Bradyrhizobium japonicum mutants defective in root-nodule bacteroid development and nitrogen fixation

The genome of the slow-growing Bradyrhizobium japonicum (strain 110) was mutagenized with transposon Tn5. A total of 1623 kanamycin/streptomycin resistant derivatives were screened in soybean infection tests for nodulation (Nod) and symbiotic nitrogen fixation (Fix). In this report we describe 14 strains possessing a stable, reproducible Nod⁺Fix^- phenotype. These strains were also grown under microaerobic culture conditions to test them for free-living nitrogen fixation activity (Nif). In addition to strains having reduced Fix and Nif activities, there were also strains that had reduced symbiotic Fix activity but were Nif⁺ ex planta.Analysis of the genomic structure revealed that the majority of the strains had a single Tn5 insertion without any further apparent physical alteration. A few strains had additional insertions (by Tn5 or IS50), or a deletion, or had cointegrated part of the vector used for Tn5 mutagenesis. One of the insertions was found in a known nif gene (nifD) whereas all other mutations seem to affect different, hitherto unknown genes or operons.Several mutant strains had an altered nodulation phenotype, inducing numerous, small, widely distributed nodules. Light and electron microscopy revealed that most of these mutants were defective in different stages of bacteroid development and/or bacteroid persistence. The protein patterns of the mutants were inspected by two-dimensional gel electrophoresis after labelling microaerobic cultures with l-(³⁵S)methionine. Of particular interest were mutants lacking a group of proteins the synthesis of which was known to be under oxygen control. Such strains can be regarded as potential regulatory mutants.     

Desulfoferrodoxin of Clostridium acetobutylicum functions as a superoxide reductase

Desulfoferrodoxin (cac2450) of Clostridium acetobutylicum was purified after overexpression in E. coli. In an in vitro assay the enzyme exhibited superoxide reductase activity with rubredoxin (cac2778) of C. acetobutylicum as the proximal electron donor. Rubredoxin was reduced by ferredoxin:NADP(+) reductase from spinach and NADPH. The superoxide anions, generated from dissolved oxygen using Xanthine and Xanthine oxidase, were reduced to hydrogen peroxide. Thus, we assume that desulfoferrodoxin is the key factor in the superoxide reductase dependent part of an alternative pathway for detoxification of reactive oxygen species in this obligate anaerobic bacterium.     

Inhibitors of actin polymerisation stimulate arachidonic acid release and 5-lipoxygenase activation by upregulation of Ca2+ mobilisation in polymorphonuclear leukocytes involving Src family kinases

Here, we show that actin polymerisation inhibitors such as latrunculin B (LB), and to a minor extent also cytochalasin D (Cyt D), enhance the release of arachidonic acid (AA) as well as nuclear translocation of 5-lipoxygenase (5-LO) and 5-LO product synthesis in human polymorphonuclear leukocytes (PMNL), challenged with thapsigargin (TG) or N-formyl-methionyl-leucyl-phenylalanine. The concentration-dependent effects of LB (EC50 approximately 200 nM) declined with prolonged preincubation (>3 min) prior TG and were barely detectable when PMNL were stimulated with Ca2+-ionophores. Investigation of the stimulatory mechanisms revealed that LB (or Cyt D) elicits Ca2+ mobilisation and potentiates stimulus-induced elevation of intracellular Ca2+, regardless of the nature of the stimulus. LB caused rapid but only moderate activation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK)2. The selective Src family kinase inhibitors PP2 and SU6656 blocked LB- or Cyt D-mediated Ca2+ mobilisation and suppressed the upregulatory effects on AA release and 5-LO product synthesis, without affecting AA metabolism evoked by ionophore alone. We conclude that in PMNL, inhibitors of actin polymerisation cause enhancement of intracellular Ca2+ levels through Src family kinase signaling, thereby facilitating stimulus-induced release of AA and 5-LO product formation.     

Seroprevalence and risk factors for Helicobacter pylori infection in Greenlanders

BACKGROUND: In contrast to most populations worldwide, the incidence of gastric cancer increases among Inuit in Greenland. Contributing factors to this increase are unknown, but Helicobacter pylori may be involved. However, little is known regarding the epidemiology of H. pylori in Arctic communities. With the aim of determining age-specific prevalence, risk factors, and association with clinical conditions of H. pylori infection, we carried out a population-based study of H. pylori in Sisimiut, the second biggest town of Greenland. MATERIALS AND METHODS: A population-based sample of 685 persons had serum drawn that was analyzed for H. pylori IgG antibodies using enzyme-linked immunosorbent assay (ELISA). Risk factors analyses were carried out using multivariate logistic regression models. RESULTS: The seroprevalence was lowest among children aged 0-4 years (6%), but increased rapidly thereafter. In persons aged 15-87 years the seroprevalence had stabilized around 58%. Total number of children in household, number of older, but not younger, siblings and narrow age gap to closest older sibling were associated with H. pylori seropositivity. In contrast, number of adults in household and socioeconomic status did not influence serostatus. CONCLUSIONS: The age-specific prevalence pattern in Greenland is intermediate between that of developing and developed countries. The risk factor pattern indicates crowding and older siblings in particular to be key elements in risk of infection.     

