April 21, 2020  |  

Plasmid-encoded tet(X) genes that confer high-level tigecycline resistance in Escherichia coli.

Tigecycline is one of the last-resort antibiotics to treat complicated infections caused by both multidrug-resistant Gram-negative and Gram-positive bacteria1. Tigecycline resistance has sporadically occurred in recent years, primarily due to chromosome-encoding mechanisms, such as overexpression of efflux pumps and ribosome protection2,3. Here, we report the emergence of the plasmid-mediated mobile tigecycline resistance mechanism Tet(X4) in Escherichia coli isolates from China, which is capable of degrading all tetracyclines, including tigecycline and the US FDA newly approved eravacycline. The tet(X4)-harbouring IncQ1 plasmid is highly transferable, and can be successfully mobilized and stabilized in recipient clinical and laboratory strains of Enterobacteriaceae bacteria. It is noteworthy that tet(X4)-positive E.?coli strains, including isolates co-harbouring mcr-1, have been widely detected in pigs, chickens, soil and dust samples in China. In vivo murine models demonstrated that the presence of Tet(X4) led to tigecycline treatment failure. Consequently, the emergence of plasmid-mediated Tet(X4) challenges the clinical efficacy of the entire family of tetracycline antibiotics. Importantly, our study raises concern that the plasmid-mediated tigecycline resistance may further spread into various ecological niches and into clinical high-risk pathogens. Collective efforts are in urgent need to preserve the potency of these essential antibiotics.

April 21, 2020  |  

The complete chloroplast genome sequence of watercress (Nasturtium officinale R. Br.): Genome organization, adaptive evolution and phylogenetic relationships in Cardamineae.

Watercress (Nasturtium officinale R. Br.), an aquatic leafy vegetable of the Brassicaceae family, is known as a nutritional powerhouse. Here, we de novo sequenced and assembled the complete chloroplast (cp) genome of watercress based on combined PacBio and Illumina data. The cp genome is 155,106?bp in length, exhibiting a typical quadripartite structure including a pair of inverted repeats (IRA and IRB) of 26,505?bp separated by a large single copy (LSC) region of 84,265?bp and a small single copy (SSC) region of 17,831?bp. The genome contained 113 unique genes, including 79 protein-coding genes, 30 tRNAs and 4 rRNAs, with 20 duplicate in the IRs. Compared with the prior cp genome of watercress deposited in GenBank, 21 single nucleotide polymorphisms (SNPs) and 27 indels were identified, mainly located in noncoding sequences. A total of 49 repeat structures and 71 simple sequence repeats (SSRs) were detected. Codon usage showed a bias for A/T-ending codons in the cp genome of watercress. Moreover, 45 RNA editing sites were predicted in 16 genes, all for C-to-U transitions. A comparative plastome study with Cardamineae species revealed a conserved gene order and high similarity of protein-coding sequences. Analysis of the Ka/Ks ratios of Cardamineae suggested positive selection exerted on the ycf2 gene in watercress, which might reflect specific adaptations of watercress to its particular living environment. Phylogenetic analyses based on complete cp genomes and common protein-coding genes from 56 species showed that the genus Nasturtium was a sister to Cardamine in the Cardamineae tribe. Our study provides valuable resources for future evolution, population genetics and molecular biology studies of watercress. Copyright © 2019 Elsevier B.V. All rights reserved.

September 22, 2019  |  

The genome of an underwater architect, the caddisfly Stenopsyche tienmushanensis Hwang (Insecta: Trichoptera).

Caddisflies (Insecta: Trichoptera) are a highly adapted freshwater group of insects split from a common ancestor with Lepidoptera. They are the most diverse (>16,000 species) of the strictly aquatic insect orders and are widely employed as bio-indicators in water quality assessment and monitoring. Among the numerous adaptations to aquatic habitats, caddisfly larvae use silk and materials from the environment (e.g., stones, sticks, leaf matter) to build composite structures such as fixed retreats and portable cases. Understanding how caddisflies have adapted to aquatic habitats will help explain the evolution and subsequent diversification of the group.We sequenced a retreat-builder caddisfly Stenopsyche tienmushanensis Hwang and assembled a high-quality genome from both Illumina and Pacific Biosciences (PacBio) sequencing. In total, 601.2 M Illumina reads (90.2 Gb) and 16.9 M PacBio subreads (89.0 Gb) were generated. The 451.5 Mb assembled genome has a contig N50 of 1.29 M, has a longest contig of 4.76 Mb, and covers 97.65% of the 1,658 insect single-copy genes as assessed by Benchmarking Universal Single-Copy Orthologs. The genome comprises 36.76% repetitive elements. A total of 14,672 predicted protein-coding genes were identified. The genome revealed gene expansions in specific groups of the cytochrome P450 family and olfactory binding proteins, suggesting potential genomic features associated with pollutant tolerance and mate finding. In addition, the complete gene complex of the highly repetitive H-fibroin, the major protein component of caddisfly larval silk, was assembled.We report the draft genome of Stenopsyche tienmushanensis, the highest-quality caddisfly genome so far. The genome information will be an important resource for the study of caddisflies and may shed light on the evolution of aquatic insects.

