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September 22, 2019  |  

Draft genome of Glyptosternon maculatum, an endemic fish from Tibet Plateau.

Mechanisms for high-altitude adaption have attracted widespread interest among evolutionary biologists. Several genome-wide studies have been carried out for endemic vertebrates in Tibet, including mammals, birds, and amphibians. However, little information is available about the adaptive evolution of highland fishes. Glyptosternon maculatum (Regan 1905), also known as Regan or barkley and endemic to the Tibetan Plateau, belongs to the Sisoridae family, order Siluriformes (catfishes). This species lives at an elevation ranging from roughly 2,800 m to 4,200 m. Hence, a high-quality reference genome of G. maculatum provides an opportunity to investigate high-altitude adaption mechanisms of fishes.To obtain a high-quality reference genome sequence of G. maculatum, we combined Pacific Bioscience single-molecule real-time sequencing, Illumina paired-end sequencing, 10X Genomics linked-reads, and BioNano optical map techniques. In total, 603.99 Gb sequencing data were generated. The assembled genome was about 662.34 Mb with scaffold and contig N50 sizes of 20.90 Mb and 993.67 kb, respectively, which captured 83% complete and 3.9% partial vertebrate Benchmarking Universal Single-Copy Orthologs. Repetitive elements account for 35.88% of the genome, and ?22,066 protein-coding genes were predicted from the genome, of which 91.7% have been functionally annotated.We present the first comprehensive de novo genome of G. maculatum. This genetic resource is fundamental for investigating the origin of G. maculatum and will improve our understanding of high-altitude adaption of fishes. The assembled genome can also be used as reference for future population genetic studies of G. maculatum.


September 22, 2019  |  

Forward genetics by genome sequencing uncovers the central role of the Aspergillus niger goxB locus in hydrogen peroxide induced glucose oxidase expression.

Aspergillus niger is an industrially important source for gluconic acid and glucose oxidase (GOx), a secreted commercially important flavoprotein which catalyses the oxidation of ß-D-glucose by molecular oxygen to D-glucolactone and hydrogen peroxide. Expression of goxC, the GOx encoding gene and the concomitant two step conversion of glucose to gluconic acid requires oxygen and the presence of significant amounts of glucose in the medium and is optimally induced at pH 5.5. The molecular mechanisms underlying regulation of goxC expression are, however, still enigmatic. Genetic studies aimed at understanding GOx induction have indicated the involvement of at least seven complementation groups, for none of which the molecular basis has been resolved. In this study, a mapping-by-sequencing forward genetics approach was used to uncover the molecular role of the goxB locus in goxC expression. Using the Illumina and PacBio sequencing platforms a hybrid high quality draft genome assembly of laboratory strain N402 was obtained and used as a reference for mapping of genomic reads obtained from the derivative NW103:goxB mutant strain. The goxB locus encodes a thioredoxin reductase. A deletion of the encoding gene in the N402 parent strain led to a high constitutive expression level of the GOx and the lactonase encoding genes required for the two-step conversion of glucose in gluconic acid and of the catR gene encoding catalase R. This high constitutive level of expression was observed to be irrespective of the carbon source and oxidative stress applied. A model clarifying the role of GoxB in the regulation of the expression of goxC involving hydrogen peroxide as second messenger is presented.


September 22, 2019  |  

The pathogenic mechanisms of Tilletia horrida as revealed by comparative and functional genomics.

Tilletia horrida is a soil-borne, mononucleate basidiomycete fungus with a biotrophic lifestyle that causes rice kernel smut, a disease that is distributed throughout hybrid rice growing areas worldwide. Here we report on the high-quality genome sequence of T. horrida; it is composed of 23.2?Mb that encode 7,729 predicted genes and 6,973 genes supported by RNA-seq. The genome contains few repetitive elements that account for 8.45% of the total. Evolutionarily, T. horrida lies close to the Ustilago fungi, suggesting grass species as potential hosts, but co-linearity was not observed between T. horrida and the barley smut Ustilago hordei. Genes and functions relevant to pathogenicity were presumed. T. horrida possesses a smaller set of carbohydrate-active enzymes and secondary metabolites, which probably reflect the specific characteristics of its infection and biotrophic lifestyle. Genes that encode secreted proteins and enzymes of secondary metabolism, and genes that are represented in the pathogen-host interaction gene database genes, are highly expressed during early infection; this is consistent with their potential roles in pathogenicity. Furthermore, among the 131 candidate pathogen effectors identified according to their expression patterns and functionality, we validated two that trigger leaf cell death in Nicotiana benthamiana. In summary, we have revealed new molecular mechanisms involved in the evolution, biotrophy, and pathogenesis of T. horrida.


