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July 7, 2019

Finished genome sequences of Xanthomonas fragariae, the cause of bacterial angular leaf spot of strawberry.

Xanthomonas fragariae is a foliar pathogen of strawberry that is of significant concern to nursery production of strawberry transplants and field production of strawberry fruit. Long-read sequencing was employed to generate finished genomes for two isolates (each with one chromosome and two plasmids) from symptomatic plants in northern California. Copyright © 2016 Henry and Leveau.


July 7, 2019

Pathogenesis of multi drug-resistant and extensively drug-resistant tuberculosis as a determinant of future treatment success.

Multidrug-resistant (MDR)/extensively drug-resistant (XDR) tuberculosis (TB) is a significant threat to global TB control [1]. In most cases, treatment of MDR/XDR TB is not standardized, and clinicians have adopted a variety of treatment strategies. These strategies include switching to a regimen of new drugs, increasing the dosage of the same drugs, rarely used drugs (which have widespread resistance), etc. Drug resistance is a manmade phenomenon that is driven by treatment strategy (i.e., regimen). These divergent approaches may differentially drive the evolution of bacteria. Some instances of this evolution have already occurred [2]. The community’s focus has been on drug resistance; therefore, the consequence of this divergence is usually by different mechanisms of resistance [2] and [3]. However, the full scope of the consequential microevolution frequently goes unnoticed because it also affects important factors such as fitness and virulence. In this study, we aimed to develop a comprehensive understanding of the consequences of differential TB treatment to build more accurate prognostics for future treatments.


July 7, 2019

Deciphering the virulence factors of the opportunistic pathogen Mycobacterium colombiense.

Mycobacterium avium complex (MAC) contains clinically important nontuberculous mycobacteria worldwide and is the second largest medical complex in the Mycobacterium genus after the Mycobacterium tuberculosis complex. MAC comprises several species that are closely phylogenetically related but diverse regarding their host preference, course of disease, virulence and immune response. In this study we provided immunologic and virulence-related insights into the M. colombiense genome as a model of an opportunistic pathogen in the MAC. By using bioinformatic tools we found that M. colombiense has deletions in the genes involved in p-HBA/PDIM/PGL, PLC, SL-1 and HspX production, and loss of the ESX-1 locus. This information not only sheds light on our understanding the virulence mechanisms used by opportunistic MAC pathogens but also has great potential for the designing of species-specific diagnostic tools.


July 7, 2019

A complete toolset for the study of Ustilago bromivora and Brachypodium sp. as a fungal-temperate grass pathosystem.

Due to their economic relevance, the study of plant pathogen interactions is of importance. However, elucidating these interactions and their underlying molecular mechanisms remains challenging since both host and pathogen need to be fully genetically accessible organisms. Here we present milestones in the establishment of a new biotrophic model pathosystem: Ustilago bromivora and Brachypodium sp. We provide a complete toolset, including an annotated fungal genome and methods for genetic manipulation of the fungus and its host plant. This toolset will enable researchers to easily study biotrophic interactions at the molecular level on both the pathogen and the host side. Moreover, our research on the fungal life cycle revealed a mating type bias phenomenon. U. bromivora harbors a haplo-lethal allele that is linked to one mating type region. As a result, the identified mating type bias strongly promotes inbreeding, which we consider to be a potential speciation driver.


July 7, 2019

Genomic analysis of phylotype I strain EP1 reveals substantial divergence from other strains in the Ralstonia solanacearum species complex.

Ralstonia solanacearum species complex is a devastating group of phytopathogens with an unusually wide host range and broad geographical distribution. R. solanacearum isolates may differ considerably in various properties including host range and pathogenicity, but the underlying genetic bases remain vague. Here, we conducted the genome sequencing of strain EP1 isolated from Guangdong Province of China, which belongs to phylotype I and is highly virulent to a range of solanaceous crops. Its complete genome contains a 3.95-Mb chromosome and a 2.05-Mb mega-plasmid, which is considerably bigger than reported genomes of other R. solanacearum strains. Both the chromosome and the mega-plasmid have essential house-keeping genes and many virulence genes. Comparative analysis of strain EP1 with other 3 phylotype I and 3 phylotype II, III, IV strains unveiled substantial genome rearrangements, insertions and deletions. Genome sequences are relatively conserved among the 4 phylotype I strains, but more divergent among strains of different phylotypes. Moreover, the strains exhibited considerable variations in their key virulence genes, including those encoding secretion systems and type III effectors. Our results provide valuable information for further elucidation of the genetic basis of diversified virulences and host range of R. solanacearum species.


July 7, 2019

Complete genome sequence of Clostridium estertheticum DSM 8809, a microbe identified in spoiled vacuum packed beef.

