Samsun Sung

Genome Scanning for Conditionally Essential Genes in Salmonella enterica Serotype Typhimurium

ABSTRACT As more whole-genome sequences become available, there is an increasing demand for high-throughput methods that link genes to phenotypes, facilitating discovery of new gene functions. In this study, we describe a new version of the Tn-seq method involving a modified EZ:Tn5 transposon for genome-wide and quantitative mapping of all insertions in a complex mutant library utilizing massively parallel Illumina sequencing. This Tn-seq method was applied to a genome-saturating Salmonella enterica serotype Typhimurium mutant library recovered from selection under 3 different in vitro growth conditions (diluted Luria-Bertani [LB] medium, LB medium plus bile acid, and LB medium at 42°C), mimicking some aspects of host stressors. We identified an overlapping set of 105 protein-coding genes in S. Typhimurium that are conditionally essential under at least one of the above selective conditions. Competition assays using 4 deletion mutants (pyrD, glnL, recD, and STM14_5307) confirmed the phenotypes predicted by Tn-seq data, validating the utility of this approach in discovering new gene functions. With continuously increasing sequencing capacity of next generation sequencing technologies, this robust Tn-seq method will aid in revealing unexplored genetic determinants and the underlying mechanisms of various biological processes in Salmonella and the other approximately 70 bacterial species for which EZ:Tn5 mutagenesis has been established.

Facile preparation of reduced graphene oxide-based gas barrier films for organic photovoltaic devices

Reduced graphene oxide-based films were prepared to assess their effects as gas barriers on the stability of organic photovoltaic (OPV) devices. The direct spin-casting of a graphene oxide suspension onto an aluminum electrode was performed to encapsulate the associated OPV device with a reduced graphene oxide film. The lifetime of the OPV device after the reduction process was found to be increased by a factor of 50. The gas barrier properties of a graphene oxide layer are closely related to its surface roughness and dispersibility. Furthermore, these gas barrier properties can be enhanced by controlling the thermal reduction conditions. The thermal reduction of a graphene oxide film at a low heating rate results in a low water vapor permeability, only 0.1% of that of an as-prepared polyethylene naphthalate film. These results indicate that the dispersibility, surface roughness, and reduction conditions of a graphene oxide film significantly influence its gas barrier performance. Further investigations of the reduction of graphene oxide films are expected to enable further improvements in performance.

The genome landscape of indigenous African cattle

BackgroundThe history of African indigenous cattle and their adaptation to environmental and human selection pressure is at the root of their remarkable diversity. Characterization of this diversity is an essential step towards understanding the genomic basis of productivity and adaptation to survival under African farming systems.ResultsWe analyze patterns of African cattle genetic variation by sequencing 48 genomes from five indigenous populations and comparing them to the genomes of 53 commercial taurine breeds. We find the highest genetic diversity among African zebu and sanga cattle. Our search for genomic regions under selection reveals signatures of selection for environmental adaptive traits. In particular, we identify signatures of selection including genes and/or pathways controlling anemia and feeding behavior in the trypanotolerant N’Dama, coat color and horn development in Ankole, and heat tolerance and tick resistance across African cattle especially in zebu breeds.ConclusionsOur findings unravel at the genome-wide level, the unique adaptive diversity of African cattle while emphasizing the opportunities for sustainable improvement of livestock productivity on the continent.

