Penicillium species cause postharvest decay, commonly known as blue mold, in pome fruits, such as apples and pears. To devise novel strategies to prevent and reduce economic losses during storage, the genome sequence of Penicillium solitum RS1 is reported here for the first time. Copyright © 2016 Yu et al.
Hafnia alvei is a facultative and rod-shaped gram-negative bacterium that belongs to the Enterobacteriaceae family. Although it has been more than 50 years since the genus was identified, very little is known about variations among Hafnia species. Diversity in O-antigens (O-polysaccharide, OPS) is thought to be a major factor in bacterial adaptation to different hosts and situations and variability in the environment. Antigenic variation is also an important factor in pathogenicity that has been used to define clones within a number of species. The genes that are required to synthesize OPS are always clustered within the bacterial chromosome. A serotyping scheme including 39 O-serotypes has been proposed for H. alvei, but it has not been correlated with known OPS structures, and no previous report has described the genetic features of OPS. In this study, we obtained the genome sequences of 21 H. alvei strains (as defined by previous immunochemical studies) with different lipopolysaccharides. This is the first study to show that the O-antigen gene cluster in H. alvei is located between mpo and gnd in the chromosome. All 21 of the OPS gene clusters contain both the wzx gene and the wzy gene and display a large number of polymorphisms. We developed an O serotype-specific wzy-based suspension array to detect all 21 of the distinct OPS forms we identified in H. alvei. To the best of our knowledge, this is the first report to identify the genetic features of H. alvei antigenic variation and to develop a molecular technique to identify and classify different serotypes.
Host adaptation is a key factor contributing to the emergence of new bacterial, viral and parasitic pathogens. Many pathogens are considered promiscuous because they cause disease across a range of host species, while others are host-adapted, infecting particular hosts(1). Host adaptation can potentially progress to host restriction where the pathogen is strictly limited to a single host species and is frequently associated with more severe symptoms. Host-adapted and host-restricted bacterial clades evolve from within a broader host-promiscuous species and sometimes target different niches within their specialist hosts, such as adapting from a mucosal to a systemic lifestyle. Genome degradation, marked by gene inactivation and deletion, is a key feature of host adaptation, although the triggers initiating genome degradation are not well understood. Here, we show that a chronic systemic non-typhoidal Salmonella infection in an immunocompromised human patient resulted in genome degradation targeting genes that are expendable for a systemic lifestyle. We present a genome-based investigation of a recurrent blood-borne Salmonella enterica serotype Enteritidis (S. Enteritidis) infection covering 15 years in an interleukin (IL)-12 ß-1 receptor-deficient individual that developed into an asymptomatic chronic infection. The infecting S. Enteritidis harbored a mutation in the mismatch repair gene mutS that accelerated the genomic mutation rate. Phylogenetic analysis and phenotyping of multiple patient isolates provides evidence for a remarkable level of within-host evolution that parallels genome changes present in successful host-restricted bacterial pathogens but never before observed on this timescale. Our analysis identifies common pathways of host adaptation and demonstrates the role that immunocompromised individuals can play in this process.
The recent breakthroughs in assembling long error-prone reads were based on the overlap-layout-consensus (OLC) approach and did not utilize the strengths of the alternative de Bruijn graph approach to genome assembly. Moreover, these studies often assume that applications of the de Bruijn graph approach are limited to short and accurate reads and that the OLC approach is the only practical paradigm for assembling long error-prone reads. We show how to generalize de Bruijn graphs for assembling long error-prone reads and describe the ABruijn assembler, which combines the de Bruijn graph and the OLC approaches and results in accurate genome reconstructions.
The smut fungi form a large, diverse, and non-monophyletic group of plant pathogens that have long served as both important pests of human agriculture but also as fertile organisms of scientific investigation. As modern techniques of molecular genetic analysis became available, many previously-studied species that proved refractive to these techniques fell by the wayside to become neglected. Now, as the advent of rapid and affordable next-generation sequencing provides genomic and transcriptomic resources for even these “forgotten” fungi, several species are making a come-back and retaking prominent places in phytopathogenic research. In this review, we highlight several of these smut fungi, with special emphasis on Microbotryum lychnidis-dioicae, an anther smut, whose molecular genetic tools have finally begun to catch up with its historical importance in classical genetics and now provide mechanistic insights for ecological studies, evolution of host/pathogen interaction, and investigations of emerging infectious disease.
Enterococcus faecium infections are a rising concern in hospital settings. Vancomycin-resistant enterococci colonize the gastrointestinal tract and replace nonresistant strains, complicating the treatment of debilitated patients. Here, we present a polished genome of the multiantibiotic-resistant strain C68, which was obtained as a clinical isolate and is a useful experimental strain. Copyright © 2016 García-Solache and Rice.
