A Temporally Explicit Production Efficiency Model for Fuel Load Allocation in Southern Africa

Abstract We present a regional fuel load model (1 km² spatial resolution) applied in the southern African savanna region. The model is based on a patch-scale production efficiency model (PEM) scaled up to the regional level using empirical relationships between patch-scale behavior and multi-source remote sensing data (spatio-temporal variability of vegetation and climatic variables). The model requires the spatial distribution of woody vegetation cover, which is used to determine separate respiration rates for tree and grass. Net primary production, grass and tree leaf death, and herbivory are also taken into account in this mechanistic modeling approach. The fuel load model has been calibrated and validated from independent measurements taken from savanna vegetation in Africa southward from the equator. A sensitivity analysis on the effect of climate variables (incoming radiation, air temperature, and precipitation) has been conducted to demonstrate the strong role that water availability has in determining productivity and subsequent fuel load over the southern African region. The model performance has been tested in four different areas representative of a regional increasing rainfall gradient—Etosha National Park, Namibia, Mongu and Kasama, Zambia, as well as in Kruger National Park, South Africa. Within each area, we analyze model output from three different magnitudes of canopy coverage (<5, 30, and 50%). We find that fuel load ranges predicted by the model are globally in agreement with field measurements for the same year. High rainfall sustains green herbaceous production late in the dry season and delays tree leaf litter production. Effect of water on production varies across the rainfall gradient with delayed start of green material production in more arid regions.     

Selective inactivation of MAO-B by benzyl-dimethyl-silyl-methanamines in vitro

The alpha-silyl amines benzyl-dimethyl-silyl-methanamine and the p-fluoro and p-chloro derivatives are potent time-dependent inhibitors of rat brain MAO-B. The inhibition exhibits saturation kinetics, takes place in the enzyme active-site and is irreversible. The most potent inhibitor in the series is 4-fluorobenzyl-dimethyl-silyl-methanamine (KI = 11 microM, tau 1/2 = 2.3 min). Its selectivity for the B-form relative to the A-form of rat brain MAO is higher than 10(4). Benzyl-dimethyl-silyl-methanamines may represent a new family of anti-Parkinsonian agents.     

Immobilization of microorganisms by adhesion: interplay of electrostatic and nonelectrostatic interactions

The adhesion of three microorganisms (Saccharomyces cerevisiae, Acetobacter aceti, and Moniliella pollinis) to different materials has been studied using various supports (glass, metals, plastics), some of which were treated by an Fe(III) solution. The surface properties of the cells were characterized by the zeta potential and an index of hydrophobicity; characterization of the supports involved surface chemical analysis (XPS) and contact angle measurements. Cell suspensions in pure water at a given pH were left to settle on plates; the latter were then rinsed and examined microscopically, Saccharomyces cerevisiae and A. aceti adhere to metals under certain pH conditions but do not adhere to any of the other materials tested unless it is previously treated by ferric ions; adhesion of these hydrophilic cells is essentially controlled by electrostatic interactions. Moniliella pollinis adhere spontaneously to glass and to polymeric materials, but its attachment is also influenced by cell-cell or cell-support electrostatic repulsions; near the cell isoelectric point, cell flocculation is competing with adhesion to a support.     

Negative dominance in gene lamB: random assembly of secreted subunits issued from different polysomes

lamB is the structural gene for the lambda receptor, an oligomeric outer membrane protein from Escherichia coli K12 involved in phage lambda adsorption. We show that, under certain conditions, in a strain diploid for gene lamB, all the missense lamB mutations conferring lambda resistance that we have tested are dominant with respect to wild-type. We propose a model which allows a quantitative interpretation of the data. It is based on negative complementation at the level of oligomerisation. Wild-type and mutant subunits would assemble at random forming homo- and hetero-oligomers. Only wild-type homo-oligomers would be efficient for phage inactivation. For some classes of missense mutations the hetero-oligomers would have the capacity to bind, but not to inactivate the phage. The model confirms that active lambda receptor is a trimer and implies that for this secreted protein there is no preferential assembly of subunits originating from the same polysome.     

First chromosome scale genomes of ithomiine butterflies (Nymphalidae: Ithomiini): Comparative models for mimicry genetic studies

The ithomiine butterflies (Nymphalidae: Danainae) represent the largest known radiation of Müllerian mimetic butterflies. They dominate by number the mimetic butterfly communities, which include species such as the iconic neotropical Heliconius genus. Recent studies on the ecology and genetics of speciation in Ithomiini have suggested that sexual pheromones, colour pattern and perhaps hostplant could drive reproductive isolation. However, no reference genome was available for Ithomiini, which has hindered further exploration on the genetic architecture of these candidate traits, and more generally on the genomic patterns of divergence. Here, we generated high-quality, chromosome-scale genome assemblies for two Melinaea species, M. marsaeus and M. menophilus, and a draft genome of the species Ithomia salapia. We obtained genomes with a size ranging from 396 to 503 Mb across the three species and scaffold N50 of 40.5 and 23.2 Mb for the two chromosome-scale assemblies. Using collinearity analyses we identified massive rearrangements between the two closely related Melinaea species. An annotation of transposable elements and gene content was performed, as well as a specialist annotation to target chemosensory genes, which is crucial for host plant detection and mate recognition in mimetic species. A comparative genomic approach revealed independent gene expansions in ithomiines and particularly in gustatory receptor genes. These first three genomes of ithomiine mimetic butterflies constitute a valuable addition and a welcome comparison to existing biological models such as Heliconius, and will enable further understanding of the mechanisms of adaptation in butterflies.     

