developmental stages observed with stolen pieces differed significantly from that in the general population. There were proportionally more males, females and large larvae and proportionally less small larvae with stolen pieces than on the main food source. These data suggest that stolen pieces appeared when competition for access to food increased, and that larger cockroaches (adults and larger larvae) were then dominant and benefited from monopolizing stolen pieces of food.     

Site-directed mutagenesis of penicillin-binding protein 3 of Escherichia coli: Role of Val-545

Abstract Val545 of the Escherichia coli penicillin-binding protein 3 is essential to the acyl transfer mechanism through which the active-site serine 307 is acylated by benzylpenicillin and cephalexin and to the mechanism through which the protein allows rapidly growing cells to divide.