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July 7, 2019

Hybrid de novo genome assembly of the Chinese herbal fleabane Erigeron breviscapus.

The plants in the Erigeron genus of the Compositae (Asteraceae) family are commonly called fleabanes, possibly due to the belief that certain chemicals in these plants repel fleas. In the traditional Chinese medicine, Erigeron breviscapus , which is native to China, was widely used in the treatment of cerebrovascular disease. A handful of bioactive compounds, including scutellarin, 3,5-dicaffeoylquinic acid, and 3,4-dicaffeoylquinic acid, have been isolated from the plant. With the purpose of finding novel medicinal compounds and understanding their biosynthetic pathways, we propose to sequence the genome of E. breviscapus . We assembled the highly heterozygous E. breviscapus genome using a combination of PacBio single-molecular real-time sequencing and next-generation sequencing methods on the Illumina HiSeq platform. The final draft genome is approximately 1.2 Gb, with contig and scaffold N50 sizes of 18.8 kb and 31.5 kb, respectively. Further analyses predicted 37 504 protein-coding genes in the E. breviscapus genome and 8172 shared gene families among Compositae species. The E. breviscapus genome provides a valuable resource for the investigation of novel bioactive compounds in this Chinese herb.

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July 7, 2019

Biosynthesis of 1a-hydroxycorticosterone in the winter skate Leucoraja ocellata: evidence to suggest a novel steroidogenic route.

The present study explores the ability of intracellular bacteria within the renal-inter-renal tissue of the winter skate Leucoraja ocellata to metabolize steroids and contribute to the synthesis of the novel elasmobranch corticosteroid, 1a-hydroxycorticosterone (1a-OH-B). Despite the rarity of C1 hydroxylation noted in the original identification of 1a-OH-B, literature provides evidence for steroid C1 hydroxylation by micro-organisms. Eight ureolytic bacterial isolates were identified in the renal-inter-renal tissue of L. ocellata, the latter being the site of 1a-OH-B synthesis. From incubations of bacterial isolates with known amounts of potential 1a-OH-B precursors, one isolate UM008 of the genus Rhodococcus was seen to metabolize corticosteroids and produce novel products via HPLC analysis. Cations Zn2+and Fe3+altered metabolism of certain steroid precursors, suggesting inhibition of Rhodococcus steroid catabolism. Genome sequencing of UM008 identified strong sequence and structural homology to that of Rhodococcus erythropolis PR4. A complete enzymatic pathway for steroid-ring oxidation as documented within other Actinobacteria was identified within the UM008 genome. This study highlights the potential role of Rhodococcus bacteria in steroid metabolism and proposes a novel alternative pathway for 1a-OH-B synthesis, suggesting a unique form of mutualism between intracellular bacteria and their elasmobranch host.© 2017 The Fisheries Society of the British Isles.

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July 7, 2019

Genome mining and predictive functional profiling of acidophilic rhizobacterium Pseudomonas fluorescens Pt14.

Pseudomonas fluorescens Pt14 is a non-pathogenic and acidophilic bacterium isolated from acidic soil (pH 4.65). Genome sequencing of strain Pt14 was performed using Single Molecule Real Time (SMRT) sequencing to get insights into unique existence of this strain in acidic environment. Complete genome sequence of this strain revealed a chromosome of 5,841,722 bp having 5354 CDSs and 88 RNAs. Phylogenomic reconstruction based on 16S rRNA gene, Average Nucleotide Identity (ANI) values and marker proteins revealed that strain Pt14 shared a common clade with P. fluorescens strain A506 and strain SS101. ANI value of strain Pt14 in relation to strain A506 was found 99.23% demonstrating a very close sub-species association at genome level. Further, orthology determination among these three phylogenetic neighbors revealed 4726 core proteins. Functional analysis elucidated significantly higher abundance of sulphur metabolism (>1×) which could be one of the reasons for the survival of strain Pt14 under acidic conditions (pH 4.65). Acidophilic bacteria have capability to oxidize sulphur into sulphuric acid which in turn can make the soil acidic and genome-wide analysis of P. fluorescens Pt14 demonstrated that this strain contributes towards making the soil acidic.

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July 7, 2019

MHC class I diversity in chimpanzees and bonobos.

