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Asset Tag: Epigenetics

July 7, 2019  |  

Complete genome and methylome sequences of Salmonella enterica subsp. enterica serovar Panama (ATCC 7378) and Salmonella enterica subsp. enterica serovar Sloterdijk (ATCC 15791).

Salmonella enterica spp. are pathogenic bacteria commonly associated with food-borne outbreaks in human and animals. Salmonella enterica spp. are characterized into more than 2,500 different serotypes, which makes epidemiological surveillance and outbreak control more difficult. In this report, we announce the first complete genome and methylome sequences from two Salmonella type strains associated with food-borne outbreaks, Salmonella enterica subsp. enterica serovar Panama (ATCC 7378) and Salmonella enterica subsp. enterica serovar Sloterdijk (ATCC 15791). Copyright © 2016 Yao et al.

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July 7, 2019  |  

Complete genome sequence and methylome of Salmonella enterica subsp. enterica Cerro, a frequent dairy cow serovar.

Salmonella enterica subsp. enterica serovar Cerro is an infrequent pathogen of humans and other mammals but is frequently isolated from the hindgut of asymptomatic cattle in the United States. To further understand the genomic determinants of S. Cerro specificity for the bovine hindgut, the genome of isolate CFSAN001588 was fully sequenced and deposited in the GenBank database. Copyright © 2016 Haley et al.

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July 7, 2019  |  

Complete genome sequence and methylome analysis of Aeromonas hydrophila strain YL17, isolated from a compost pile.

In this report, we announce the complete genome sequence of Aeromonas hydrophila strain YL17. Single-molecule real-time (SMRT) DNA sequencing was used to generate the complete genome sequence and the genome-wide DNA methylation profile of this environmental isolate. A total of five unique DNA methyltransferase recognition motifs were reported here. Copyright © 2016 Lim et al.

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July 7, 2019  |  

Finished genome sequence and methylome of the cyanide-degrading Pseudomonas pseudoalcaligenes strain CECT5344 as resolved by single-molecule real-time sequencing.

Pseudomonas pseudoalcaligenes CECT5344 tolerates cyanide and is also able to utilize cyanide and cyano-derivatives as a nitrogen source under alkaline conditions. The strain is considered as candidate for bioremediation of habitats contaminated with cyanide-containing liquid wastes. Information on the genome sequence of the strain CECT5344 became available previously. The P. pseudoalcaligenes CECT5344 genome was now resequenced by applying the single molecule, real-time (SMRT(®)) sequencing technique developed by Pacific Biosciences. The complete and finished genome sequence of the strain consists of a 4,696,984 bp chromosome featuring a GC-content of 62.34%. Comparative analyses between the new and previous versions of the P. pseudoalcaligenes CECT5344 genome sequence revealed additional regions in the new sequence that were missed in the older version. These additional regions mostly represent mobile genetic elements. Moreover, five additional genes predicted to play a role in sulfoxide reduction are present in the newly established genome sequence. The P. pseudoalcaligenes CECT5344 genome sequence is highly related to the genome sequences of different Pseudomonas mendocina strains. Approximately, 70% of all genes are shared between P. pseudoalcaligenes and P. mendocina. In contrast to P. mendocina, putative pathogenicity genes were not identified in the P. pseudoalcaligenes CECT5344 genome. P. pseudoalcaligenes CECT5344 possesses unique genes for nitrilases and mercury resistance proteins that are of importance for survival in habitats contaminated with cyano- and mercury compounds. As an additional feature of the SMRT sequencing technology, the methylome of P. pseudoalcaligenes was established. Six sequence motifs featuring methylated adenine residues (m6A) were identified in the genome. The genome encodes several methyltransferases, some of which may be considered for methylation of the m6A motifs identified. The complete genome sequence of the strain CECT5344 now provides the basis for exploitation of genetic features for biotechnological purposes. Copyright © 2016 Elsevier B.V. All rights reserved.

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July 7, 2019  |  

Complete nucleotide sequence of pH11, an IncHI2 plasmid conferring multi-antibiotic resistance and multi-heavy metal resistance genes in a clinical Klebsiella pneumoniae isolate.

The complete 284,628bp sequence of pH11, an IncHI2 plasmid, was determined through single-molecule, real-time (SMRT) sequencing. Harbored by a clinical Klebsiella pneumoniae strain H11, and isolated in Beijing, this plasmid contains multiple antibiotic resistance genes, including catA2, aac(6′)-Ib, strB, strA, dfrA19, blaTEM-1, blaSHV-12, sul1, qacE delta 1, ereA, arr2, and aac3. The aac(6′)-Ib is carried by a class I integron. Plasmid pH11 also carries several genes associated with resistance to heavy metals, such as tellurium, mercury, cobalt, zinc, nickel, copper, lead and cadmium. This plasmid exhibits numerous characteristics, including HipBA and RelBE toxin-antitoxin systems, two major transfer (Tra) regions closely related to those of Salmonella enterica serovar plasmid pRH-R27, a type II restriction modification system (EcoRII R-M system), several methyltransferases and methylases and genes encoding Hha and StpA. These characteristics suggest that pH11 may adapt to various hosts and environments. Multiple insertion sequence elements, transposases, recombinases, resolvases and integrases are scattered throughout pH11. The presence of these genes may indicate that horizontal gene transfer occurs frequently in pH11 and thus may facilitate the dissemination of antimicrobial resistance determinants. Our data suggest that pH11 is a chimera gradually assembled through the integration of different horizontally acquired DNA segments via transposition or homologous recombination. Copyright © 2016 Elsevier Inc. All rights reserved.

