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      SISP: a Fast Species Identification System for Prokaryotes Based on Total Nucleotide Identity of Whole Genome Sequences

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          Abstract

          In the genomic era, new techniques and criteria are proposed to improve the traditionally phenotypic and biochemical test–based approaches for prokaryotic species definition. Among them, average nucleotide identity (ANI) mirrors DNA-DNA hybridization and is widely used by the microbial research community. However, our test shows that ANI possibly defines distinct taxa as the same species when they shared highly homologous sequences in a very short genomic region. In this study, we propose an improved algorithm named total nucleotide identity (TNI) for use in bacterial taxonomy; this algorithm provided higher accuracy for species classification than ANI. Furthermore, we developed a species identification system for prokaryotes (SISP) based on pairwise TNI of 3,073 genomes acquired from GenBank. For a submitted query genome, SISP can quickly find its most closely related genome from the established database based on the TNI calculation and infer the possible species of the query genome. Given a criterion of TNI > 70%, SISP has an accuracy that was above 90% for 3,596 prokaryotic genomes. SISP is open source and is available at https://github.com/chjp/SISProkaryotes.

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          Performance comparison of benchtop high-throughput sequencing platforms.

          Three benchtop high-throughput sequencing instruments are now available. The 454 GS Junior (Roche), MiSeq (Illumina) and Ion Torrent PGM (Life Technologies) are laser-printer sized and offer modest set-up and running costs. Each instrument can generate data required for a draft bacterial genome sequence in days, making them attractive for identifying and characterizing pathogens in the clinical setting. We compared the performance of these instruments by sequencing an isolate of Escherichia coli O104:H4, which caused an outbreak of food poisoning in Germany in 2011. The MiSeq had the highest throughput per run (1.6 Gb/run, 60 Mb/h) and lowest error rates. The 454 GS Junior generated the longest reads (up to 600 bases) and most contiguous assemblies but had the lowest throughput (70 Mb/run, 9 Mb/h). Run in 100-bp mode, the Ion Torrent PGM had the highest throughput (80–100 Mb/h). Unlike the MiSeq, the Ion Torrent PGM and 454 GS Junior both produced homopolymer-associated indel errors (1.5 and 0.38 errors per 100 bases, respectively).
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            Defining bacterial species in the genomic era: insights from the genus Acinetobacter

            Background Microbial taxonomy remains a conservative discipline, relying on phenotypic information derived from growth in pure culture and techniques that are time-consuming and difficult to standardize, particularly when compared to the ease of modern high-throughput genome sequencing. Here, drawing on the genus Acinetobacter as a test case, we examine whether bacterial taxonomy could abandon phenotypic approaches and DNA-DNA hybridization and, instead, rely exclusively on analyses of genome sequence data. Results In pursuit of this goal, we generated a set of thirteen new draft genome sequences, representing ten species, combined them with other publically available genome sequences and analyzed these 38 strains belonging to the genus. We found that analyses based on 16S rRNA gene sequences were not capable of delineating accepted species. However, a core genome phylogenetic tree proved consistent with the currently accepted taxonomy of the genus, while also identifying three misclassifications of strains in collections or databases. Among rapid distance-based methods, we found average-nucleotide identity (ANI) analyses delivered results consistent with traditional and phylogenetic classifications, whereas gene content based approaches appear to be too strongly influenced by the effects of horizontal gene transfer to agree with previously accepted species. Conclusion We believe a combination of core genome phylogenetic analysis and ANI provides an appropriate method for bacterial species delineation, whereby bacterial species are defined as monophyletic groups of isolates with genomes that exhibit at least 95% pair-wise ANI. The proposed method is backwards compatible; it provides a scalable and uniform approach that works for both culturable and non-culturable species; is faster and cheaper than traditional taxonomic methods; is easily replicable and transferable among research institutions; and lastly, falls in line with Darwin’s vision of classification becoming, as far as is possible, genealogical.
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              On the origin of prokaryotic species.

              The notion that all prokaryotes belong to genomically and phenomically cohesive clusters that we might legitimately call "species" is a contentious one. At issue are (1) whether such clusters actually exist; (2) what species definition might most reliably identify them, if they do; and (3) what species concept -- by which is meant a genetic and ecological theory of speciation -- might best explain species existence and rationalize a species definition, if we could agree on one. We review existing theories and some relevant data. We conclude that microbiologists now understand in some detail the various genetic, population, and ecological processes that effect the evolution of prokaryotes. There will be on occasion circumstances under which these, working together, will form groups of related organisms sufficiently like each other that we might all agree to call them "species," but there is no reason that this must always be so. Thus, there is no principled way in which questions about prokaryotic species, such as how many there are, how large their populations are, or how globally they are distributed, can be answered. These questions can, however, be reformulated so that metagenomic methods and thinking will meaningfully address the biological patterns and processes whose understanding is our ultimate target.
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                Author and article information

                Contributors
                Journal
                Infectious Diseases and Translational Medicine
                Infect. Dis. Transl. Med.
                Infect. Dis. Transl. Med.
                International Biological and Medical Journals Publishing House Co., Limited (Room E16, 3/f, Yongda Commercial Building, No.97, Bonham Stand (Sheung Wan), HongKong )
                2411-2917
                30 June 2015
                10 June 2015
                : 1
                : 1
                : 30-55
                Affiliations
                From State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China; Beijing Genomics Institute, Shenzhen, China
                From State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China
                Beijing Genomics Institute, Shenzhen, China
                Beijing Genomics Institute, Shenzhen, China
                From State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China
                Beijing Genomics Institute, Shenzhen, China
                From State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China
                Author notes
                Correspondence to: Yujun Cui, from State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, China; Email: cuiyujun.new@ 123456gmail.com .
                Article
                10.11979/idtm.201501008
                832eb1f6-8a41-4b63-8ff6-c916506ca65a

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                Page count
                Figures: 3, Tables: 3, References: 9, Pages: 26
                Product
                Categories
                Original Article

                Medicine,Infectious disease & Microbiology
                Molecular typing,Nucleotide identity,Taxonomy,Species definition,Whole genome sequencing

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