Cyanobacterial mats: Microanalysis of community metabolism

The microbial communities in two sites were studied using several approaches: (1) light microscopy; (2) the measurement of microprofiles of oxygen and sulfide at the surface of the microbial mat; (3) the study of diurnal variation of oxygen and sulfides; (4) in situ measurement of photosynthesis and sulfate reduction and study of the coupling of these two processes; (5) measurement of glutathione in the upper layers of the microbial mat as a possible oxygen quencher; (6) measurement of reduced iron as a possible intermediate electron donor along the established redoxcline in the mats; (7) measurement of dissolved phosphate as an indicator of processes of break down of organic matter in these systems; and (8) measurement of carbon dioxide in the interstitial water and its delta C-13 in an attempt to understand the flow of CO2 through the systems. Microbial processes of primary production and initial degradation at the most active zone of the microbial mat were analyzed

Comparison of two-dimensional and three-dimensional computational fluid dynamics solutions for a vectoring turbine engine exhaust nozzle

Computational fluid dynamics (CFD) solutions for vectored nozzle flow fields can be used to predict nozzle performance, design ground test facility hardware, and size nozzle instrumentation. The purpose of this research was to compare two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics (CFD) solutions for a twodimensional vectoring exhaust nozzle of rectangular cross section. The motivation for using 2D CFD codes as opposed to 3D CFD codes is that 2D (planar or axisymmetric) CFD simulation results generally have less truncation and round off error, they require less labor and fewer computational resources, they are less subject to interpretive errors; and consequently, results can be provided in a more responsive and timely manner. The parameters that were compared were mass flow, axial gross thrust, and vertical gross thrust. The simulations have been performed at three nozzle pressure ratios, with uniform nozzle inlet boundary conditions. These inlet boundary conditions are based on one-dimensional turbine engine math model predictions. The assumption of uniform nozzle entrance boundary conditions is expected to negate some of the potential for three-dimensional effects; therefore this investigation represents a best case comparison. The CFD codes (PARC2D and PARC3D) used to model the 2D/CD (two-dimensional convergent-divergent) nozzle flow fields are based on the finite difference form of the Reynolds-averaged Navier-Stokes equations. Usage of the PARC codes is restricted to fluids which have thermally and calorically perfect equations of state and a constant Prandtl number. The codes used to solve these equations incorporated a variant of the implicit approximate factorization algorithm of Beam and Warming. The codes also incorporated a modified Baldwin and Lomax turbulence model. For the sake of conserving resources, and with the aim of improving simulation responsiveness, ways to obviate a full 3D treatment of 2D/CD nozzle performance predictions were investigated. These methods included; 1) Comparisons of 2D and 3D solutions at three nozzle pressure ratios (NPR) for a vectored nozzle configuration of constant area ratio and vector angle. 2) An aspect ratio (nozzle width/nozzle height at the nozzle entrance) parametric study to investigate the limits of the more economical 2D CFD performance simulation results

Iron-stimulated N2 fixation and growth in natural and cultured populations of the planktonic marine cyanobacteria Trichodesmium spp.

In light of recent proposals that iron (Fe) availability may play an important role in controlling oceanic primary production and nutrient flux, its regulatory impact on N2 fixation and production dynamics was investigated in the widespread and biogeochemically important diazotrophic, planktonic cyanobacteria Trichodesmium spp. Fe additions, as FeCl3 and EDTA- chelated FeCl3, enhanced N2 fixation (nitrogenase activity), photosynthesis (CO2 fixation), and growth (chlorophyll a production) in both naturally occurring and cultured (on unenriched oligotrophic seawater) Trichodesmium populations. Maximum enhancement of these processes occurred under FeEDTA- amended conditions. On occasions, EDTA alone led to enhancement. No evidence for previously proposed molybdenum or phosphorus limitation was found. Our findings geographically extend support for Fe limitation of N2 fixation and primary production to tropical and subtropical oligotrophic ocean waters often characterized by Trichodesmium blooms

