Toward a dynamical understanding of microbial communities

The challenge of moving beyond descriptions of microbial community composition to the point where understanding underlying eco-evolutionary dynamics emerges is daunting. While it is tempting to simplify through use of model communities composed of a small number of types, there is a risk that such strategies fail to capture processes that might be specific and intrinsic to complexity of the community itself. Here, we describe approaches that embrace this complexity and show that, in combination with metagenomic strategies, dynamical insight is increasingly possible. Arising from these studies is mounting evidence of rapid eco-evolutionary change among lineages and a sense that processes, particularly those mediated by horizontal gene transfer, not only are integral to system function, but are central to long-term persistence. That such dynamic, systems-level insight is now possible, means that the study and manipulation of microbial communities can move to new levels of inquiry. This article is part of the theme issue ‘Conceptual challenges in microbial community ecology’

A submillimetre wavelength spectral line search of the Orion molecular cloud core

A submillimetre wavelength molecular line search of the Orion molecular cloud has been made covering a total of about 5 percent of the frequency range 342.8 - 358.6 GHz. This search, coupled with the authors' previous observations of submillimetre transitions in this cloud, has led to the detection of 22 transitions of 14 molecular species, of which 16 are reported here for the first time. No unidentified lines have been detected in the present search. Mapping observations have been obtained for several of the lines and, in the case of H2CO the authors have been able to compare the present data with that obtained from other telescopes, to estimate the density and abundance in the emitting region

ECONOMIC IMPACT EVALUATION OF GLOBAL MARKETING SUPPORT SERVICES - AN EXPORTS ASSISTANCE PROGRAM ON THE ECONOMY OF ARKANSAS

This study determines the impact of Global Marketing Support Services (GMSS) - an exports assistance program in assisting 13 small and medium sized businesses to export. The total impact of exports (direct, indirect and induced effects) on added value, employment, labor income and tax impacts in Arkansas are estimated using Impact Analysis for Planning (IMPLAN).International Relations/Trade,

Controlling thermal chaos in the mantle by positive feedback from radiative thermal conductivity

International audienceThe thermal conductivity of mantle materials has two components, the lattice component klat from phonons and the radiative component krad due to photons. These two contributions of variable thermal conductivity have a nonlinear dependence in the temperature, thus endowing the temperature equation in mantle convection with a strongly nonlinear character. The temperature derivatives of these two mechanisms have different signs, with ?klat /?T negative and dkrad /dT positive. This offers the possibility for the radiative conductivity to control the chaotic boundary layer instabilities developed in the deep mantle. We have parameterized the weight factor between krad and klat with a dimensionless parameter f , where f = 1 corresponds to the reference conductivity model. We have carried out two-dimensional, time-dependent calculations for variable thermal conductivity but constant viscosity in an aspect-ratio 6 box for surface Rayleigh numbers between 106 and 5 × 106. The averaged Péclet numbers of these flows lie between 200 and 2000. Along the boundary in f separating the chaotic and steady-state solutions, the number decreases and the Nusselt number increases with internal heating, illustrating the feedback between internal heating and radiative thermal conductivity. For purely basal heating situation, the time-dependent chaotic flows become stabilized for values of f of between 1.5 and 2. The bottom thermal boundary layer thickens and the surface heat flow increases with larger amounts of radiative conductivity. For magnitudes of internal heating characteristic of a chondritic mantle, much larger values of f , exceeding 10, are required to quench the bottom boundary layer instabilities. By isolating the individual conductive mechanisms, we have ascertained that the lattice conductivity is partly responsible for inducing boundary layer instabilities, while the radiative conductivity and purely depth-dependent conductivity exert a stabilizing influence and help to control thermal chaos developed in the deep mantle. These results have been verified to exist also in three-dimensional geometry and would argue for the need to consider the potentially important role played by radiative thermal conductivity in controlling chaotic flows in time-dependent mantle convection, the mantle heat transfer, the number of hotspots and the attendant mixing of geochemical anomalies

Characterization of the monocyte-specific esterase (MSE) gene

Carboxylic esterases are widely distributed in hematopoietic cells. Monocytes express the esterase isoenzyme (termed 'monocyte-specific esterase', MSE) that can be inhibited by NaF in the alpha-naphthyl acetate cytochemical staining. We examined the expression of MSE in normal cells and primary and cultured leukemia-lymphoma cells. The MSE protein was demonstrated by isoelectric focusing (IEF); MSE mRNA expression was investigated by Northern blotting and reverse transcriptase-polymerase chain reaction (RT-PCR). The following samples were positive for MSE protein and Northern mRNA expression: 20/24 monocytic, 4/32 myeloid, and 1/20 erythroid-megakaryocytic leukemia cell lines, but none of the 112 lymphoid leukemia or lymphoma cell lines; of the normal purified cell populations only the monocytes were positive whereas, T, B cells, and granulocytes were negative; of primary acute (myelo) monocytic leukemia cells (CD14-positive, FAB M4/M5 morphology) 14/20 were Northern mRNA and 11/14 IEF protein positive. RT-PCR revealed MSE expression in 29/49 Northern-negative lymphoid leukemia-lymphoma cell lines. The RT-PCR signals in monocytic cell lines were on average 50-fold stronger than the mostly weak trace expression in lymphoid specimens. On treatment with various biomodulators, only all-trans retinoic acid significantly upregulated MSE message and protein levels but could not induce new MSE expression in several leukemia cell lines; lipopolysaccharide and interferon-gamma increased MSE expression in normal monocytes. Analysis of DNA methylation with sensitive restriction enzymes showed no apparent regulation of gene expression by differential methylation; the MSE gene is evolutionarily conserved among mammalian species; the half-life of the human MSE transcripts was about 5-6 h. The extent of MSE expression varied greatly among different monocytic leukemia samples. However, the MSE overexpression in a significant number of specimens was not associated with gene amplification, gross structural rearrangements or point mutations within the cDNA region. Taken together, the results suggest that MSE expression is not absolutely specific for, but strongly associated with cells of the monocytic lineage; MSE is either not expressed at all or expressed at much lower levels in cells from other lineages. The biological significance, if any, of rare MSE messages in lymphoid cells detectable only by the hypersensitive RT-PCR remains unclear. Further studies on the regulation of this gene and on the physiological function of the enzyme will no doubt be informative with respect to its striking overexpression in some malignant cells and to a possible role in the pathobiology of monocytic leukemias