The draft genomes of Thermus tengchongensis YIM 77401 and T. caliditerrae YIM 77777 are 2,562,314 and 2,218,114 bp and encode 2,726 and 2,305 predicted genes, respectively. Gene content and growth experiments demonstrate broad metabolic capacity, including starch hydrolysis, thiosulfate oxidation, arsenite oxidation, incomplete denitrification, and polysulfide reduction. Copyright © 2016 Mefferd et al.
We present the first genome sequence for a strain of the main mycetoma causative agent, Madurella mycetomatis This 36.7-Mb genome sequence will offer new insights into the pathogenesis of mycetoma, and it will contribute to the development of better therapies for this neglected tropical disease. Copyright © 2016 Smit et al.
Microevolution associated with emergence and expansion of new epidemic clones of bacterial pathogens holds the key to epidemiologic success. To determine microevolution associated with monophasic Salmonella Typhimurium during an epidemic, we performed comparative whole-genome sequencing and phylogenomic analysis of isolates from the United Kingdom and Italy during 2005-2012. These isolates formed a single clade distinct from recent monophasic epidemic clones previously described from North America and Spain. The UK monophasic epidemic clones showed a novel genomic island encoding resistance to heavy metals and a composite transposon encoding antimicrobial drug resistance genes not present in other Salmonella Typhimurium isolates, which may have contributed to epidemiologic success. A remarkable amount of genotypic variation accumulated during clonal expansion that occurred during the epidemic, including multiple independent acquisitions of a novel prophage carrying the sopE gene and multiple deletion events affecting the phase II flagellin locus. This high level of microevolution may affect antigenicity, pathogenicity, and transmission.
Catfish represent 12% of teleost or 6.3% of all vertebrate species, and are of enormous economic value. Here we report a high-quality reference genome sequence of channel catfish (Ictalurus punctatus), the major aquaculture species in the US. The reference genome sequence was validated by genetic mapping of 54,000 SNPs, and annotated with 26,661 predicted protein-coding genes. Through comparative analysis of genomes and transcriptomes of scaled and scaleless fish and scale regeneration experiments, we address the genomic basis for the most striking physical characteristic of catfish, the evolutionary loss of scales and provide evidence that lack of secretory calcium-binding phosphoproteins accounts for the evolutionary loss of scales in catfish. The channel catfish reference genome sequence, along with two additional genome sequences and transcriptomes of scaled catfishes, provide crucial resources for evolutionary and biological studies. This work also demonstrates the power of comparative subtraction of candidate genes for traits of structural significance.
The necrotrophic fungal pathogen Sclerotinia trifoliorum exhibits ascospore dimorphism and unidirectional mating type switching – self-fertile strains derived from large ascospores produce both self-fertile (large-spores) and self-sterile (small-spores) offsprings in a 4:4 ratio. The present study, comparing DNA sequences at MAT locus of both self-fertile and self-sterile strains, found four mating type genes (MAT1-1-1, MAT1-1-5, MAT1-2-1 and MAT1-2-4) in the self-fertile strain. However, a 2891-bp region including the entire MAT1-2-1 and MAT1-2-4 genes had been completely deleted from the MAT locus in the self-sterile strain. Meanwhile, two copies of a 146-bp direct repeat motif flanking the deleted region were found in the self-fertile strain, but only one copy of this 146-bp motif (a part of the MAT1-1-1 gene) was present in the self-sterile strain. The two direct repeats were believed to be responsible for the deletion through homologous intra-molecular recombination in meiosis. Tetrad analyses showed that all small ascospore-derived strains lacked the missing DNA between the two direct repeats that was found in all large ascospore-derived strains. In addition, heterokaryons at the MAT locus were observed in field isolates as well as in laboratory derived isolates.