Blown pack spoilage (BPS) is a major issue for the beef industry. Etiological agents of BPS involve members of a group of Clostridium species, including Clostridium estertheticum which has the ability to produce gas, mostly carbon dioxide, under anaerobic psychotrophic growth conditions. This spore-forming bacterium grows slowly under laboratory conditions, and it can take up to 3 months to produce a workable culture. These characteristics have limited the study of this commercially challenging bacterium. Consequently information on this bacterium is limited and no effective controls are currently available to confidently detect and manage this production risk. In this study the complete genome of C. estertheticum DSM 8809 was determined by SMRT(®) sequencing. The genome consists of a circular chromosome of 4.7 Mbp along with a single plasmid carrying a potential tellurite resistance gene tehB and a Tn3-like resolvase-encoding gene tnpR. The genome sequence was searched for central metabolic pathways that would support its biochemical profile and several enzymes contributing to this phenotype were identified. Several putative antibiotic/biocide/metal resistance-encoding genes and virulence factors were also identified in the genome, a feature that requires further research. The availability of the genome sequence will provide a basic blueprint from which to develop valuable biomarkers that could support and improve the detection and control of this bacterium along the beef production chain.


July 7, 2019

Complete sequence of a F33:A-:B- conjugative plasmid carrying the oqxAB, fosA3, and blaCTX-M-55 elements from a foodborne Escherichia coli strain.

This study reports the complete sequence of pE80, a conjugative IncFII plasmid recovered from an Escherichia coli strain isolated from chicken meat. This plasmid harbors multiple resistance determinants including oqxAB, fosA3, blaCTX-M-55, and blaTEM-1, and is a close variant of the recently reported p42-2 element, which was recovered from E. coli of veterinary source. Recovery of pE80 constitutes evidence that evolution or genetic re-arrangement of IncFII type plasmids residing in animal-borne organisms is an active event, which involves acquisition and integration of foreign resistance elements into the plasmid backbone. Dissemination of these plasmids may further compromise the effectiveness of current antimicrobial strategies.


July 7, 2019

The genome of the toluene-degrading Pseudomonas veronii strain 1YdBTEX2 and its differential gene expression in contaminated sand.

The natural restoration of soils polluted by aromatic hydrocarbons such as benzene, toluene, ethylbenzene and m- and p-xylene (BTEX) may be accelerated by inoculation of specific biodegraders (bioaugmentation). Bioaugmentation mainly involves introducing bacteria that deploy their metabolic properties and adaptation potential to survive and propagate in the contaminated environment by degrading the pollutant. In order to better understand the adaptive response of cells during a transition to contaminated material, we analyzed here the genome and short-term (1 h) changes in genome-wide gene expression of the BTEX-degrading bacterium Pseudomonas veronii 1YdBTEX2 in non-sterile soil and liquid medium, both in presence or absence of toluene. We obtained a gapless genome sequence of P. veronii 1YdBTEX2 covering three individual replicons with a total size of 8 Mb, two of which are largely unrelated to current known bacterial replicons. One-hour exposure to toluene, both in soil and liquid, triggered massive transcription (up to 208-fold induction) of multiple gene clusters, such as toluene degradation pathway(s), chemotaxis and toluene efflux pumps. This clearly underlines their key role in the adaptive response to toluene. In comparison to liquid medium, cells in soil drastically changed expression of genes involved in membrane functioning (e.g., lipid composition, lipid metabolism, cell fatty acid synthesis), osmotic stress response (e.g., polyamine or trehalose synthesis, uptake of potassium) and putrescine metabolism, highlighting the immediate response mechanisms of P. veronii 1YdBTEX2 for successful establishment in polluted soil.


July 7, 2019

Whole-genome de novo sequencing, combined with RNA-Seq analysis, reveals unique genome and physiological features of the amylolytic yeast Saccharomycopsis fibuligera and its interspecies hybrid.

