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Schmid M, Muri J, Melidis D, Varadarajan AR, Somerville V, Wicki A, Moser A, Bourqui M, Wenzel C, Eugster-Meier E, Frey JE, Irmler S, Ahrens CH. Comparative Genomics of Completely Sequenced Lactobacillus helveticus Genomes Provides Insights into Strain-Specific Genes and Resolves Metagenomics Data Down to the Strain Level. Front Microbiol 2018; 9:63. [PMID: 29441050 PMCID: PMC5797582 DOI: 10.3389/fmicb.2018.00063] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Accepted: 01/10/2018] [Indexed: 11/20/2022] Open
Abstract
Although complete genome sequences hold particular value for an accurate description of core genomes, the identification of strain-specific genes, and as the optimal basis for functional genomics studies, they are still largely underrepresented in public repositories. Based on an assessment of the genome assembly complexity for all lactobacilli, we used Pacific Biosciences' long read technology to sequence and de novo assemble the genomes of three Lactobacillus helveticus starter strains, raising the number of completely sequenced strains to 12. The first comparative genomics study for L. helveticus—to our knowledge—identified a core genome of 988 genes and sets of unique, strain-specific genes ranging from about 30 to more than 200 genes. Importantly, the comparison of MiSeq- and PacBio-based assemblies uncovered that not only accessory but also core genes can be missed in incomplete genome assemblies based on short reads. Analysis of the three genomes revealed that a large number of pseudogenes were enriched for functional Gene Ontology categories such as amino acid transmembrane transport and carbohydrate metabolism, which is in line with a reductive genome evolution in the rich natural habitat of L. helveticus. Notably, the functional Clusters of Orthologous Groups of proteins categories “cell wall/membrane biogenesis” and “defense mechanisms” were found to be enriched among the strain-specific genes. A genome mining effort uncovered examples where an experimentally observed phenotype could be linked to the underlying genotype, such as for cell envelope proteinase PrtH3 of strain FAM8627. Another possible link identified for peptidoglycan hydrolases will require further experiments. Of note, strain FAM22155 did not harbor a CRISPR/Cas system; its loss was also observed in other L. helveticus strains and lactobacillus species, thus questioning the value of the CRISPR/Cas system for diagnostic purposes. Importantly, the complete genome sequences proved to be very useful for the analysis of natural whey starter cultures with metagenomics, as a larger percentage of the sequenced reads of these complex mixtures could be unambiguously assigned down to the strain level.
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Affiliation(s)
- Michael Schmid
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland.,Swiss Institute of Bioinformatics, Wädenswil, Switzerland
| | - Jonathan Muri
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland
| | - Damianos Melidis
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland
| | - Adithi R Varadarajan
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland.,Swiss Institute of Bioinformatics, Wädenswil, Switzerland
| | - Vincent Somerville
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland.,Swiss Institute of Bioinformatics, Wädenswil, Switzerland
| | - Adrian Wicki
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland
| | - Aline Moser
- Agroscope, Research Group Biochemistry of Milk and Microorganisms, Bern, Switzerland
| | - Marc Bourqui
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland.,Swiss Institute of Bioinformatics, Wädenswil, Switzerland
| | - Claudia Wenzel
- Agroscope, Research Group Biochemistry of Milk and Microorganisms, Bern, Switzerland
| | - Elisabeth Eugster-Meier
- School of Agricultural, Forest and Food Sciences HAFL, Bern University of Applied Sciences, Zollikofen, Switzerland
| | - Juerg E Frey
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland
| | - Stefan Irmler
- Agroscope, Research Group Biochemistry of Milk and Microorganisms, Bern, Switzerland
| | - Christian H Ahrens
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics, Wädenswil, Switzerland.,Swiss Institute of Bioinformatics, Wädenswil, Switzerland
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Omasits U, Varadarajan AR, Schmid M, Goetze S, Melidis D, Bourqui M, Nikolayeva O, Québatte M, Patrignani A, Dehio C, Frey JE, Robinson MD, Wollscheid B, Ahrens CH. An integrative strategy to identify the entire protein coding potential of prokaryotic genomes by proteogenomics. Genome Res 2017; 27:2083-2095. [PMID: 29141959 PMCID: PMC5741054 DOI: 10.1101/gr.218255.116] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Accepted: 10/25/2017] [Indexed: 12/18/2022]
Abstract
Accurate annotation of all protein-coding sequences (CDSs) is an essential prerequisite to fully exploit the rapidly growing repertoire of completely sequenced prokaryotic genomes. However, large discrepancies among the number of CDSs annotated by different resources, missed functional short open reading frames (sORFs), and overprediction of spurious ORFs represent serious limitations. Our strategy toward accurate and complete genome annotation consolidates CDSs from multiple reference annotation resources, ab initio gene prediction algorithms and in silico ORFs (a modified six-frame translation considering alternative start codons) in an integrated proteogenomics database (iPtgxDB) that covers the entire protein-coding potential of a prokaryotic genome. By extending the PeptideClassifier concept of unambiguous peptides for prokaryotes, close to 95% of the identifiable peptides imply one distinct protein, largely simplifying downstream analysis. Searching a comprehensive Bartonella henselae proteomics data set against such an iPtgxDB allowed us to unambiguously identify novel ORFs uniquely predicted by each resource, including lipoproteins, differentially expressed and membrane-localized proteins, novel start sites and wrongly annotated pseudogenes. Most novelties were confirmed by targeted, parallel reaction monitoring mass spectrometry, including unique ORFs and single amino acid variations (SAAVs) identified in a re-sequenced laboratory strain that are not present in its reference genome. We demonstrate the general applicability of our strategy for genomes with varying GC content and distinct taxonomic origin. We release iPtgxDBs for B. henselae, Bradyrhizobium diazoefficiens and Escherichia coli and the software to generate both proteogenomics search databases and integrated annotation files that can be viewed in a genome browser for any prokaryote.
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Affiliation(s)
- Ulrich Omasits
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
| | - Adithi R Varadarajan
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland.,Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland
| | - Michael Schmid
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
| | - Sandra Goetze
- Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland
| | - Damianos Melidis
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
| | - Marc Bourqui
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
| | - Olga Nikolayeva
- Institute for Molecular Life Sciences & SIB Swiss Institute of Bioinformatics, University of Zurich, CH-8057 Zurich, Switzerland
| | | | - Andrea Patrignani
- Functional Genomics Center Zurich, ETH & UZH Zurich, CH-8057 Zurich, Switzerland
| | | | - Juerg E Frey
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
| | - Mark D Robinson
- Institute for Molecular Life Sciences & SIB Swiss Institute of Bioinformatics, University of Zurich, CH-8057 Zurich, Switzerland
| | - Bernd Wollscheid
- Department of Health Sciences and Technology, Institute of Molecular Systems Biology, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland
| | - Christian H Ahrens
- Agroscope, Research Group Molecular Diagnostics, Genomics and Bioinformatics & SIB Swiss Institute of Bioinformatics, CH-8820 Wädenswil, Switzerland
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