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Mosaic Structure (mosaic + structure)
Selected AbstractsAnalysis of the Pseudomonas aeruginosa oprD gene from clinical and environmental isolatesENVIRONMENTAL MICROBIOLOGY, Issue 12 2002Jean-Paul Pirnay Summary Genomes are constantly evolving. Our report highlights the wide mutational diversity of clinical as well as environmental isolates, compared with the laboratory strain(s), through the systematic genetic analysis of a chromosomal porin gene (oprD) in relation to a specific antibiotic resistance. Mutational inactivation of the oprD gene is associated with carbapenem resistance in Pseudomonas aeruginosa. The sequence of the oprD gene of 55 Pseudomonas aeruginosa natural isolates obtained from across the world , from sources as diverse as patients and rhizospheres , was analysed. A microscale mosaic structure for this gene , resulting from multiple intra- and possibly interspecies recombinational events , is reported. An array of independent and seemingly fast-occurring defective oprD mutations were found, none of which had been described before. A burn wound isolate demonstrated unusually high overall sequence variability typical of mutator strains. We also present evidence for the existence of OprD homologues in other fluorescent pseudomonads. [source] ENVIRONMENT-DEPENDENT ADMIXTURE DYNAMICS IN A TIGER SALAMANDER HYBRID ZONEEVOLUTION, Issue 6 2004Benjamin M. Fitzpatrick Abstract After an estimated five million years of independent evolution, the barred tiger salamander (Ambystoma tigrinum mavortium) was introduced by bait dealers into the native range of the California tiger salamander (A. californiense). Hybridization and backcrossing have been occurring in central California for 50,xs60 years, or an estimated 15,30 generations. We studied genetic and ecological factors influencing admixture of these two divergent gene pools by analyzing frequencies of hybrid genotypes in three kinds of breeding habitats: natural vernal pools, ephemeral man-made cattle ponds, and perennial man-made ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond, even in cases where perennial and seasonal ponds are within a few hundred meters. Thus, the hybrid zone has a mosaic structure that depends on pond hydrology or ecology. The presence of some broadly acting constraints on admixture is suggested by linkage disequilibria between physically unlinked molecular markers within ponds. In addition, we found several marker-specific deviations from Hardy-Weinberg equilibrium. One marker showed a consistent deficit of heterozygotes across pond types. Another showed heterozygote deficits only in vernal pools. A third was more likely to have heterozygote excess in ephemeral cattle ponds. These patterns indicate that admixture is influenced by complex genotype-by-environment interactions. [source] Quasispecies analysis of novel HIV-1 recombinants of subtypes A and G reveals no similarity to the mosaic structure of CRF02_AG,JOURNAL OF MEDICAL VIROLOGY, Issue 9 2007Rebecca L.R. Powell Abstract HIV-1 circulating recombinant form (CRF) 02_AG is responsible for greater than 65% of HIV-1 infections in Cameroon and is widespread across West and West-Central Africa. The parental subtypes A1 and G cocirculate in this part of Africa, and high rates of infection predispose to the generation of AG unique recombinant forms (URFs). Little is known as to whether A1 and G can recombine and thrive in vivo with breakpoints other than those characteristic of CRF02_AG. In this study, six unique recombinant viruses of subtypes A1 and G were identified in two individuals in Cameroon. A 1.5 kb fragment of the reverse transcriptase (RT) region of pol (HXB2 location 2,612,4,159) and the entire env gene (HXB2 location 6,202,9,096) were evaluated by phylogenetic and breakpoint analyses. Each URF was found to have breakpoints different than CRF02_AG, indicating that A and G gene segments are functionally compatible with more than one pattern of recombination. Furthermore, contemporaneous, cultured viruses from these individuals were analyzed, revealing different proportions of URFs compared to those found in plasma, possibly indicating compart mentalization and/or phenotypic variation among the URFs. CRF02_AG emerged from West-Central Africa to become a highly successful viral strain. As such, monitoring the spread of newly emerging AG recombinants is critical not only for understanding the epidemiology of HIV-1, but also in the design of future therapeutics and vaccines appropriate to this part of Africa, and globally. J. Med. Virol. 79:1270,1285, 2007. © Wiley-Liss, Inc. [source] Spatial dynamics of regeneration in a conifer/broad-leaved forest in northern JapanJOURNAL OF VEGETATION SCIENCE, Issue 5 2000Yasuhiro Kubota Ohwi (1972) Abstract. This study deals with stand dynamics over a 6-yr period in a conifer/broad-leaved mixed forest in Hokkaido, northern Japan. The annual rates of gap formation and recovery were 81.3 m2/ha and 66.7 m2/ha, respectively and turnover time of the canopy was 125 yr. The recruitment processes of the component species in this cool-temperate forest were governed by different canopy types: gap, canopy edge and closed canopy. Magnolia obovata regenerated in canopy edges, and Acer mono and Prunus ssiori regenerated in canopy edges and gaps. The results suggested that the mosaic structure made up of closed canopy, canopy edge and gap was related to various regeneration niches. Abies sachalinensis had high mortality rates, initiating gap expansion. The transition probabilities from closed canopy or canopy edge to gap for deciduous broad-leaved trees were lower than for A. sachalinensis, which implies that the difference in degeneration patterns of conifer and broad-leaved canopies contributes to the heterogeneity of spatial structure in the mixed forests. Spatial dynamics were determined by a combination of gap expansion by A. sachalinensis (neighbour-dependent disturbance) and gap formation by deciduous broad-leaved trees (random disturbance). [source] Degradation of blue LEDs related to structural disorderPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006A. V. Kamanin Abstract The degradation of blue light emitting diodes (LEDs) with different structural disorder based on MQW InGaN/GaN grown by MOCVD on sapphire has been investigated. New approach to analyze the degradation has been used. It takes into account the structural disorder determined by the extended defect system relaxation and related with poor coalescence of the mosaic structure domains. The results obtained leads to assumption that the migration and segregations of Ga on domain dislocation boundaries of the mosaic structure and the change of energy activation of Mg related centers are important reasons of degradation for all types of LEDs The fastest degradation for poor ordered LEDs was observed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] EBIC Characterization of III,Nitride Structures Using Multifractal ParameterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003N.M. Shmidt Abstract Use of electron beam induced current (EBIC) method in combination of the multifractal analysis for investigation of GaN epitaxial layers with different degree of order of mosaic structure has revealed basic difference in distribution of extended defects with intense nonradiative recombination and small diffusion length of about 0.1 ,m. The diffusion length of the layers with well ordered mosaic structure was determined to be 1.5,2 times longer than that of the layers with less-ordered mosaic structure. The difference between the extended defect distributions well correlates with peculiarities of carrier transfer in these layers. [source] | ||||||||||