September 22, 2019  |  

Whole-Genome Analysis of an Extensively Drug-Resistant Acinetobacter baumannii Strain XDR-BJ83: Insights into the Mechanisms of Resistance of an ST368 Strain from a Tertiary Care Hospital in China.

Acinetobacter baumannii is an important pathogen of nosocomial infections. Nosocomial outbreaks caused by antibiotic-resistant A. baumannii remain a significant challenge. Understanding the antibiotic resistance mechanism of A. baumannii is critical for clinical treatment. The purpose of this study was to determine the whole-genome sequence (WGS) of an extensively drug-resistant (XDR) A. baumannii strain, XDR-BJ83, which was associated with a nosocomial outbreak in a tertiary care hospital of China, and to investigate the antibiotic resistance mechanism of this strain. The WGS of XDR-BJ83 was performed using single-molecule real-time sequencing. The complete genome of XDR-BJ83 consisted of a 4,011,552-bp chromosome and a 69,069-bp plasmid. The sequence type of XDR-BJ83 was ST368, which belongs to clonal complex 92 (CC92). The chromosome of XDR-BJ83 carried multiple antibiotic resistance genes, antibiotic efflux pump genes, and mobile genetic elements, including insertion sequences, transposons, integrons, and resistance islands. The plasmid of XDR-BJ83 (pBJ83) was a conjugative plasmid carrying type IV secretion system. These results indicate that the presence of multiple antibiotic resistance genes, efflux pumps, and mobile genetic elements is likely associated with resistance to various antibiotics in XDR-BJ83.


September 22, 2019  |  

Genomic evidence for asymmetric introgression by sexual selection in the common wall lizard.

Strongly selected characters can be transferred from one lineage to another with limited genetic exchange, resulting in asymmetric introgression and a mosaic genome in the receiving population. However, systems are rarely sufficiently well studied to link the pattern of introgression to its underlying process. Male common wall lizards in western Italy exhibit exaggeration of a suite of sexually selected characters that make them outcompete males from a distantly related lineage that lack these characters. This results in asymmetric hybridization and adaptive introgression of the suite of characters following secondary contact. We developed genomewide markers to infer the demographic history of gene flow between different genetic lineages, identify the spread of the sexually selected syndrome, and test the prediction that introgression should be asymmetric and heterogeneous across the genome. Our results show that secondary contact was accompanied by gene flow in both directions across most of the genome, but with approximately 3% of the genome showing highly asymmetric introgression in the predicted direction. Demographic simulations reveal that this asymmetric gene flow is more recent than the initial secondary contact, and the data suggest that the exaggerated male sexual characters originated within the Italian lineage and subsequently spread throughout this lineage before eventually reaching the contact zone. These results demonstrate that sexual selection can cause a suite of characters to spread throughout both closely and distantly related lineages with limited gene flow across the genome at large.© 2018 John Wiley & Sons Ltd.


September 22, 2019  |  

Complete genome sequence of Burkholderia sp. JP2-270, a rhizosphere isolate of rice with antifungal activity against Rhizoctonia solani.

Burkholderia sp. JP2-270, a bacterium with a strong ability to inhibit the growth of Rhizoctonia solani, was isolated from the rhizosphere of rice. The phylogenetic analysis based on 16S rRNA gene revealed that JP2-270 belonged to Burkholderia cepacia complex. Here, we present the complete genome sequence of Burkholderia sp. JP2-270, which consists of three circular chromosomes (Chr1 3,723,585 bp, Chr2 3,274,969 bp, Chr3 1,483,367 bp) and two plasmids (Plas1 15,126 bp, Plas2 428,263 bp). A total of 8193 protein coding genes were predicted in the genome, including 67 tRNA genes, 18 rRNA genes and 4 ncRNA genes. In addition, mutation analysis of Burkholderia sp. JP2-270 revealed that the gene bysR (DM992_17470), encoding a lysR-type transcriptional regulator, was essential for the antagonistic activity of Burkholderia sp. JP2-270 against R. solani GD118 in vitro and in vivo. Identification of regulatory gene associated with antagonistic activity will contribute to understand the antagonistic mechanism of Burkholderia sp. JP2-270. Copyright © 2018 Elsevier Ltd. All rights reserved.