A genome-wide scan for signatures of directional selection in domesticated pigs

BackgroundAnimal domestication involved drastic phenotypic changes driven by strong artificial selection and also resulted in new populations of breeds, established by humans. This study aims to identify genes that show evidence of recent artificial selection during pig domestication.ResultsWhole-genome resequencing of 30 individual pigs from domesticated breeds, Landrace and Yorkshire, and 10 Asian wild boars at ~16-fold coverage was performed resulting in over 4.3 million SNPs for 19,990 genes. We constructed a comprehensive genome map of directional selection by detecting selective sweeps using an FST-based approach that detects directional selection in lineages leading to the domesticated breeds and using a haplotype-based test that detects ongoing selective sweeps within the breeds. We show that candidate genes under selection are significantly enriched for loci implicated in quantitative traits important to pig reproduction and production. The candidate gene with the strongest signals of directional selection belongs to group III of the metabolomics glutamate receptors, known to affect brain functions associated with eating behavior, suggesting that loci under strong selection include loci involved in behaviorial traits in domesticated pigs including tameness.ConclusionsWe show that a significant proportion of selection signatures coincide with loci that were previously inferred to affect phenotypic variation in pigs. We further identify functional enrichment related to behavior, such as signal transduction and neuronal activities, for those targets of selection during domestication in pigs.

An approach of orthology detection from homologous sequences under minimum evolution.

In the field of phylogenetics and comparative genomics, it is important to establish orthologous relationships when comparing homologous sequences. Due to the slight sequence dissimilarity between orthologs and paralogs, it is prone to regarding paralogs as orthologs. For this reason, several methods based on evolutionary distance, phylogeny and BLAST have tried to detect orthologs with more precision. Depending on their algorithmic implementations, each of these methods sometimes has increased false negative or false positive rates. Here, we developed a novel algorithm for orthology detection that uses a distance method based on the phylogenetic criterion of minimum evolution. Our algorithm assumes that sets of sequences exhibiting orthologous relationships are evolutionarily less costly than sets that include one or more paralogous relationships. Calculation of evolutionary cost requires the reconstruction of a neighbor-joining (NJ) tree, but calculations are unaffected by the topology of any given NJ tree. Unlike tree reconciliation, our algorithm appears free from the problem of incorrect topologies of species and gene trees. The reliability of the algorithm was tested in a comparative analysis with two other orthology detection methods using 95 manually curated KOG datasets and 21 experimentally verified EXProt datasets. Sensitivity and specificity estimates indicate that the concept of minimum evolution could be valuable for the detection of orthologs.

The Pig Genome Database (PiGenome): an integrated database for pig genome research

We established the Pig Genome Database (PiGenome) for pig genome research. The PiGenome integrates and analyzes all publicly available genome-wide data on pigs, including UniGenes, sequence tagged sites (STS) markers, quantitative trait loci (QTLs) data, and bacterial artificial chromosome (BAC) contigs. In addition, we produced 69,545 expressed sequence tags (ESTs) from the full-length enriched cDNA libraries of six tissues and 182 BAC contig sequences, which are also included in the database. QTLs, genetic markers, and BAC end-sequencing information were collected from public databases. The full-length enriched EST data were clustered and assembled into unique sequences, contigs, and singletons. The PiGenome provides functional annotation, identification of transcripts, mapping of coding sequences, and SNP information. It also provides an advanced search interface, a disease browser, alternative-splicing events, and a comparative gene map of the pig. A graphical map view and genome browser can map ESTs, contigs, BAC contigs (from the National Institute of Animal Science), Sino-Danish Pig Genome Project transcripts, and UniGene onto pig genome sequences which include our 182 BAC contigs and publically available BAC sequences of the Wellcome Trust Sanger Institute. The PiGenome is accessible at http://pigenome.nabc.go.kr/.

HGTree: database of horizontally transferred genes determined by tree reconciliation

The HGTree database provides putative genome-wide horizontal gene transfer (HGT) information for 2472 completely sequenced prokaryotic genomes. This task is accomplished by reconstructing approximate maximum likelihood phylogenetic trees for each orthologous gene and corresponding 16S rRNA reference species sets and then reconciling the two trees under parsimony framework. The tree reconciliation method is generally considered to be a reliable way to detect HGT events but its practical use has remained limited because the method is computationally intensive and conceptually challenging. In this regard, HGTree (http://hgtree.snu.ac.kr) represents a useful addition to the biological community and enables quick and easy retrieval of information for HGT-acquired genes to better understand microbial taxonomy and evolution. The database is freely available and can be easily scaled and updated to keep pace with the rapid rise in genomic information.

