Heating of a Local Region of a Branching Streamer as a Starting Point of a Space Leader and a Negative-Leader Step

Plasma Physics Reports - Localized plasma formations called space leaders are observed in streamer coronas of negative leaders of long laboratory sparks. The main leader completes a step when the...     

Geminiviruses: a tale of a plasmid becoming a virus

Background  

Geminiviruses (family Geminiviridae) are small single-stranded (ss) DNA viruses infecting plants. Their virion morphology is unique in the known viral world – two incomplete T = 1 icosahedra are joined together to form twinned particles. Geminiviruses utilize a rolling-circle mode to replicate their genomes. A limited sequence similarity between the three conserved motifs of the rolling-circle replication initiation proteins (RCR Reps) of geminiviruses and plasmids of Gram-positive bacteria allowed Koonin and Ilyina to propose that geminiviruses descend from bacterial replicons.     

Mechanisms of coexistence of a bacteria and a bacteriophage in a spatially homogeneous environment

When bacteriophage are added to laboratory bacteria populations, bacteria mutants that are resistant to the phage quickly dominate the population. The phage will only persist in the long‐term if there are sufficient bacteria in the population that show susceptibility to the phage. We investigated the mechanisms allowing for coexistence by adding the virulent bacteriophage φ6 to cultures of the bacterium Pseudomonas syringae pv. phaseolicola in a spatially homogeneous environment. We saw large differences between replicate cultures, in particular when one or both of the species persisted. These differences can be explained by variation in the timing of the appearance of various resistant phenotypes in the bacteria populations before the phage were added, which determines their relative frequencies within the populations. Although these resistant phenotypes have similar fitnesses in the presence and in the absence of the phage, they have a profound effect on the persistence of the phage. Our results give a clearer understanding of the ecological mechanisms that lead to the coexistence of bacteria and virulent phage in environments where there are no spatial refuges available to the bacteria population.     

Characterization of a protease of a feather-degrading Microbacterium species

AIMS: To characterize a new feather-degrading bacterium. METHODS AND RESULTS: The strain kr10 producing a high keratinolytic activity when cultured on native feather broth was identified as Microbacterium sp., based on phenotypical characteristics and 16S rDNA sequence. The bacterium presented optimum growth and feather-degrading activity at pH 7.0 and 30 degrees C. Complete feather degradation was achieved during cultivation. The keratinase was partially purified by gel filtration chromatography. It was optimally active at pH 7.0 and 55 degrees C. The enzyme was inhibited by 1,10-phenanthroline, EDTA, p-chloromercuribenzoic acid, 2-mercaptoethanol and metal ions like Hg(2+), Cu(2+) and Zn(2+). SIGNIFICANCE AND IMPACT OF THE STUDY: A new Microbacterium sp. strain was characterized presenting high feather-degrading activity, which appears to be associated to a metalloprotease-type keratinase. This micro-organism has enormous potential for use in biotechnological processes involving keratin hydrolysis.     

Effects of a disease affecting a predator on the dynamics of a predator-prey system

We study the effects of a disease affecting a predator on the dynamics of a predator-prey system. We couple an SIRS model applied to the predator population, to a Lotka-Volterra model. The SIRS model describes the spread of the disease in a predator population subdivided into susceptible, infected and removed individuals. The Lotka-Volterra model describes the predator-prey interactions. We consider two time scales, a fast one for the disease and a comparatively slow one for predator-prey interactions and for predator mortality. We use the classical “aggregation method” in order to obtain a reduced equivalent model. We show that there are two possible asymptotic behaviors: either the predator population dies out and the prey tends to its carrying capacity, or the predator and prey coexist. In this latter case, the predator population tends either to a “disease-free” or to a “disease-endemic” state. Moreover, the total predator density in the disease-endemic state is greater than the predator density in the “disease-free” equilibrium (DFE).     

Facile synthesis of a D-galactono-1,6-lactone derivative, a precursor of a copolyester

2,3,4,6-Tetra-O-methyl-d-galactonic acid (5) was readily prepared from d-galactono-1,4-lactone (1) in 47% yield. The sequence involves tritylation of HO-6 of 1, followed by O-permethylation and deprotection. Lactonization of 5 led to the per-O-methyl-d-galactono-1,6-lactone, which was copolymerized with epsilon-caprolactone by ring-opening polymerization catalyzed by scandium triflate. The incorporation of the sugar comonomer into the polyester chain was about 10%.     

Glycan expression as a tool for a deeper understanding of a reproductive gland in a skate of economic importance

Atlantoraja platana is an oviparous skate endemic to the south-west Atlantic Ocean, and is one of the skate species most exploited by local industrial bottom trawl fisheries. Oviparous elasmobranchs encapsulate their eggs in complex egg cases produced by the oviductal gland (OG). This organ is exclusively present in these fishes and comprises four distinct zones: club, baffle, papillary and terminal. The relative size and structural complexity of these zones correlate with mode of reproduction. Glycans are known to play major roles in reproduction so their distribution in each zone of the OG could explain the functional multiplicity of the gland in skates, but this topic has not been previously investigated. In this study, morphological, histochemical and lectin-histochemical analysis revealed various novel aspects of A. platana's OG. The club, papillary and terminal zones positively stained for periodic acid Schiff's reagent (PAS) and Alcian Blue (AB), indicating the presence of neutral and acid mucopolysaccharides. However, the buffle zone was negative for PAS and AB stains, but was positive for all the lectins used. Each zone of the OG had a characteristic pattern of glycan expression. Finally, we confirmed the presence of sperm but not sperm storage. This is the first lectin-histochemical study of the OG in chondrichtyan fish and it has proven to be an important tool to understand some of the mechanisms of fertility and reproductive success in economic important species such as A. platana.