Average protein density is a molecular-weight-dependent function

The mass density of proteins is a relevant basic biophysical quantity. It is also a useful input parameter, for example, for three-dimensional structure determination by protein crystallography and studies of protein oligomers in solution by analytic ultracentrifugation. We have performed a critical analysis of published, theoretical, and experimental investigations about this issue and concluded that the average density of proteins is not a constant as often assumed. For proteins with a molecular weight below 20 kDa, the average density exhibits a positive deviation that increases for decreasing molecular weight. A simple molecular-weight-depending function is proposed that provides a more accurate estimate of the average protein density.     

Intestinal proteases of free-living and parasitic astigmatid mites

Among arthropod pests, mites are responsible for considerable damage to crops, humans and other animals. However, detailed physiological data on these organisms remain sparse, mainly because of their small size but possibly also because of their extreme diversity. Focusing on intestinal proteases, we draw together information from three distinct mite species that all feed on skin but have separately adapted to a free-living, a strictly ecto-parasitic and a parasitic lifestyle. A wide range of studies involving immunohistology, molecular biology, X-ray crystallography and enzyme biochemistry of mite gut proteases suggests that these creatures have diverged considerably as house dust mites, sheep scab mites and scabies mites. Each species has evolved a particular variation of a presumably ancestral repertoire of digestive enzymes that have become specifically adapted to their individual environmental requirements.     

Climate change, conservation and management: an assessment of the peer-reviewed scientific journal literature

Recent reviews of the conservation literature indicate that significant biases exist in the published literature regarding the regions, ecosystems and species that have been examined by researchers. Despite the global threat of climatic change, similar biases may be occurring within the sub-discipline of climate-change ecology. Here we hope to foster critical thought and discussion by considering the directions taken by conservation researchers when addressing climate change. To form a quantitative basis for our perspective, we assessed 248 papers from the climate change literature that considered the conservation management of biodiversity and ecosystems. We found that roughly half of the studies considered climate change in isolation from other threatening processes. We also found that the majority of surveyed scientific publications were conducted in the temperate forests of Europe and North America. Regions such as Latin America that are rich in biodiversity but may have low adaptive capacity to climate change were not well represented. We caution that such biases in research effort may be distracting our attention away from vulnerable regions, ecosystems and species. Specifically we suggest that the under-representation of research from regions low in adaptive capacity and rich in biodiversity requires international collaboration by those experienced in climate-change research, with researchers from less wealthy nations who are familiar with local issues, ecosystems and species. Furthermore, we caution that the propensity of ecologists to work in essentially unmodified ecosystems may fundamentally hamper our ability to make useful recommendations in a world that is experiencing significant global change.     

Cytosolic aminoacyl-tRNA synthetases: Unanticipated relocations for unexpected functions

Prokaryotic and eukaryotic cytosolic aminoacyl-tRNA synthetases (aaRSs) are essentially known for their conventional function of generating the full set of aminoacyl-tRNA species that are needed to incorporate each organism's repertoire of genetically-encoded amino acids during ribosomal translation of messenger RNAs. However, bacterial and eukaryotic cytosolic aaRSs have been shown to exhibit other essential nonconventional functions. Here we review all the subcellular compartments that prokaryotic and eukaryotic cytosolic aaRSs can reach to exert either a conventional or nontranslational role. We describe the physiological and stress conditions, the mechanisms and the signaling pathways that trigger their relocation and the new functions associated with these relocating cytosolic aaRS. Finally, given that these relocating pools of cytosolic aaRSs participate to a wide range of cellular pathways beyond translation, but equally important for cellular homeostasis, we mention some of the pathologies and diseases associated with the dis-regulation or malfunctioning of these nontranslational functions.     

Drosophila Tel2 Is Expressed as a Translational Fusion with EpsinR and Is a Regulator of Wingless Signaling

Tel2, a protein conserved from yeast to vertebrates, is an essential regulator of diverse cellular processes including telomere maintenance, DNA damage checkpoints, DNA repair, biological clocks, and cell signaling. The Drosophila Tel2 protein is produced as a translational fusion with EpsinR, a Clathrin adapter that facilitates vesicle trafficking between the Golgi and endosomes. EpsinR and Tel2 are encoded by a Drosophila gene called lqfR. lqfR is required for viability, and its specific roles include cell growth, proliferation, and planar cell polarity. We find that all of these functions of lqfR are attributed entirely to Tel2, not EpsinR. In addition, we find that Drosophila LqfR/Tel2 is a component of one or more protein complexes that contain E-cadherin and Armadillo. Moreover, Tel2 modulates E-cadherin and Armadillo cellular dynamics. We propose that at least one of the functions of Drosophila Tel2 is regulation of Wingless signaling.     

Brugia malayi: whole genome amplification for genomic characterization of filarial parasites

Genetic characterization of field isolates and clinical specimens of filarial nematodes is often limited by a shortage of DNA; therefore, we evaluated a multiple displacement amplification (MDA) based whole genome amplification method. The quality of amplified DNA was examined by conventional PCR, real-time PCR, and DNA hybridization. MDA of 5.0 ng of adult Brugia malayi DNA and one-fifteenth of the DNA isolated from a single microfilaria resulted in 6.3 and 4.2 μg of amplified DNA, respectively. Amplified DNA was equivalent to native genomic DNA for hybridization to B. malayi BAC library clones or to an oligonucleotide microarray with approximately 18,000 filarial DNA sequences. MDA is useful for whole genome amplification of filarial DNA from very small amounts of starting material. This technology will permit detailed studies of genetic diversity that were not previously feasible.