The progenitors of type Ia supernovae in the semidetached binaries with red giant donors

Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs) for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed. A red-giant (RG) star has been suggested to be the mass donor of the exploding WD, named as the symbiotic channel. However, previous studies on the this channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically investigate the parameter space, Galactic rates and delay time distributions of SNe Ia from the symbiotic channel by employing a revised mass-transfer prescription. Methods. We adopted an integrated mass-transfer prescription to calculate the mass-transfer process from a RG star onto the WD. In this prescription, the mass-transfer rate varies with the local material states. Results. We evolved a large number of WD+RG systems, and found that the parameter space of WD+RG systems for producing SNe Ia is significantly enlarged. This channel could produce SNe Ia with intermediate and old ages, contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure

Insight into Dominant Cellulolytic Bacteria from Two Biogas Digesters and Their Glycoside Hydrolase Genes

<div><p>Diverse cellulolytic bacteria are essential for maintaining high lignocellulose degradation ability in biogas digesters. However, little was known about functional genes and gene clusters of dominant cellulolytic bacteria in biogas digesters. This is the foundation to understand lignocellulose degradation mechanisms of biogas digesters and apply these gene resource for optimizing biofuel production. A combination of metagenomic and 16S rRNA gene clone library methods was used to investigate the dominant cellulolytic bacteria and their glycoside hydrolase (GH) genes in two biogas digesters. The 16S rRNA gene analysis revealed that the dominant cellulolytic bacteria were strains closely related to <i>Clostridium straminisolvens</i> and an uncultured cellulolytic bacterium designated BG-1. To recover GH genes from cellulolytic bacteria in general, and BG-1 in particular, a refined assembly approach developed in this study was used to assemble GH genes from metagenomic reads; 163 GH-containing contigs ≥ 1 kb in length were obtained. Six recovered GH5 genes that were expressed in <i>E</i>. <i>coli</i> demonstrated multiple lignocellulase activities and one had high mannanase activity (1255 U/mg). Eleven fosmid clones harboring the recovered GH-containing contigs were sequenced and assembled into 10 fosmid contigs. The composition of GH genes in the 163 assembled metagenomic contigs and 10 fosmid contigs indicated that diverse GHs and lignocellulose degradation mechanisms were present in the biogas digesters. In particular, a small portion of BG-1 genome information was recovered by PhyloPythiaS analysis. The lignocellulase gene clusters in BG-1 suggested that it might use a possible novel lignocellulose degradation mechanism to efficiently degrade lignocellulose. Dominant cellulolytic bacteria of biogas digester possess diverse GH genes, not only in sequences but also in their functions, which may be applied for production of biofuel in the future.</p></div

The number of metagenomic reads and contigs assigned to different GH family.

<p>(a) The number of metagenomic reads assigned to the encoding genes of different GH family. (b) The number of contigs recovered from the metagenomic short reads by the refined assembly approach assigned to the encoding genes of different GH family. U1, U2 and U3 refer to unclassified α-L-arabinofuranosidase, unclassified xylosidase and unclassified α-amylase, respectively.</p

Eleven fosmid contigs assembled from sequences of fosmid clones harboring GH-containing contigs or BG-1 16S rRNA genes.

<p>¹Number of GH-containing contigs harbored in each fosmid contig.</p><p>²Due to contig FC3 contained BG-1 16S rRNA gene, it was assigned to BG-1.</p><p>³Due to presence of conserved cohesin domain in FC10F, it was unable to accurately bin metagenomic reads to FC10F and calculated depth of FC10F.</p><p>Eleven fosmid contigs assembled from sequences of fosmid clones harboring GH-containing contigs or BG-1 16S rRNA genes.</p

The characterization of six GH5 genes expressed in <i>E</i>.<i>coli</i>.

<p>¹Nearest neighbor represented nearest protein sequence for each GH5 genes.</p><p>²All activity assays were performed at pH7.4 and 50°C. The substrates used to determine activities of endoglucanase, mannanase, xylanase and exocellulase were CMC, locust bean gum, xylan (beechwood) and pNPC. The unit of enzyme activity is U/mg protein.</p><p>³Activity was not detected.</p><p>⁴Activity was less than 1 U/mg protein.</p><p>⁵Cel5 and Cel6 were also mentioned as man1 and en2 in elsewhere (Yan <i>et al</i>., 2013), but were not expressed before.</p><p>The characterization of six GH5 genes expressed in <i>E</i>.<i>coli</i>.</p

The most dominant OTUs and their compositions in the bacterial 16S rRNA gene clone libraries and metagenomes of Z7 and Z8.

<p>¹The identity of 16S rRNA genes between representative sequence of each dominant OTU and their nearest bacteria or type strains.</p><p>²Z7_PCR and Z8_PCR represent the proportion of each OTU in the 16S rRNA gene clone library of Z7 and Z8.</p><p>³Z7_META and Z8_META represent the proportion of each OTU in all the 16S rRNA genes recovered from Z7 and Z8 metagenomic data.</p><p>* Significant differential OTUs between Z7 and Z8 16S rRNA clone libraries were identified and filtered (q-value, <0.001) using STAMP (permutation test).</p><p>The most dominant OTUs and their compositions in the bacterial 16S rRNA gene clone libraries and metagenomes of Z7 and Z8.</p

The hypothetical lignocellulose degradation mechanism predicted from gene 34 to gene 61 in contig FC1 of BG-1.

<p>The 28 genes were predicted to encode two LacI family transcriptional regulators (purple), one GntR family transcriptional regulator (purple), PAS fold and methyl-accepting chemotaxis protein (light green), proteins of four different ABC transport system (green), six GHs (2GH5, Cel5 and Cel6; one GH9; one GH8; 2 GH2, GH2_1 and GH2_2) (red) and other functional proteins. The chemotaxis-like regulatory system described in the black box was inferred from other BG-1 genome information.</p

HAdV co-infections with common respiratory pathogens.

<p>HAdV co-infections with common respiratory pathogens.</p

Clinical manifestations and laboratory findings from hospitalized children infected with HAdV-3 and HAdV-7 in seasonal peaks, 2012–2013.

<p>Clinical manifestations and laboratory findings from hospitalized children infected with HAdV-3 and HAdV-7 in seasonal peaks, 2012–2013.</p

HAdV type distribution in hospitalized children with ARIs from July through September, 2012–2013.

<p>(A) HAdV type distribution from July through September in each year; (B) HAdV type distribution from July through September for the two years.</p