Exploring the Genetic Signature of Body Size in Yucatan Miniature Pig

Since being domesticated about 10,000–12,000 years ago, domestic pigs (Sus scrofa domesticus) have been selected for traits of economic importance, in particular large body size. However, Yucatan miniature pigs have been selected for small body size to withstand high temperature environment and for laboratory use. This renders the Yucatan miniature pig a valuable model for understanding the evolution of body size. We investigate the genetic signature for selection of body size in the Yucatan miniature pig. Phylogenetic distance of Yucatan miniature pig was compared to other large swine breeds (Yorkshire, Landrace, Duroc and wild boar). By estimating the XP-EHH statistic using re-sequencing data derived from 70 pigs, we were able to unravel the signatures of selection of body size. We found that both selections at the level of organism, and at the cellular level have occurred. Selection at the higher levels include feed intake, regulation of body weight and increase in mass while selection at the molecular level includes cell cycle and cell proliferation. Positively selected genes probed by XP-EHH may provide insight into the docile character and innate immunity as well as body size of Yucatan miniature pig.

Genome sequence of pacific abalone (Haliotis discus hannai): the first draft genome in family Haliotidae

Abstract Background: Abalones are large marine snails in the family Haliotidae and the genus Haliotis belonging to the class Gastropoda of the phylum Mollusca. The family Haliotidae contains only one genus, Haliotis, and this single genus is known to contain several species of abalone. With 18 additional subspecies, the most comprehensive treatment of Haliotidae considers 56 species valid [1]. Abalone is an economically important fishery and aquaculture animal that is considered a highly prized seafood delicacy. The total global supply of abalone has increased 5-fold since the 1970s and farm production increased explosively from 50 mt to 103 464 mt in the past 40 years. Additionally, researchers have recently focused on abalone given their reported tumor suppression effect. However, despite the valuable features of this marine animal, no genomic information is available for the Haliotidae family and related research is still limited. To construct the H. discus hannai genome, a total of 580-G base pairs using Illumina and Pacbio platforms were generated with 322-fold coverage based on the 1.8-Gb estimated genome size of H. discus hannai using flow cytometry. The final genome assembly consisted of 1.86 Gb with 35 450 scaffolds (>2 kb). GC content level was 40.51%, and the N50 length of assembled scaffolds was 211 kb. We identified 29 449 genes using Evidence Modeler based on the gene information from ab initio prediction, protein homology with known genes, and transcriptome evidence of RNA-seq. Here we present the first Haliotidae genome, H. discus hannai, with sequencing data, assembly, and gene annotation information. This will be helpful for resolving the lack of genomic information in the Haliotidae family as well as providing more opportunities for understanding gastropod evolution.

A genome-wide identification of genes potentially associated with host specificity of Brucella species

Brucella species are facultative intracellular pathogenic α-Proteobacteria that can cause brucellosis in humans and domestic animals. The clinical and veterinary importance of the bacteria has led to well established studies on the molecular mechanisms of Brucella infection of host organisms. However, to date, no genome-wide study has scanned for genes related to the host specificity of Brucella spp. The majority of bacterial genes related to specific environmental adaptations such as host specificity are well-known to have evolved under positive selection pressure. We thus detected signals of positive selection for individual orthologous genes among Brucella genomes and identified genes related to host specificity. We first determined orthologous sets from seven completely sequenced Brucella genomes using the Reciprocal Best Hits (RBH). A maximum likelihood analysis based on the branch-site test was accomplished to examine the presence of positive selection signals, which was subsequently confirmed by phylogenetic analysis. Consequently, 12 out of 2,033 orthologous genes were positively selected by specific Brucella lineages, each of which belongs to a particular animal host. Extensive literature reviews revealed that half of these computationally identified genes are indeed involved in Brucella host specificity. We expect that this genome-wide approach based on positive selection may be reliably used to screen for genes related to environmental adaptation of a particular species and that it will provide a set of appropriate candidate genes.