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July 7, 2019  |  

Large-scale maps of variable infection efficiencies in aquatic Bacteroidetes phage-host model systems.

Microbes drive ecosystem functioning and their viruses modulate these impacts through mortality, gene transfer and metabolic reprogramming. Despite the importance of virus-host interactions and likely variable infection efficiencies of individual phages across hosts, such variability is seldom quantified. Here, we quantify infection efficiencies of 38 phages against 19 host strains in aquatic Cellulophaga (Bacteroidetes) phage-host model systems. Binary data revealed that some phages infected only one strain while others infected 17, whereas quantitative data revealed that efficiency of infection could vary 10 orders of magnitude, even among phages within one population. This provides a baseline for understanding and modeling intrapopulation host range variation. Genera specific host ranges were also informative. For example, the Cellulophaga Microviridae, showed a markedly broader intra-species host range than previously observed in Escherichia coli systems. Further, one phage genus, Cba41, was examined to investigate nonheritable changes in plating efficiency and burst size that depended on which host strain it most recently infected. While consistent with host modification of phage DNA, no differences in nucleotide sequence or DNA modifications were detected, leaving the observation repeatable, but the mechanism unresolved. Overall, this study highlights the importance of quantitatively considering replication variations in studies of phage-host interactions. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

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July 7, 2019  |  

Ectomycorrhizal ecology is imprinted in the genome of the dominant symbiotic fungus Cenococcum geophilum.

The most frequently encountered symbiont on tree roots is the ascomycete Cenococcum geophilum, the only mycorrhizal species within the largest fungal class Dothideomycetes, a class known for devastating plant pathogens. Here we show that the symbiotic genomic idiosyncrasies of ectomycorrhizal basidiomycetes are also present in C. geophilum with symbiosis-induced, taxon-specific genes of unknown function and reduced numbers of plant cell wall-degrading enzymes. C. geophilum still holds a significant set of genes in categories known to be involved in pathogenesis and shows an increased genome size due to transposable elements proliferation. Transcript profiling revealed a striking upregulation of membrane transporters, including aquaporin water channels and sugar transporters, and mycorrhiza-induced small secreted proteins (MiSSPs) in ectomycorrhiza compared with free-living mycelium. The frequency with which this symbiont is found on tree roots and its possible role in water and nutrient transport in symbiosis calls for further studies on mechanisms of host and environmental adaptation.

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July 7, 2019  |  

Genomic, physiologic, and proteomic insights into metabolic versatility in Roseobacter clade bacteria isolated from deep-sea water.

Roseobacter clade bacteria are ubiquitous in marine environments and now thought to be significant contributors to carbon and sulfur cycling. However, only a few strains of roseobacters have been isolated from the deep-sea water column and have not been thoroughly investigated. Here, we present the complete genomes of phylogentically closed related Thiobacimonas profunda JLT2016 and Pelagibaca abyssi JLT2014 isolated from deep-sea water of the Southeastern Pacific. The genome sequences showed that the two deep-sea roseobacters carry genes for versatile metabolisms with functional capabilities such as ribulose bisphosphate carboxylase-mediated carbon fixation and inorganic sulfur oxidation. Physiological and biochemical analysis showed that T. profunda JLT2016 was capable of autotrophy, heterotrophy, and mixotrophy accompanied by the production of exopolysaccharide. Heterotrophic carbon fixation via anaplerotic reactions contributed minimally to bacterial biomass. Comparative proteomics experiments showed a significantly up-regulated carbon fixation and inorganic sulfur oxidation associated proteins under chemolithotrophic conditions compared to heterotrophic conditions. Collectively, rosebacters show a high metabolic flexibility, suggesting a considerable capacity for adaptation to the marine environment.

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July 7, 2019  |  

Complete genome of Vibrio parahaemolyticus FORC014 isolated from the toothfish.