Major histocompatibility complex (MHC) class I genes are critically involved in the defense against intracellular pathogens. MHC diversity comparisons among samples of closely related taxa may reveal traces of past or ongoing selective processes. The bonobo and chimpanzee are the closest living evolutionary relatives of humans and last shared a common ancestor some 1 mya. However, little is known concerning MHC class I diversity in bonobos or in central chimpanzees, the most numerous and genetically diverse chimpanzee subspecies. Here, we used a long-read sequencing technology (PacBio) to sequence the classical MHC class I genes A, B, C, and A-like in 20 and 30 wild-born bonobos and chimpanzees, respectively, with a main focus on central chimpanzees to assess and compare diversity in those two species. We describe in total 21 and 42 novel coding region sequences for the two species, respectively. In addition, we found evidence for a reduced MHC class I diversity in bonobos as compared to central chimpanzees as well as to western chimpanzees and humans. The reduced bonobo MHC class I diversity may be the result of a selective process in their evolutionary past since their split from chimpanzees.

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July 7, 2019

Metabolic modeling of energy balances in Mycoplasma hyopneumoniae shows that pyruvate addition increases growth rate.

Mycoplasma hyopneumoniae is cultured on large-scale to produce antigen for inactivated whole-cell vaccines against respiratory disease in pigs. However, the fastidious nutrient requirements of this minimal bacterium and the low growth rate make it challenging to reach sufficient biomass yield for antigen production. In this study, we sequenced the genome of M. hyopneumoniae strain 11 and constructed a high quality constraint-based genome-scale metabolic model of 284 chemical reactions and 298 metabolites. We validated the model with time-series data of duplicate fermentation cultures to aim for an integrated model describing the dynamic profiles measured in fermentations. The model predicted that 84% of cellular energy in a standard M. hyopneumoniae cultivation was used for non-growth associated maintenance and only 16% of cellular energy was used for growth and growth associated maintenance. Following a cycle of model-driven experimentation in dedicated fermentation experiments, we were able to increase the fraction of cellular energy used for growth through pyruvate addition to the medium. This increase in turn led to an increase in growth rate and a 2.3 times increase in the total biomass concentration reached after 3-4 days of fermentation, enhancing the productivity of the overall process. The model presented provides a solid basis to understand and further improve M. hyopneumoniae fermentation processes. Biotechnol. Bioeng. 2017;114: 2339-2347. © 2017 Wiley Periodicals, Inc.© 2017 Wiley Periodicals, Inc.

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July 7, 2019

Complete genome sequence of a Legionella longbeachae serogroup 1 strain isolated from a patient with Legionnaires’ disease.

Legionella longbeachae serogroup 1, predominantly found in soil and composted plant material, causes the majority of cases of Legionnaires’ disease (LD) in New Zealand. Here, we report the complete genome sequence of an L. longbeachae serogroup 1 (sg1) isolate derived from a patient hospitalized with LD in Christchurch, New Zealand. Copyright © 2017 Slow et al.

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July 7, 2019

No evidence for maintenance of a sympatric Heliconius species barrier by chromosomal inversions.

Mechanisms that suppress recombination are known to help maintain species barriers by preventing the breakup of coadapted gene combinations. The sympatric butterfly species Heliconius melpomene and Heliconius cydno are separated by many strong barriers, but the species still hybridize infrequently in the wild, and around 40% of the genome is influenced by introgression. We tested the hypothesis that genetic barriers between the species are maintained by inversions or other mechanisms that reduce between-species recombination rate. We constructed fine-scale recombination maps for Panamanian populations of both species and their hybrids to directly measure recombination rate within and between species, and generated long sequence reads to detect inversions. We find no evidence for a systematic reduction in recombination rates in F1 hybrids, and also no evidence for inversions longer than 50 kb that might be involved in generating or maintaining species barriers. This suggests that mechanisms leading to global or local reduction in recombination do not play a significant role in the maintenance of species barriers between H. melpomene and H. cydno.

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July 7, 2019

Genome-wide analysis of gene expression and protein secretion of Babesia canis during virulent infection identifies potential pathogenicity factors.

