19 research outputs found
Seed Mass and Morphology in Outcrossing and Selfing Species of Clarkia (Onagraceae): An SEM Study
Seeds from three pairs of outcrossing-selfing sister taxa from the genus Clarkia (farewell-to-spring, Onagraceae)âClarkia unguiculata, Clarkia exilis, Clarkia xantiana ssp. xantiana and ssp. parviflora, and Clarkia concinna ssp. concinna and ssp. automixaâwere studied to assess the effects of contrasting mating systems on seed mass and seed morphology. For each outcrossing-selfing comparison, the seed mass of the selfing taxon was less than that of the outcrossing taxon. Seed mass typically differed significantly among populations within a taxon. Scanning electron microscopy showed that the seeds from all these taxa share several characteristics: a bullet to shield shape, a reticulate exotesta pattern, presence of crystals in the seed coat, and a seed coat that varies in thickness over the length of the seed. No morphological feature reliably distinguished seeds of outcrossing taxa from those of selfing taxa. The lack of morphological differences in conjunction with the consistent differences in seed mass between selfing and outcrossing seeds in these taxa supports the hypothesis that evolutionary forces have acted only on seed mass and not on seed morphology
Genome Sequences of Erwinia Phyllophages AH04 and AH06
Although crucial in shaping bacterial communities, few bacteriophages of the phyllosphere have been described. We provide genome data for two Myoviridae phages, AH04 and AH06, isolated on Erwinia billingiae strains. AH04 shares limited genetic similarity with previously described phages, while AH06 shares over 75% similarity with various Erwinia phages
Complete Genome Sequence of the Pantoea Phage AH07
Bacteriophages of the phyllosphere have not been extensively described, despite their role in bacterial communities on this plant organ. Here, we describe a temperate Pantoea phage, AH07, that was isolated from the leaves of horse chestnut trees. The 37,859-bp linear double-stranded DNA genome contains 58 putative genes, including an integration cassette
Complete Genome Sequences of Four Phages of the Horse Chestnut Phyllosphere
Bacteriophages play important roles in determining bacterial communities, including plant microbiota. Here, we describe four lytic phages, three Siphoviridae and one Podoviridae, isolated from four different bacterial species found on the leaves of horse chestnut trees. Their double-stranded DNA (dsDNA) genomes range from 39,095 to 46,062âbp and contain 51 to 70 genes
Course-based Science Research Promotes Learning in Diverse Students at Diverse Institutions
Course-based research experiences (CREs) are powerful strategies for spreading learning and improving persistence for all students, both science majors and nonscience majors. Here we address the crucial components of CREs (context, discovery, ownership, iteration, communication, presentation) found across a broad range of such courses at a variety of academic institutions. We also address how the design of a CRE should vary according to the background of student participants; no single CRE format is perfect. We provide a framework for implementing CREs across multiple institutional types and several disciplines throughout the typical four years of undergraduate work, designed to a variety of student backgrounds. Our experiences implementing CREs also provide guidance on overcoming barriers to their implementation
Friesian horses as a possible model for human acquired aortopulmonary fistulation
BACKGROUND: Acquired aortopulmonary fistulation is a rare condition in humans. It usually results as a late complication of a true or pseudoaneurysm of the thoracic aorta. It is most commonly associated with trauma or surgery, less commonly with atherosclerosis, inflammation, hypertension or Marfan's syndrome. Aortopulmonary fistulation is also seen as a rare complication of acute aortic dissection. On rare occasions, acquired aortopulmonary fistulation is reported in aged patients without any of the above mentioned triggering factors. Thus, these cases should be considered as idiopathic aortopulmonary fistulation. Clearly, the pathogenesis of this condition is not yet completely understood. Friesian horses are highly inbred and are affected by several genetic conditions. Rupture of the thoracic aorta has a relatively high prevalence in Friesian horses and is often characterized by the formation of a pseudoaneurysm with subsequent fistulation into the pulmonary artery. Affected animals may survive for several weeks to months. FINDINGS: Here we performed vascular casting in three affected Friesian horses. In all three cases, an aortic rupture at the caudoventral side of the aorta was connected with a rupture of the main pulmonary artery just proximal to its bifurcation. CONCLUSIONS: Affected Friesians show a consistent location and configuration of the aortic rupture site, very similar to the human condition and therefore could act as a spontaneous model to study this disease
Complete Genome Sequences of Two Temperate Bacillus subtilis Phages Isolated at Tumamoc Hill Desert Laboratory
Bacteriophages are important in structuring bacterial communities, including desert soils dominated by Bacillus species. Here, we describe two genetically similar temperate phages isolated on a Bacillus subtilis strain from soil in Tucson, Arizona. Their double-stranded DNA (dsDNA) genomes contain 98 and 102 genes, with a set of 4 genes being found in only one phage