A denitrifying community associated with a major, marine nitrogen fixer

The diazotrophic cyanobacterium, Trichodesmium, is an integral component of the marine nitrogen cycle and contributes significant amounts of new nitrogen to oligotrophic, tropical/subtropical ocean surface waters. Trichodesmium forms macroscopic, fusiform (tufts), spherical (puffs) and raft-like colonies that provide a pseudobenthic habitat for a host of other organisms including marine invertebrates, microeukaryotes and numerous other microbes. The diversity and activity of denitrifying bacteria found in association with the colonies was interrogated using a series of molecular-based methodologies targeting the gene encoding the terminal step in the denitrification pathway, nitrous oxide reductase (nosZ). Trichodesmium spp. sampled from geographically isolated ocean provinces (the Atlantic Ocean, the Red Sea and the Indian Ocean) were shown to harbor highly similar, taxonomically related communities of denitrifiers whose members are affiliated with the Roseobacter clade within the Rhodobacteraceae (Alphaproteobacteria). These organisms were actively expressing nosZ in samples taken from the mid-Atlantic Ocean and Red Sea implying that Trichodesmium colonies are potential sites of nitrous oxide consumption and perhaps earlier steps in the denitrification pathway also. It is proposed that coupled nitrification of newly fixed N is the most likely source of nitrogen oxides supporting nitrous oxide cycling within Trichodesmium colonies

Farnesylated Nuclear Proteins Kugelkern and Lamin Dm0 Affect Nuclear Morphology by Directly Interacting with the Nuclear Membrane

Nuclear shape changes are observed during a variety of developmental processes, pathological conditions and ageing. Here, the molecular mechanism is analyzed how the farnesylated nuclear proteins interact with the nuclear envelope and deform the phospholipid bilayer

Meiosis in Mice without a Synaptonemal Complex

The synaptonemal complex (SC) promotes fusion of the homologous chromosomes (synapsis) and crossover recombination events during meiosis. The SC displays an extensive structural conservation between species; however, a few organisms lack SC and execute meiotic process in a SC-independent manner. To clarify the SC function in mammals, we have generated a mutant mouse strain (Sycp1−/−Sycp3−/−, here called SC-null) in which all known SC proteins have been displaced from meiotic chromosomes. While transmission electron microscopy failed to identify any remnants of the SC in SC-null spermatocytes, neither formation of the cohesion axes nor attachment of the chromosomes to the nuclear membrane was perturbed. Furthermore, the meiotic chromosomes in SC-null meiocytes achieved pre-synaptic pairing, underwent early homologous recombination events and sustained a residual crossover formation. In contrast, in SC-null meiocytes synapsis and MLH1-MLH3-dependent crossovers maturation were abolished, whereas the structural integrity of chromosomes was drastically impaired. The variable consequences that SC inactivation has on the meiotic process in different organisms, together with the absence of SC in some unrelated species, imply that the SC could have originated independently in different taxonomic groups

Abundances of Iron-Binding Photosynthetic and Nitrogen-Fixing Proteins of Trichodesmium Both in Culture and In Situ from the North Atlantic

Marine cyanobacteria of the genus Trichodesmium occur throughout the oligotrophic tropical and subtropical oceans, where they can dominate the diazotrophic community in regions with high inputs of the trace metal iron (Fe). Iron is necessary for the functionality of enzymes involved in the processes of both photosynthesis and nitrogen fixation. We combined laboratory and field-based quantifications of the absolute concentrations of key enzymes involved in both photosynthesis and nitrogen fixation to determine how Trichodesmium allocates resources to these processes. We determined that protein level responses of Trichodesmium to iron-starvation involve down-regulation of the nitrogen fixation apparatus. In contrast, the photosynthetic apparatus is largely maintained, although re-arrangements do occur, including accumulation of the iron-stress-induced chlorophyll-binding protein IsiA. Data from natural populations of Trichodesmium spp. collected in the North Atlantic demonstrated a protein profile similar to iron-starved Trichodesmium in culture, suggestive of acclimation towards a minimal iron requirement even within an oceanic region receiving a high iron-flux. Estimates of cellular metabolic iron requirements are consistent with the availability of this trace metal playing a major role in restricting the biomass and activity of Trichodesmium throughout much of the subtropical ocean