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July 7, 2019  |  

Regulation of genetic flux between bacteria by restriction-modification systems.

Restriction-modification (R-M) systems are often regarded as bacteria’s innate immune systems, protecting cells from infection by mobile genetic elements (MGEs). Their diversification has been recently associated with the emergence of particularly virulent lineages. However, we have previously found more R-M systems in genomes carrying more MGEs. Furthermore, it has been suggested that R-M systems might favor genetic transfer by producing recombinogenic double-stranded DNA ends. To test whether R-M systems favor or disfavor genetic exchanges, we analyzed their frequency with respect to the inferred events of homologous recombination and horizontal gene transfer within 79 bacterial species. Genetic exchanges were more frequent in bacteria with larger genomes and in those encoding more R-M systems. We created a recognition target motif predictor for Type II R-M systems that identifies genomes encoding systems with similar restriction sites. We found more genetic exchanges between these genomes, independently of their evolutionary distance. Our results reconcile previous studies by showing that R-M systems are more abundant in promiscuous species, wherein they establish preferential paths of genetic exchange within and between lineages with cognate R-M systems. Because the repertoire and/or specificity of R-M systems in bacterial lineages vary quickly, the preferential fluxes of genetic transfer within species are expected to constantly change, producing time-dependent networks of gene transfer.

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July 7, 2019  |  

Structure of Type IIL restriction-modification enzyme MmeI in complex with DNA has implications for engineering new specificities.

The creation of restriction enzymes with programmable DNA-binding and -cleavage specificities has long been a goal of modern biology. The recently discovered Type IIL MmeI family of restriction-and-modification (RM) enzymes that possess a shared target recognition domain provides a framework for engineering such new specificities. However, a lack of structural information on Type IIL enzymes has limited the repertoire that can be rationally engineered. We report here a crystal structure of MmeI in complex with its DNA substrate and an S-adenosylmethionine analog (Sinefungin). The structure uncovers for the first time the interactions that underlie MmeI-DNA recognition and methylation (5′-TCCRAC-3′; R = purine) and provides a molecular basis for changing specificity at four of the six base pairs of the recognition sequence (5′-TCCRAC-3′). Surprisingly, the enzyme is resilient to specificity changes at the first position of the recognition sequence (5′-TCCRAC-3′). Collectively, the structure provides a basis for engineering further derivatives of MmeI and delineates which base pairs of the recognition sequence are more amenable to alterations than others.

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July 7, 2019  |  

A hot L1 retrotransposon evades somatic repression and initiates human colorectal cancer.

Although human LINE-1 (L1) elements are actively mobilized in many cancers, a role for somatic L1 retrotransposition in tumor initiation has not been conclusively demonstrated. Here, we identify a novel somatic L1 insertion in the APC tumor suppressor gene that provided us with a unique opportunity to determine whether such insertions can actually initiate colorectal cancer (CRC), and if so, how this might occur. Our data support a model whereby a hot L1 source element on Chromosome 17 of the patient’s genome evaded somatic repression in normal colon tissues and thereby initiated CRC by mutating the APC gene. This insertion worked together with a point mutation in the second APC allele to initiate tumorigenesis through the classic two-hit CRC pathway. We also show that L1 source profiles vary considerably depending on the ancestry of an individual, and that population-specific hot L1 elements represent a novel form of cancer risk. © 2016 Scott et al.; Published by Cold Spring Harbor Laboratory Press.

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July 7, 2019  |  

A roadmap for gene system development in Clostridium.

Clostridium species are both heroes and villains. Some cause serious human and animal diseases, those present in the gut microbiota generally contribute to health and wellbeing, while others represent useful industrial chassis for the production of chemicals and fuels. To understand, counter or exploit, there is a fundamental requirement for effective systems that may be used for directed or random genome modifications. We have formulated a simple roadmap whereby the necessary gene systems maybe developed and deployed. At its heart is the use of ‘pseudo-suicide’ vectors and the creation of a pyrE mutant (a uracil auxotroph), initially aided by ClosTron technology, but ultimately made using a special form of allelic exchange termed ACE (Allele-Coupled Exchange). All mutants, regardless of the mutagen employed, are made in this host. This is because through the use of ACE vectors, mutants can be rapidly complemented concomitant with correction of the pyrE allele and restoration of uracil prototrophy. This avoids the phenotypic effects frequently observed with high copy number plasmids and dispenses with the need to add antibiotic to ensure plasmid retention. Once available, the pyrE host may be used to stably insert all manner of application specific modules. Examples include, a sigma factor to allow deployment of a mariner transposon, hydrolases involved in biomass deconstruction and therapeutic genes in cancer delivery vehicles. To date, provided DNA transfer is obtained, we have not encountered any clostridial species where this technology cannot be applied. These include, Clostridium difficile, Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium botulinum, Clostridium perfringens, Clostridium sporogenes, Clostridium pasteurianum, Clostridium ljungdahlii, Clostridium autoethanogenum and even Geobacillus thermoglucosidasius. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