Cluster M Mycobacteriophages Bongo, PegLeg, and Rey with Unusually Large Repertoires of tRNA Isotopes
Genomic analysis of a large set of phages infecting the common hostMycobacterium smegmatis mc2155 shows that they span considerable genetic diversity. There are more than 20 distinct types that lack nucleotide similarity with each other, and there is considerable diversity within most of the groups. Three newly isolated temperate mycobacteriophages, Bongo, PegLeg, and Rey, constitute a new group (cluster M), with the closely related phages Bongo and PegLeg forming subcluster M1 and the more distantly related Rey forming subcluster M2. The cluster M mycobacteriophages have siphoviral morphologies with unusually long tails, are homoimmune, and have larger than average genomes (80.2 to 83.7 kbp). They exhibit a variety of features not previously described in other mycobacteriophages, including noncanonical genome architectures and several unusual sets of conserved repeated sequences suggesting novel regulatory systems for both transcription and translation. In addition to containing transfer-messenger RNA and RtcB-like RNA ligase genes, their genomes encode 21 to 24 tRNA genes encompassing complete or nearly complete sets of isotypes. We predict that these tRNAs are used in late lytic growth, likely compensating for the degradation or inadequacy of host tRNAs. They may represent a complete set of tRNAs necessary for late lytic growth, especially when taken together with the apparent lack of codons in the same late genes that correspond to tRNAs that the genomes of the phages do not obviously encode
«La relation de limitation et dâexception dans le français dâaujourdâhui : exceptĂ©, sauf et hormis comme pivots dâune relation algĂ©brique »
Lâanalyse des emplois prĂ©positionnels et des emplois conjonctifs dâ âexceptĂ©â, de âsaufâ et dâ âhormisâ permet dâenvisager les trois prĂ©positions/conjonctions comme le pivot dâun binĂŽme, comme la plaque tournante dâune structure bipolaire. PlacĂ©es au milieu du binĂŽme, ces prĂ©positions sont forcĂ©es par leur sĂ©mantisme originaire dĂ»ment mĂ©taphorisĂ© de jouer le rĂŽle de marqueurs dâinconsĂ©quence systĂ©matique entre lâĂ©lĂ©ment se trouvant Ă leur gauche et celui qui se trouve Ă leur droite. Lâopposition qui surgit entre les deux Ă©lĂ©ments nâest donc pas une incompatibilitĂ© naturelle, intrinsĂšque, mais extrinsĂšque, induite. Dans la plupart des cas (emplois limitatifs), cette opposition prend la forme dâun rapport entre une « classe » et le « membre (soustrait) de la classe », ou bien entre un « tout » et une « partie » ; dans dâautres (emplois exceptifs), cette opposition se manifeste au contraire comme une attaque de front portĂ©e par un « tout » Ă un autre « tout ». De plus, lâinconsĂ©quence induite mise en place par la prĂ©position/conjonction paraĂźt, en principe, tout Ă fait insurmontable. Dans lâassertion « les Ă©cureuils vivent partout, sauf en Australie » (que lâon peut expliciter par « Les Ă©cureuils vivent partout, sauf [quâils ne vivent pas] en Australie »), la prĂ©position semble en effet capable dâimpliquer le prĂ©dicat principal avec signe inverti, et de bĂątir sur une telle implication une sorte de sous Ă©noncĂ© qui, Ă la rigueur, est totalement inconsĂ©quent avec celui qui le prĂ©cĂšde (si « les Ă©cureuils ne vivent pas en Australie », le fait quâils « vivent partout » est faux). NĂ©anmoins, lâanalyse montre quâalors que certaines de ces oppositions peuvent enfin ĂȘtre dĂ©passĂ©es, dâautres ne le peuvent pas. Câest, respectivement, le cas des relations limitatives et des relations exceptives. La relation limitative, impliquant le rapport « tout » - « partie », permet de rĂ©soudre le conflit dans les termes dâune somme algĂ©brique entre deux sous Ă©noncĂ©s pourvus de diffĂ©rent poids informatif et de signe contraire. Les valeurs numĂ©riques des termes de la somme Ă©tant dĂ©sĂ©quilibrĂ©es, le rĂ©sultat est toujours autre que zĂ©ro. La relation exceptive, au contraire, qui nâimplique pas le rapport « tout » - « partie », nâest pas capable de rĂ©soudre le conflit entre deux sous Ă©noncĂ©s pourvus du mĂȘme poids informatif et en mĂȘme temps de signe contraire : les valeurs numĂ©riques des termes de la somme Ă©tant symĂ©triques et Ă©gales, le rĂ©sultat sera toujours Ă©quivalent Ă zĂ©ro
Testing Hypotheses for the Presence of the tRNA Genes in Mycobacteriophage Genomes
The presence of tRNA genes in bacteriophages has been explained on the basis of codon usage (tRNA genes are retained in the phage genome if they correspond to codons more common in the phage than in its host) or amino acid usage (independent of codon, the amino acid corresponding to the retained tRNA gene is more common in the phage genome than in the bacterial host). The existence of a large database of sequenced mycobacteriophages, isolated on the common host Mycobacterium smegmatis, allows us to test the above hypotheses as well as explore other hypotheses for the presence of tRNA genes. Our analyses suggest that amino acid rather than codon usage better explains the presence of tRNA genes in mycobacteriophages. However, closely related phages that differ in the presence of tRNA genes in their genomes are capable of lysing the common bacterial host and do not differ in codon or amino acid usage. This suggests that the benefits of having tRNA genes may be associated with either growth in the host or the ability to infect more hosts (i.e., host range) rather than simply infecting a particular host