Establishing an association between possible food sources and clinical isolates requires discriminating the suspected pathogen from an environmental background, and distinguishing it from other closely-related foodborne pathogens. We used whole genome sequencing (WGS) to Salmonella subspecies enterica serotype Tennessee (S. Tennessee) to describe genomic diversity across the serovar as well as among and within outbreak clades of strains associated with contaminated peanut butter. We analyzed 71 isolates of S. Tennessee from disparate food, environmental, and clinical sources and 2 other closely-related Salmonella serovars as outgroups (S. Kentucky and S. Cubana), which were also shot-gun sequenced. A whole genome single nucleotide polymorphism (SNP) analysis was performed using a maximum likelihood approach to infer phylogenetic relationships. Several monophyletic lineages of S. Tennessee with limited SNP variability were identified that recapitulated several food contamination events. S. Tennessee clades were separated from outgroup salmonellae by more than sixteen thousand SNPs. Intra-serovar diversity of S. Tennessee was small compared to the chosen outgroups (1,153 SNPs), suggesting recent divergence of some S. Tennessee clades. Analysis of all 1,153 SNPs structuring an S. Tennessee peanut butter outbreak cluster revealed that isolates from several food, plant, and clinical isolates were very closely related, as they had only a few SNP differences between them. SNP-based cluster analyses linked specific food sources to several clinical S. Tennessee strains isolated in separate contamination events. Environmental and clinical isolates had very similar whole genome sequences; no markers were found that could be used to discriminate between these sources. Finally, we identified SNPs within variable S. Tennessee genes that may be useful markers for the development of rapid surveillance and typing methods, potentially aiding in traceback efforts during future outbreaks. Using WGS can delimit contamination sources for foodborne illnesses across multiple outbreaks and reveal otherwise undetected DNA sequence differences essential to the tracing of bacterial pathogens as they emerge.
Nontyphoidal Salmonella species are globally disseminated pathogens and the predominant cause of gastroenteritis. The pathogenesis of salmonellosis has been extensively studied using in vivo murine models and cell lines typically challenged with Salmonella Typhimurium. Although serovars Enteritidis and Typhimurium are responsible for the most of human infections reported to the CDC, several other serovars also contribute to clinical cases of salmonellosis. Despite their epidemiological importance, little is known about their infection phenotypes. Here, we report the virulence characteristics and genomes of 10 atypical S. enterica serovars linked to multistate foodborne outbreaks in the United States. We show that the murine RAW 264.7 macrophage model of infection is unsuitable for inferring human relevant differences in nontyphoidal Salmonella infections whereas differentiated human THP-1 macrophages allowed these isolates to be further characterised in a more relevant, human context.
The recently isolated strain L21-Fru-AB(T) represents moderately halophilic, obligately anaerobic and saccharolytic bacteria that thrive in the suboxic transition zones of hypersaline microbial mats. Phylogenetic analyses based on 16S rRNA genes, RpoB proteins and gene content indicated that strain L21-Fru-AB(T) represents a novel species and genus affiliated with a distinct phylum-level lineage originally designated Verrucomicrobia subdivision 5. A survey of environmental 16S rRNA gene sequences revealed that members of this newly recognized phylum are wide-spread and ecologically important in various anoxic environments ranging from hypersaline sediments to wastewater and the intestine of animals. Characteristic phenotypic traits of the novel strain included the formation of extracellular polymeric substances, a Gram-negative cell wall containing peptidoglycan and the absence of odd-numbered cellular fatty acids. Unusual metabolic features deduced from analysis of the genome sequence were the production of sucrose as osmoprotectant, an atypical glycolytic pathway lacking pyruvate kinase and the synthesis of isoprenoids via mevalonate. On the basis of the analyses of phenotypic, genomic and environmental data, it is proposed that strain L21-Fru-AB(T) and related bacteria are specifically adapted to the utilization of sulfated glycopolymers produced in microbial mats or biofilms.
Very few closed genomes of the cyanobacteria that commonly produce toxic blooms in lakes and reservoirs are available, limiting our understanding of the properties of these organisms. A new anatoxin-a-producing member of the Nostocaceae, Anabaena sp. WA102, was isolated from a freshwater lake in Washington State, USA, in 2013 and maintained in non-axenic culture.The Anabaena sp. WA102 5.7 Mbp genome assembly has been closed with long-read, single-molecule sequencing and separately a draft genome assembly has been produced with short-read sequencing technology. The closed and draft genome assemblies are compared, showing a correlation between long repeats in the genome and the many gaps in the short-read assembly. Anabaena sp. WA102 encodes anatoxin-a biosynthetic genes, as does its close relative Anabaena sp. AL93 (also introduced in this study). These strains are distinguished by differences in the genes for light-harvesting phycobilins, with Anabaena sp. AL93 possessing a phycoerythrocyanin operon. Biologically relevant structural variants in the Anabaena sp. WA102 genome were detected only by long-read sequencing: a tandem triplication of the anaBCD promoter region in the anatoxin-a synthase gene cluster (not triplicated in Anabaena sp. AL93) and a 5-kbp deletion variant present in two-thirds of the population. The genome has a large number of mobile elements (160). Strikingly, there was no synteny with the genome of its nearest fully assembled relative, Anabaena sp. 90.Structural and functional genome analyses indicate that Anabaena sp. WA102 has a flexible genome. Genome closure, which can be readily achieved with long-read sequencing, reveals large scale (e.g., gene order) and local structural features that should be considered in understanding genome evolution and function.
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