In vitro colonization ability of human colon mucosa by exogenous Lactobacillus strains

Abstract A 5.4 kb Hind III DNA fragment carrying the gene encoding raw starch-digesting α-amylase (RSDA), has been previously cloned from Bacillus circulans F-2 and expressed in Escherichia coli [Kim et al. (1990) Biochim. Biophys. Acta 1048, 2233–2238]. Interestingly, when the cell extract of E. coli harboring a plasmid carrying this fragment was incubated with l M NaCl, it exhibited about 10 times higher enzyme activity than when assayed without NaCl. Differential zymograms showed two different amylase activities: one for RSDA and the other for a salt-dependent a-amylase (SDA). Even though RSDA activity was detected without NaCl, SDA activity was detected only in high concentrations of NaCl. SDA activity was fully detected at above l M NaCl. Results from subcloning of the genes, fractionation analysis of cell extracts, and immunological assays clearly suggested that the two amylases are genetically distinct and that genes for both enzymes are closely linked on the 5.4 kb DNA fragment.     

The endometrium of the immature rabbit stimulated by an estrogen and treated with a progestogen. Scanning electron microscopy study

The endometrium of rabbits, treated by the usual pharmacology methods designed for the measurement of the pseudogestagen effect, was studied by scanning electron microscopy. Estrogen stimulation was followed by a multiplication of the number of ciliated cells. Treatment with progesterone lead to a decrease in the numbers of microvilli and to the appearance of rounded bulges which increased in numbers as the progesterone dose level increased. These changes were quite close to those observed in post menopausal women under estro-progestogen treatment.     

Neisseria gonorrhoeae prepilin export studied in Escherichia coli.

The pilE gene of Neisseria gonorrhoeae MS11 and a series of pilE-phoA gene fusions were expressed in Escherichia coli. The PhoA hybrid proteins were shown to be located in the membrane fraction of the cells, and the prepilin product of the pilE gene was shown to be located exclusively in the cytoplasmic membrane. Analysis of the prepilin-PhoA hybrids showed that the first 20 residues of prepilin can function as an efficient export (signal) sequence. This segment of prepilin includes an unbroken sequence of 8 hydrophobic or neutral residues that form the N-terminal half of a 16-residue hydrophobic region of prepilin. Neither prepilin nor the prepilin-PhoA hybrids were processed by E. coli leader peptidase despite the presence of two consensus cleavage sites for this enzyme just after this hydrophobic region. Comparisons of the specific molecular activities of the four prepilin-PhoA hybrids and analysis of their susceptibility to proteolysis by trypsin and proteinase K in spheroplasts allow us to propose two models for the topology of prepilin in the E. coli cytoplasmic membrane. The bulk of the evidence supports the simplest of the two models, in which prepilin is anchored in the membrane solely by the N-terminal hydrophobic domain, with the extreme N terminus facing the cytoplasm and the longer C terminus facing the periplasm.     

Repeated DNA sequences in the microbat species Miniopterus schreibersi (Vespertilionidae; Chiroptera)

Repetitive DNA sequences represent a substantial component of eukaryotic genomes. These sequences have been described and characterized in many mammalian species. However, little information about repetitive DNA sequences is available in bat species. Here we describe an EcoRI family of repetitive DNA sequences present in the species Miniopterus schreibersi. These repetitive sequences are 57.85%, A-T rich, organized in tandem, and with a monomer unit length of 904 bp. Methylation analysis using the isoesquizomer pair MspI and HpaII indicates that the cytosines present in the sequences CCGG are partially methylated. Furthermore, Southern blot analysis demonstrated that these DNA sequences are absent in the genomes of four related microbat species and suggest that it could be specific to the M. schreibersi genome.     

Manipulation of <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid biosynthesis pathways in <Emphasis Type="Italic">Solanum lycopersicum</Emphasis>: elevated GDP-mannose pyrophosphorylase activity enhances <Emphasis Type="SmallCaps">l</Emphasis>-ascorbate levels in red fruit

Ascorbate (AsA) plays a fundamental role in redox homeostasis in plants and animals, primarily by scavenging reactive oxygen species. Three genes, representing diverse steps putatively involved in plant AsA biosynthesis pathways, were cloned and independently expressed in Solanum lycopersicum (tomato) under the control of the CaMV 35S promoter. Yeast-derived GDP-mannose pyrophosphorylase (GMPase) and arabinono-1,4-lactone oxidase (ALO), as well as myo-inositol oxygenase 2 (MIOX2) from Arabidopsis thaliana, were targeted. Increases in GMPase activity were concomitant with increased AsA levels of up to 70% in leaves, 50% in green fruit, and 35% in red fruit. Expression of ALO significantly pulled biosynthetic flux towards AsA in leaves and green fruit by up to 54 and 25%, respectively. Changes in AsA content in plants transcribing the MIOX2 gene were inconsistent in different tissue. On the other hand, MIOX activity was strongly correlated with cell wall uronic acid levels, suggesting that MIOX may be a useful tool for the manipulation of cell wall composition. In conclusion, the Smirnoff–Wheeler pathway showed great promise as a target for biotechnological manipulation of ascorbate levels in tomato.