September 22, 2019  |  

Improved high-quality genome assembly and annotation of Tibetan hulless barley

Background The Tibetan hulless barley (Hordeum vulgare L. var. nudum), also called textquotedblleftQingketextquotedblright in Chinese and textquotedblleftNetextquotedblright in Tibetan, is the staple food for Tibetans and an important livestock feed in the Tibetan Plateau. The Tibetan hulless barley in China has about 3500 years of cultivation history, mainly produced in Tibet, Qinghai, Sichuan, Yunnan and other areas. In addition, Tibetan hulless barley has rich nutritional value and outstanding health effects, including the beta glucan, dietary fiber, amylopectin, the contents of trace elements, which are higher than any other cereal crops.Findings Here, we reported an improved high-quality assembly of Tibetan hulless barley genome with 4.0 Gb in size. We employed the falcon assembly package, scaffolding and error correction tools to finish improvement using PacBio long reads sequencing technology, with contig and scaffold N50 lengths of 1.563Mb and 4.006Mb, respectively, representing more continuous than the original Tibetan hulless barley genome nearly two orders of magnitude. We also re-annotated the new assembly, and reported 61,303 stringent confident putative protein-coding genes, of which 40,457 is HC genes. We have developed a new Tibetan hulless barley genome database (THBGD) to download and use friendly, as well as to better manage the information of the Tibetan hulless barley genetic resources.Conclusions The availability of new Tibetan hulless barley genome and annotations will take the genetics of Tibetan hulless barley to a new level and will greatly simplify the breeders effort. It will also enrich the granary of the Tibetan people.AbbreviationsBLASTBasic Local Alignment Search ToolBUSCOBenchmarking Universal Single-Copy OrthologsQVquality valuePacBioPacifc BiosciencesRNA-seqRNA sequencingNGSNext generation sequencingTGSThird generation sequencingTHBGDTibetan hulless barley Genome Database

July 19, 2019  |  

Long-read sequence assembly of the firefly Pyrocoelia pectoralis genome.

Fireflies are a family of insects within the beetle order Coleoptera, or winged beetles, and they are one of the most well-known and loved insect species because of their bioluminescence. However, the firefly is in danger of extinction because of the massive destruction of its living environment. In order to improve the understanding of fireflies and protect them effectively, we sequenced the whole genome of the terrestrial firefly Pyrocoelia pectoralis.Here, we developed a highly reliable genome resource for the terrestrial firefly Pyrocoelia pectoralis (E. Oliv., 1883; Coleoptera: Lampyridae) using single molecule real time (SMRT) sequencing on the PacBio Sequel platform. In total, 57.8 Gb of long reads were generated and assembled into a 760.4-Mb genome, which is close to the estimated genome size and covered 98.7% complete and 0.7% partial insect Benchmarking Universal Single-Copy Orthologs. The k-mer analysis showed that this genome is highly heterozygous. However, our long-read assembly demonstrates continuousness with a contig N50 length of 3.04 Mb and the longest contig length of 13.69 Mb. Furthermore, 135 589 SSRs and 341 Mb of repeat sequences were detected. A total of 23 092 genes were predicted; 88.44% of genes were annotated with one or more related functions.We assembled a high-quality firefly genome, which will not only provide insights into the conservation and biodiversity of fireflies, but also provide a wealth of information to study the mechanisms of their sexual communication, bio-luminescence, and evolution.© The Authors 2017. Published by Oxford University Press.

July 7, 2019  |  

The complete chloroplast genome sequence of tung tree (Vernicia fordii): Organization and phylogenetic relationships with other angiosperms.