Genomic studies on fungal species with hydrolytic activity have gained increased attention due to their great biotechnological potential for biomass-based biofuel production. The amylolytic yeast Saccharomycopsis fibuligera has served as a good source of enzymes and genes involved in saccharification. Despite its long history of use in food fermentation and bioethanol production, very little is known about the basic physiology and genomic features of S. fibuligera.We performed whole-genome (WG) de novo sequencing and complete assembly of S. fibuligera KJJ81 and KPH12, two isolates from wheat-based Nuruk in Korea. Intriguingly, the KJJ81 genome (~38 Mb) was revealed as a hybrid between the KPH12 genome (~18 Mb) and another unidentified genome sharing 88.1% nucleotide identity with the KPH12 genome. The seven chromosome pairs of KJJ81 subgenomes exhibit highly conserved synteny, indicating a very recent hybridization event. The phylogeny inferred from WG comparisons showed an early divergence of S. fibuligera before the separation of the CTG and Saccharomycetaceae clades in the subphylum Saccharomycotina. Reconstructed carbon and sulfur metabolic pathways, coupled with RNA-Seq analysis, suggested a marginal Crabtree effect under high glucose and activation of sulfur metabolism toward methionine biosynthesis under sulfur limitation in this yeast. Notably, the lack of sulfate assimilation genes in the S. fibuligera genome reflects a unique phenotype for Saccharomycopsis clades as natural sulfur auxotrophs. Extended gene families, including novel genes involved in saccharification and proteolysis, were identified. Moreover, comparative genome analysis of S. fibuligera ATCC 36309, an isolate from chalky rye bread in Germany, revealed that an interchromosomal translocation occurred in the KPH12 genome before the generation of the KJJ81 hybrid genome.The completely sequenced S. fibuligera genome with high-quality annotation and RNA-Seq analysis establishes an important foundation for functional inference of S. fibuligera in the degradation of fermentation mash. The gene inventory facilitates the discovery of new genes applicable to the production of novel valuable enzymes and chemicals. Moreover, as the first gapless genome assembly in the genus Saccharomycopsis including members with desirable traits for bioconversion, the unique genomic features of S. fibuligera and its hybrid will provide in-depth insights into fungal genome dynamics as evolutionary adaptation.


July 7, 2019

Active and adaptive Legionella CRISPR-Cas reveals a recurrent challenge to the pathogen.

Clustered regularly interspaced short palindromic repeats with CRISPR-associated gene (CRISPR-Cas) systems are widely recognized as critical genome defense systems that protect microbes from external threats such as bacteriophage infection. Several isolates of the intracellular pathogen Legionella pneumophila possess multiple CRISPR-Cas systems (type I-C, type I-F and type II-B), yet the targets of these systems remain unknown. With the recent observation that at least one of these systems (II-B) plays a non-canonical role in supporting intracellular replication, the possibility remained that these systems are vestigial genome defense systems co-opted for other purposes. Our data indicate that this is not the case. Using an established plasmid transformation assay, we demonstrate that type I-C, I-F and II-B CRISPR-Cas provide protection against spacer targets. We observe efficient laboratory acquisition of new spacers under ‘priming’ conditions, in which initially incomplete target elimination leads to the generation of new spacers and ultimate loss of the invasive DNA. Critically, we identify the first known target of L. pneumophila CRISPR-Cas: a 30?kb episome of unknown function whose interbacterial transfer is guarded against by CRISPR-Cas. We provide evidence that the element can subvert CRISPR-Cas by mutating its targeted sequences – but that primed spacer acquisition may limit this mechanism of escape. Rather than generally impinging on bacterial fitness, this element drives a host specialization event – with improved fitness in Acanthamoeba but a reduced ability to replicate in other hosts and conditions. These observations add to a growing body of evidence that host range restriction can serve as an existential threat to L. pneumophila in the wild.© 2016 The Authors Cellular Microbiology Published by John Wiley & Sons Ltd.


July 7, 2019

Genome sequence of Prosthecochloris sp. strain CIB 2401 of the phylum Chlorobi.

To date, only 13 genomes of green sulfur bacteria (family Chlorobiaceae) have been sequenced. The sequenced strains do not cover the full phylogenetic diversity of the family. We determined the complete genome sequence of Prosthecochloris sp. strain CIB 2401, thereby increasing the genome information for the poorly represented marine Chlorobiaceae. Copyright © 2016 Nabhan et al.


July 7, 2019

Chromosome assembly of large and complex genomes using multiple references

Despite the rapid development of sequencing technologies, assembly of mammalian-scale genomes into complete chromosomes remains one of the most challenging problems in bioinformatics. To help address this difficulty, we developed Ragout, a reference-assisted assembly tool that now works for large and complex genomes. Taking one or more target assemblies (generated from an NGS assembler) and one or multiple related reference genomes, Ragout infers the evolutionary relationships between the genomes and builds the final assemblies using a genome rearrangement approach. Using Ragout, we transformed NGS assemblies of 15 different Mus musculus and one Mus spretus genomes into sets of complete chromosomes, leaving less than 5% of sequence unlocalized per set. Various benchmarks, including PCR testing and realigning of long PacBio reads, suggest only a small number of structural errors in the final assemblies, comparable with direct assembly approaches. Additionally, we applied Ragout to Mus caroli and Mus pahari genomes, which exhibit karyotype-scale variations compared to other genomes from the Muridae family. Chromosome color maps confirmed most large-scale rearrangements that Ragout detected.


July 7, 2019

Complete genome sequences of six Legionella pneumophila isolates from two collocated outbreaks of Legionnaires’ disease in 2005 and 2008 in Sarpsborg/Fredrikstad, Norway.