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July 7, 2019  |  

Expression and purification of the modification-dependent restriction enzyme BisI and its homologous enzymes.

The methylation-dependent restriction endonuclease (REase) BisI (G(m5)C???NGC) is found in Bacillus subtilis T30. We expressed and purified the BisI endonuclease and 34 BisI homologs identified in bacterial genomes. 23 of these BisI homologs are active based on digestion of (m5)C-modified substrates. Two major specificities were found among these BisI family enzymes: Group I enzymes cut GCNGC containing two to four (m5)C in the two strands, or hemi-methylated sites containing two (m5)C in one strand; Group II enzymes only cut GCNGC sites containing three to four (m5)C, while one enzyme requires all four cytosines to be modified for cleavage. Another homolog, Esp638I cleaves GCS???SGC (relaxed specificity RCN???NGY, containing at least four (m5)C). Two BisI homologs show degenerate specificity cleaving unmodified DNA. Many homologs are small proteins ranging from 150 to 190 amino acid (aa) residues, but some homologs associated with mobile genetic elements are larger and contain an extra C-terminal domain. More than 156 BisI homologs are found in >60 bacterial genera, indicating that these enzymes are widespread in bacteria. They may play an important biological function in restricting pre-modified phage DNA.

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July 7, 2019  |  

Complete genome sequence of highly virulent Haemophilus parasuis serotype 11 strain SC1401.

Haemophilus parasuis, a normal Gram-negative bacterium, may cause Glässer’s disease and pneumonia in pigs. This study aims to identify the genes related to natural competence of the serotype 11 strain SC1401, which frequently shows competence and high pathogenicity. SC1401 shows many differences from strains without natural competence within the molecular basis. We performed complete genome sequencing together with restriction modification system analysis to lay the foundation for later study. Copyright © 2016 Dai et al.

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July 7, 2019  |  

Recombination rate heterogeneity within Arabidopsis disease resistance genes.

Meiotic crossover frequency varies extensively along chromosomes and is typically concentrated in hotspots. As recombination increases genetic diversity, hotspots are predicted to occur at immunity genes, where variation may be beneficial. A major component of plant immunity is recognition of pathogen Avirulence (Avr) effectors by resistance (R) genes that encode NBS-LRR domain proteins. Therefore, we sought to test whether NBS-LRR genes would overlap with meiotic crossover hotspots using experimental genetics in Arabidopsis thaliana. NBS-LRR genes tend to physically cluster in plant genomes; for example, in Arabidopsis most are located in large clusters on the south arms of chromosomes 1 and 5. We experimentally mapped 1,439 crossovers within these clusters and observed NBS-LRR gene associated hotspots, which were also detected as historical hotspots via analysis of linkage disequilibrium. However, we also observed NBS-LRR gene coldspots, which in some cases correlate with structural heterozygosity. To study recombination at the fine-scale we used high-throughput sequencing to analyze ~1,000 crossovers within the RESISTANCE TO ALBUGO CANDIDA1 (RAC1) R gene hotspot. This revealed elevated intragenic crossovers, overlapping nucleosome-occupied exons that encode the TIR, NBS and LRR domains. The highest RAC1 recombination frequency was promoter-proximal and overlapped CTT-repeat DNA sequence motifs, which have previously been associated with plant crossover hotspots. Additionally, we show a significant influence of natural genetic variation on NBS-LRR cluster recombination rates, using crosses between Arabidopsis ecotypes. In conclusion, we show that a subset of NBS-LRR genes are strong hotspots, whereas others are coldspots. This reveals a complex recombination landscape in Arabidopsis NBS-LRR genes, which we propose results from varying coevolutionary pressures exerted by host-pathogen relationships, and is influenced by structural heterozygosity.

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July 7, 2019  |  

Bacterial genetics: SMRT-seq reveals an epigenetic switch.

Streptococcus pneumoniae uses genetic diversification as a strategy to achieve phenotypic plasticity. For example, DNA inversion of the hsdS genes of type I restriction-modification (R-M) systems determines whether S. pneumoniae forms opaque or transparent colonies, which have different colonization and virulence characteristics. Zhang and colleagues now use single-molecule, real-time sequencing (SMRT-seq) to show the allelic variation of hsdS that results from site-specific recombination forms part of an epigenetic switch.

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