Tung tree (Vernicia fordii) is an economically important tree widely cultivated for industrial oil production in China. To better understand the molecular basis of tung tree chloroplasts, we sequenced and characterized its genome using PacBio RS II sequencing platforms. The chloroplast genome was sequenced with 161,528?bp in length, composed with one pair of inverted repeats (IRs) of 26,819?bp, which were separated by one small single copy (SSC; 18,758?bp) and one large single copy (LSC; 89,132?bp). The genome contains 114 genes, coding for 81 protein, four ribosomal RNAs and 29 transfer RNAs. An expansion with integration of an additional rps19 gene in the IR regions was identified. Compared to the chloroplast genome of Jatropha curcas, a species from the same family, the tung tree chloroplast genome is distinct with 85 single nucleotide polymorphisms (SNPs) and 82 indels. Phylogenetic analysis suggests that V. fordii is a sister species with J. curcas within the Eurosids I. The nucleotide sequence provides vital molecular information for understanding the biology of this important oil tree.

July 7, 2019  |  

Isolation and complete genome sequence of Halorientalis hydrocarbonoclasticus sp. nov., a hydrocarbon-degrading haloarchaeon.

Bioremediation in hypersaline environments is particularly challenging since the microbes that tolerate such harsh environments and degrade pollutants are quite scarce. Haloarchaea, however, due to their inherent ability to grow at high salt concentrations, hold great promise for remediating the contaminated hypersaline sites. This study aimed to isolate and characterize novel haloarchaeal strains with potentials in hydrocarbon degradation. A haloarchaeal strain IM1011 was isolated from Changlu Tanggu saltern near Da Gang Oilfield in Tianjin (China) by enrichment culture in hypersaline medium containing hexadecane. It could degrade 57 ± 5.2% hexadecane (5 g/L) in the presence of 3.6 M NaCl at 37 °C within 24 days. To get further insights into the mechanisms of petroleum hydrocarbon degradation in haloarchaea, complete genome (3,778,989 bp) of IM1011 was sequenced. Phylogenetic analysis of 16S rRNA gene, RNA polymerase beta-subunit (rpoB’) gene and of the complete genome suggested IM1011 to be a new species in Halorientalis genus, and the name Halorientalis hydrocarbonoclasticus sp. nov., is proposed. Notably, with insights from the IM1011 genome sequence, the involvement of diverse alkane hydroxylase enzymes and an intact ß-oxidation pathway in hexadecane biodegradation was predicted. This is the first hexadecane-degrading strain from Halorientalis genus, of which the genome sequence information would be helpful for further dissecting the hydrocarbon degradation by haloarchaea and for their application in bioremediation of oil-polluted hypersaline environments.

July 7, 2019  |  

Complete chloroplast genome sequences of Eucommia ulmoides: genome structure and evolution.

Eucommia ulmoides is an important traditional medicinal plant that is used for the production of locative Eucommia rubber. In this study, the complete chloroplast (cp) genome sequence of E. ulmoides was obtained by total DNA sequencing; this is the first cp genome sequence of the order Garryales. The cp genome of E. ulmoides was 163,341 bp long and included a pair of inverted repeat (IR) regions (31,300 bp), one large single copy (LSC) region (86,592 bp), and one small single copy (SSC) region (14,149 bp). The genome structure and GC content were similar to those of typical angiosperm cp genomes and contained 115 unique genes, including 80 protein-coding genes, 31 transfer RNA (tRNAs), and four ribosomal RNA (rRNAs). Compared with the entire cp genome sequence, three unique genome rearrangements were observed in the LSC region. Moreover, compared with the Sesamum and Nicotiana cp genomes, E. ulmoides contained no indels in the IR regions, and variable regions were identified in noncoding regions. The E. ulmoides cp genome showed extreme expansion at the IR/SSC boundary owing to the integration of an additional complete gene, ycf1. Twenty-nine simple sequence repeats (SSRs) were identified in the E. ulmoides cp genome. In addition, 36 protein-coding genes were used for phylogenetic inference, supporting a sister relationship between E. ulmoides and Aucuba, which belongs to Euasterids I. In summary, we described the complete cp genome sequence of E. ulmoides; this information will be useful for phylogenetic and evolutionary studies.

July 7, 2019  |  

Complete genome sequence of the Streptomyces sp. strain CdTB01, a bacterium tolerant to cadmium.

Streptomyces sp. Strain CdTB01, which is tolerant to high concentrations of heavy metals, particularly cadmium, was isolated from soil contaminated with heavy metals. Two contigs with total genome size of 10.19Mb were identified in the whole genome sequencing and assembly, and numerous homologous genes known to be involved in heavy metal resistance were found in the genome. Copyright © 2016 Elsevier B.V. All rights reserved.

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