Here, we report the complete genome sequences of Legionella pneumophila isolates from two collocated outbreaks of Legionnaires’ disease in 2005 and 2008 in Sarpsborg/Fredrikstad, Norway. One clinical and two environmental isolates were sequenced from each outbreak. The genome of all six isolates consisted of a 3.36 Mb-chromosome, while the 2005 genomes featured an additional 68 kb-episome sharing high sequence similarity with the L. pneumophila Lens plasmid. All six genomes contained multiple mobile genetic elements including novel combinations of type-IVA secretion systems. A comparative genomics study will be launched to resolve the genetic relationship between the L. pneumophila isolates. Copyright © 2016 Dybwad et al.


July 7, 2019

Listeria monocytogenes in stone fruits linked to a multistate outbreak: enumeration of cells and whole-genome sequencing.

In 2014, the identification of stone fruits contaminated with Listeria monocytogenes led to the subsequent identification of a multistate outbreak. Simultaneous detection and enumeration of L. monocytogenes were performed on 105 fruits, each weighing 127 to 145 g, collected from 7 contaminated lots. The results showed that 53.3% of the fruits yielded L. monocytogenes (lower limit of detection, 5 CFU/fruit), and the levels ranged from 5 to 2,850 CFU/fruit, with a geometric mean of 11.3 CFU/fruit (0.1 CFU/g of fruit). Two serotypes, IVb-v1 and 1/2b, were identified by a combination of PCR- and antiserum-based serotyping among isolates from fruits and their packing environment; certain fruits contained a mixture of both serotypes. Single nucleotide polymorphism (SNP)-based whole-genome sequencing (WGS) analysis clustered isolates from two case-patients with the serotype IVb-v1 isolates and distinguished outbreak-associated isolates from pulsed-field gel electrophoresis (PFGE)-matched, but epidemiologically unrelated, clinical isolates. The outbreak-associated isolates differed by up to 42 SNPs. All but one serotype 1/2b isolate formed another WGS cluster and differed by up to 17 SNPs. Fully closed genomes of isolates from the stone fruits were used as references to maximize the resolution and to increase our confidence in prophage analysis. Putative prophages were conserved among isolates of each WGS cluster. All serotype IVb-v1 isolates belonged to singleton sequence type 382 (ST382); all but one serotype 1/2b isolate belonged to clonal complex 5.WGS proved to be an excellent tool to assist in the epidemiologic investigation of listeriosis outbreaks. The comparison at the genome level contributed to our understanding of the genetic diversity and variations among isolates involved in an outbreak or isolates associated with food and environmental samples from one facility. Fully closed genomes increased our confidence in the identification and comparison of accessory genomes. The diversity among the outbreak-associated isolates and the inclusion of PFGE-matched, but epidemiologically unrelated, isolates demonstrate the high resolution of WGS. The prevalence and enumeration data could contribute to our further understanding of the risk associated with Listeria monocytogenes contamination, especially among high-risk populations. Copyright © 2016 Chen et al.


July 7, 2019

Genomewide Dam methylation in Escherichia coli during long-term stationary phase.

DNA methylation in prokaryotes is widespread. The most common modification of the genome is the methylation of adenine at the N-6 position. In Escherichia coli K-12 and many gammaproteobacteria, this modification is catalyzed by DNA adenine methyltransferase (Dam) at the GATC consensus sequence and is known to modulate cellular processes including transcriptional regulation of gene expression, initiation of chromosomal replication, and DNA mismatch repair. While studies thus far have focused on the motifs associated with methylated adenine (meA), the frequency of meA across the genome, and temporal dynamics during early periods of incubation, here we conduct the first study on the temporal dynamics of adenine methylation in E. coli by Dam throughout all five phases of the bacterial life cycle in the laboratory. Using single-molecule real-time sequencing, we show that virtually all GATC sites are significantly methylated over time; nearly complete methylation of the chromosome was confirmed by mass spectroscopy analysis. However, we also detect 66 sites whose methylation patterns change significantly over time within a population, including three sites associated with sialic acid transport and catabolism, suggesting a potential role for Dam regulation of these genes; differential expression of this subset of genes was confirmed by quantitative real-time PCR. Further, we show significant growth defects of the dam mutant during long-term stationary phase (LTSP). Together these data suggest that the cell places a high premium on fully methylating the chromosome and that alterations in methylation patterns may have significant impact on patterns of transcription, maintenance of genetic fidelity, and cell survival. IMPORTANCE While it has been shown that methylation remains relatively constant into early stationary phase of E. coli, this study goes further through death phase and long-term stationary phase, a unique time in the bacterial life cycle due to nutrient limitation and strong selection for mutants with increased fitness. The absence of methylation at GATC sites can influence the mutation frequency within a population due to aberrant mismatch repair. Therefore, it is important to investigate the methylation status of GATC sites in an environment where cells may not prioritize methylation of the chromosome. This study demonstrates that chromosome methylation remains a priority even under conditions of nutrient limitation, indicating that continuous methylation at GATC sites could be under positive selection.


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