September 22, 2019  |  

Genome mining for fungal polyketide-diterpenoid hybrids: discovery of key terpene cyclases and multifunctional P450s for structural diversification

A biosynthetic gene cluster for chevalone E (1) and its oxidized derivatives have been identified within the genome of the endophytic fungus Aspergillus versicolor 0312, by a mining strategy targeting a polyke- tide-diterpenoid hybrid molecule. The biosynthetic pathway has been successfully reconstituted in the heterologous fungus Aspergillus oryzae. Interestingly, two P450 monooxygenases, Cle2 and Cle4, were found to transform 1 into seven new analogues including 7 and 8 that possess a unique five-membered lactone ring. Furthermore, the replacement of the terpene cyclase gene with that from another fungus led to the production of sartorypyrone D (11), which has a monocyclic terpenoid moiety. Finally, some of the compounds obtained in this study synergistically enhanced the cytotoxicity of doxorubicin (DOX) in breast cancer cells.


September 22, 2019  |  

Comparative genomic analysis revealed rapid differentiation in the pathogenicity-related gene repertoires between Pyricularia oryzae and Pyricularia penniseti isolated from a Pennisetum grass.

A number of Pyricularia species are known to infect different grass species. In the case of Pyricularia oryzae (syn. Magnaporthe oryzae), distinct populations are known to be adapted to a wide variety of grass hosts, including rice, wheat and many other grasses. The genome sizes of Pyricularia species are typical for filamentous ascomycete fungi [~?40 Mbp for P. oryzae, and ~?45 Mbp for P. grisea]. Genome plasticity, mediated in part by deletions promoted by recombination between repetitive elements [Genome Res 26:1091-1100, 2016, Nat Rev Microbiol 10:417-430,2012] and transposable elements [Annu Rev Phytopathol 55:483-503,2017] contributes to host adaptation. Therefore, comparisons of genome structure of individual species will provide insight into the evolution of host specificity. However, except for the P. oryzae subgroup, little is known about the gene content or genome organization of other Pyricularia species, such as those infecting Pennisetum grasses.Here, we report the genome sequence of P. penniseti strain P1609 isolated from a Pennisetum grass (JUJUNCAO) using PacBio SMRT sequencing technology. Phylogenomic analysis of 28 Magnaporthales species and 5 non-Magnaporthales species indicated that P1609 belongs to a Pyricularia subclade, which is genetically distant from P. oryzae. Comparative genomic analysis revealed that the pathogenicity-related gene repertoires had diverged between P1609 and the P. oryzae strain 70-15, including the known avirulence genes, other putative secreted proteins, as well as some other predicted Pathogen-Host Interaction (PHI) genes. Genomic sequence comparison also identified many genomic rearrangements relative to P. oryzae.Our results suggested that the genomic sequence of the P. penniseti P1609 could be a useful resource for the genetic study of the Pennisetum-infecting Pyricularia species and provide new insight into evolution of pathogen genomes during host adaptation.


September 22, 2019  |  

Novel energy conservation strategies and behaviour of Pelotomaculum schinkii driving syntrophic propionate catabolism.

Under methanogenic conditions, short-chain fatty acids are common byproducts from degradation of organic compounds and conversion of these acids is an important component of the global carbon cycle. Due to the thermodynamic difficulty of propionate degradation, this process requires syntrophic interaction between a bacterium and partner methanogen; however, the metabolic strategies and behaviour involved are not fully understood. In this study, the first genome analysis of obligately syntrophic propionate degraders (Pelotomaculum schinkii HH and P. propionicicum MGP) and comparison with other syntrophic propionate degrader genomes elucidated novel components of energy metabolism behind Pelotomaculum propionate oxidation. Combined with transcriptomic examination of P. schinkii behaviour in co-culture with Methanospirillum hungatei, we found that formate may be the preferred electron carrier for P. schinkii syntrophy. Propionate-derived menaquinol may be primarily re-oxidized to formate, and energy was conserved during formate generation through newly proposed proton-pumping formate extrusion. P. schinkii did not overexpress conventional energy metabolism associated with a model syntrophic propionate degrader Syntrophobacter fumaroxidans MPOB (i.e., CoA transferase, Fix and Rnf). We also found that P. schinkii and the partner methanogen may also interact through flagellar contact and amino acid and fructose exchange. These findings provide new understanding of syntrophic energy acquisition and interactions.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.


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