Infections of dogs with virulent strains of Babesia canis are characterized by rapid onset and high mortality, comparable to complicated human malaria. As in other apicomplexan parasites, most Babesia virulence factors responsible for survival and pathogenicity are secreted to the host cell surface and beyond where they remodel and biochemically modify the infected cell interacting with host proteins in a very specific manner. Here, we investigated factors secreted by B. canis during acute infections in dogs and report on in silico predictions and experimental analysis of the parasite’s exportome. As a backdrop, we generated a fully annotated B. canis genome sequence of a virulent Hungarian field isolate (strain BcH-CHIPZ) underpinned by extensive genome-wide RNA-seq analysis. We find evidence for conserved factors in apicomplexan hemoparasites involved in immune-evasion (e.g. VESA-protein family), proteins secreted across the iRBC membrane into the host bloodstream (e.g. SA- and Bc28 protein families), potential moonlighting proteins (e.g. profilin and histones), and uncharacterized antigens present during acute crisis in dogs. The combined data provides a first predicted and partially validated set of potential virulence factors exported during fatal infections, which can be exploited for urgently needed innovative intervention strategies aimed at facilitating diagnosis and management of canine babesiosis.

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July 7, 2019

Isolation of a novel ‘atypical’ Brucella strain from a bluespotted ribbontail ray (Taeniura lymma).

A pleomorphic Gram-negative, motile coccobacillus was isolated from the gills of a wild-caught bluespotted ribbontail ray after its sudden death during quarantine. Strain 141012304 was observed to grow aerobically, to be clearly positive for cytochrome oxidase, catalase, urease and was initially identified as “Brucella melitensis” or “Ochrobactrum anthropi” by Matrix-assisted laser desorption/ionization-time of flight mass spectrometry and VITEK2-compact(®), respectively. Affiliation to the genus Brucella was confirmed by bcsp31 and IS711 PCR as well as by Brucella species-specific multiplex PCR, therein displaying a characteristic banding pattern recently described for Brucella strains obtained from amphibian hosts. Likewise, based on recA sequencing, strain 141012304 was found to form a separate lineage, within the so called ‘atypical’ Brucella, consisting of genetically more distantly related strains. The closest similarity was detected to brucellae, which have recently been isolated from edible bull frogs. Subsequent next generation genome sequencing and phylogenetic analysis confirmed that the ray strain represents a novel Brucella lineage within the atypical group of Brucella and in vicinity to Brucella inopinata and Brucella strain BO2, both isolated from human patients. This is the first report of a natural Brucella infection in a saltwater fish extending the host range of this medically important genus.

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July 7, 2019

Loss of pollen-specific phospholipase NOT LIKE DAD triggers gynogenesis in maize.

Gynogenesis is an asexual mode of reproduction common to animals and plants, in which stimuli from the sperm cell trigger the development of the unfertilized egg cell into a haploid embryo. Fine mapping restricted a major maize QTL (quantitative trait locus) responsible for the aptitude of inducer lines to trigger gynogenesis to a zone containing a single gene NOT LIKE DAD (NLD) coding for a patatin-like phospholipase A. In all surveyed inducer lines, NLD carries a 4-bp insertion leading to a predicted truncated protein. This frameshift mutation is responsible for haploid induction because complementation with wild-type NLD abolishes the haploid induction capacity. Activity of the NLD promoter is restricted to mature pollen and pollen tube. The translational NLD::citrine fusion protein likely localizes to the sperm cell plasma membrane. In Arabidopsis roots, the truncated protein is no longer localized to the plasma membrane, contrary to the wild-type NLD protein. In conclusion, an intact pollen-specific phospholipase is required for successful sexual reproduction and its targeted disruption may allow establishing powerful haploid breeding tools in numerous crops.© 2017 The Authors.

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July 7, 2019

Evolution and comparative genomics of pAQU-like conjugative plasmids in Vibrio species.

To investigate a set of MDR conjugative plasmids found in Vibrio species and characterize the underlying evolution process.pAQU-type plasmids from Vibrio species were sequenced using both Illumina and PacBio platforms. Bioinformatics tools were utilized to analyse the typical MDR regions and core genes in the plasmids.The nine pAQU-type plasmids ranged from ~160 to 206?kb in size and were found to harbour as many as 111 core genes encoding conjugative, replication and maintenance functions. Eight plasmids were found to carry a typical MDR region, which contained various accessory and resistance genes, including ISCR1-blaPER-1-bearing complex class 1 integrons, ISCR2-floR, ISCR2-tet(D)-tetR-ISCR2, qnrVC6, a Tn10-like structure and others associated with mobile elements. Comparison between a plasmid without resistance genes and different MDR plasmids showed that integration of different mobile elements, such as IS26, ISCR1, ISCR2, IS10 and IS6100, into the plasmid backbone was the key mechanism by which foreign resistance genes were acquired during the evolution process.This study identified pAQU-type plasmids as emerging MDR conjugative plasmids among important pathogens from different origins in Asia. These findings suggest that aquatic bacteria constitute a major reservoir of resistance genes, which may be transmissible to other human pathogens during food production and processing.© The Author 2017. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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July 7, 2019

De novo yeast genome assemblies from MinION, PacBio and MiSeq platforms.