Foodborne illness can occur due to various pathogenic bacteria such as Staphylococcus aureus, Escherichia coli and Vibrio parahaemolyticus, and can cause severe gastroenteritis symptoms. In this study, we completed the genome sequence of a foodborne pathogen V. parahaemolyticus FORC_014, which was isolated from suspected contaminated toothfish from South Korea. Additionally, we extended our knowledge of genomic characteristics of the FORC_014 strain through comparative analysis using the complete sequences of other V. parahaemolyticus strains whose complete genomes have previously been reported.The complete genome sequence of V. parahaemolyticus FORC_014 was generated using the PacBio RS platform with single molecule, real-time (SMRT) sequencing. The FORC_014 strain consists of two circular chromosomes (3,241,330 bp for chromosome 1 and 1,997,247 bp for chromosome 2), one plasmid (51,383 bp), and one putative phage sequence (96,896 bp). The genome contains a total of 4274 putative protein coding sequences, 126 tRNA genes and 34 rRNA genes. Furthermore, we found 33 type III secretion system 1 (T3SS1) related proteins and 15 type III secretion system 2 (T3SS2) related proteins on chromosome 1. This is the first reported result of Type III secretion system 2 located on chromosome 1 of V. parahaemolyticus without thermostable direct hemolysin (tdh) and thermostable direct hemolysin-related hemolysin (trh).Through investigation of the complete genome sequence of V. parahaemolyticus FORC_014, which differs from previously reported strains, we revealed two type III secretion systems (T3SS1, T3SS2) located on chromosome 1 which do not include tdh and trh genes. We also identified several virulence factors carried by our strain, including iron uptake system, hemolysin and secretion system. This result suggests that the FORC_014 strain may be one pathogen responsible for foodborne illness outbreak. Our results provide significant genomic clues which will assist in future understanding of virulence at the genomic level and help distinguish between clinical and non-clinical isolates.

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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.

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July 7, 2019  |  

Origins of the current seventh cholera pandemic.

Vibrio cholerae has caused seven cholera pandemics since 1817, imposing terror on much of the world, but bacterial strains are currently only available for the sixth and seventh pandemics. The El Tor biotype seventh pandemic began in 1961 in Indonesia, but did not originate directly from the classical biotype sixth-pandemic strain. Previous studies focused mainly on the spread of the seventh pandemic after 1970. Here, we analyze in unprecedented detail the origin, evolution, and transition to pandemicity of the seventh-pandemic strain. We used high-resolution comparative genomic analysis of strains collected from 1930 to 1964, covering the evolution from the first available El Tor biotype strain to the start of the seventh pandemic. We define six stages leading to the pandemic strain and reveal all key events. The seventh pandemic originated from a nonpathogenic strain in the Middle East, first observed in 1897. It subsequently underwent explosive diversification, including the spawning of the pandemic lineage. This rapid diversification suggests that, when first observed, the strain had only recently arrived in the Middle East, possibly from the Asian homeland of cholera. The lineage migrated to Makassar, Indonesia, where it gained the important virulence-associated elements Vibrio seventh pandemic island I (VSP-I), VSP-II, and El Tor type cholera toxin prophage by 1954, and it then became pandemic in 1961 after only 12 additional mutations. Our data indicate that specific niches in the Middle East and Makassar were important in generating the pandemic strain by providing gene sources and the driving forces for genetic events.

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July 7, 2019  |  

Genome sequence resources for the wheat stripe rust pathogen (Puccinia striiformis f. sp. tritici) and the barley stripe rust pathogen (Puccinia striiformis f. sp. hordei)

Puccinia striiformis f. sp. tritici causes devastating stripe (yellow) rust on wheat and P. striiformis f. sp. hordei causes stripe rust on barley. Several P. striiformis f. sp. tritici genomes are available, but no P. striiformis f. sp. hordei genome is available. More genomes of P. striiformis f. sp. tritici and P. striiformis f. sp. hordei are needed to understand the genome evolution and molecular mechanisms of their pathogenicity. We sequenced P. striiformis f. sp. tritici isolate 93-210 and P. striiformis f. sp. hordei isolate 93TX-2, using PacBio and Illumina technologies and RNA sequencing. Their genomic sequences were assembled to contigs with high continuity and showed significant structural differences. The circular mitochondria genomes of both were complete. These genomes provide high-quality resources for deciphering the genomic basis of rapid evolution and host adaptation, identifying genes for avirulence and other important traits, and studying host-pathogen interactions.

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