Long-read sequencing technologies such as Pacific Biosciences and Oxford Nanopore MinION are capable of producing long sequencing reads with average fragment lengths of over 10,000 base-pairs and maximum lengths reaching 100,000 base- pairs. Compared with short reads, the assemblies obtained from long-read sequencing platforms have much higher contig continuity and genome completeness as long fragments are able to extend paths into problematic or repetitive regions. Many successful assembly applications of the Pacific Biosciences technology have been reported ranging from small bacterial genomes to large plant and animal genomes. Recently, genome assemblies using Oxford Nanopore MinION data have attracted much attention due to the portability and low cost of this novel sequencing instrument. In this paper, we re-sequenced a well characterized genome, the Saccharomyces cerevisiae S288C strain using three different platforms: MinION, PacBio and MiSeq. We present a comprehensive metric comparison of assemblies generated by various pipelines and discuss how the platform associated data characteristics affect the assembly quality. With a given read depth of 31X, the assemblies from both Pacific Biosciences and Oxford Nanopore MinION show excellent continuity and completeness for the 16 nuclear chromosomes, but not for the mitochondrial genome, whose reconstruction still represents a significant challenge.

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July 7, 2019

IncFII conjugative plasmid-mediated transmission of blaNDM-1 elements among animal-borne Escherichia coli strains.

This study aims to investigate the prevalence and transmission dynamics of the blaNDM-1 gene in animal Escherichia coli strains. Two IncFII blaNDM-1-encoding plasmids with only minor structural variation in the MDR region, pHNEC46-NDM and pHNEC55-NDM, were found to be responsible for the transmission of blaNDM-1 in these strains. The blaNDM-1 gene can be incorporated into plasmids and stably inherited in animal-borne E. coli strains that can be maintained in animal gut microflora even without carbapenem selection pressure. Copyright © 2016 American Society for Microbiology.

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July 7, 2019

Higher-order organisation of extremely amplified, potentially functional and massively methylated 5S rDNA in European pikes (Esox sp.).

Pikes represent an important genus (Esox) harbouring a pre-duplication karyotype (2n?=?2x?=?50) of economically important salmonid pseudopolyploids. Here, we have characterized the 5S ribosomal RNA genes (rDNA) in Esox lucius and its closely related E. cisalpinus using cytogenetic, molecular and genomic approaches. Intragenomic homogeneity and copy number estimation was carried out using Illumina reads. The higher-order structure of rDNA arrays was investigated by the analysis of long PacBio reads. Position of loci on chromosomes was determined by FISH. DNA methylation was analysed by methylation-sensitive restriction enzymes.The 5S rDNA loci occupy exclusively (peri)centromeric regions on 30-38 acrocentric chromosomes in both E. lucius and E. cisalpinus. The large number of loci is accompanied by extreme amplification of genes (>20,000 copies), which is to the best of our knowledge one of the highest copy number of rRNA genes in animals ever reported. Conserved secondary structures of predicted 5S rRNAs indicate that most of the amplified genes are potentially functional. Only few SNPs were found in genic regions indicating their high homogeneity while intergenic spacers were more heterogeneous and several families were identified. Analysis of 10-30 kb-long molecules sequenced by the PacBio technology (containing about 40% of total 5S rDNA) revealed that the vast majority (96%) of genes are organised in large several kilobase-long blocks. Dispersed genes or short tandems were less common (4%). The adjacent 5S blocks were directly linked, separated by intervening DNA and even inverted. The 5S units differing in the intergenic spacers formed both homogeneous and heterogeneous (mixed) blocks indicating variable degree of homogenisation between the loci. Both E. lucius and E. cisalpinus 5S rDNA was heavily methylated at CG dinucleotides.Extreme amplification of 5S rRNA genes in the Esox genome occurred in the absence of significant pseudogenisation suggesting its recent origin and/or intensive homogenisation processes. The dense methylation of units indicates that powerful epigenetic mechanisms have evolved in this group of fish to silence amplified genes. We discuss how the higher-order repeat structures impact on homogenisation of 5S rDNA in the genome.

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