Release information of the SILVA SSU and LSU databases 132 as of Dec 13, 2017

Former statistics:

SILVA 95, Silva 96, SILVA 98, SILVA 100, SILVA 102,

SILVA 104, SILVA 106, SILVA 108, SILVA 111, SILVA 115,

SILVA 119, SILVA 123, SILVA 128

SSU Parc (Web database only) contains all aligned sequences with an alignment identity value equal and above 50, an alignment quality value equal and above 40 as well as an basepair score or sequence quality equal and above 30. All sequences with a Pintail value < 50 or an alignment quality value < 75 have been assigned to color group 1 in ARB (red). All Living Tree Project or StrainInfo typestrains have been assigned to color group 2 in ARB (light blue). No further sequence curation has been applied.

To create SSU Ref (Web database & ARB file), all sequences below 1,200 bases for Bacteria and Eukarya and below 900 bases for Archaea or an alignment identity below 70 or an alignment quality value below 50 have been removed from SSU Parc. All sequences with a Pintail value < 50 or an alignment quality value < 75 have been assigned to color group 1 in ARB (red). All Living Tree Project or StrainInfo typestrains have been assigned to color group 2 in ARB (light blue).

To create SSU Ref NR 99 (Web database & ARB file), a 99% identity criterion to remove highly identical sequences using the UCLUST tool was applied. Sequences from cultivated species have been preserved in all cases. A guide tree was calculated by adding all sequences to the SSU Ref tree of SILVA release 128. For tree calculation, highly variable positions were removed for Bacteria, Archaea, and Eukarya with the respective position variability filters. Position variability filters for Bacteria, Archaea and Eukarya have been calculated and added to the dataset. The tree was extensively manually curated taking into account the latest taxonomic information. More information about the SILVA and LTP taxonomic frameworks can be found in the respective paper. Detailed information about the SSU Ref NR dataset is available here.

Remark: Before using the alignment for extensive phylogenetic reconstructions all sequences should be checked carefully.

LSU Parc (Web database & ARB file) contains all aligned sequences with an alignment identity value equal and above 40 and an alignment quality value, a basepair score or a sequence quality equal and above 30. All sequences with an alignment quality value < 75 have been assigned to color group 1 in ARB (red). All Living Tree Project or StrainInfo typestrains have been assigned to color group 2 in ARB (light blue). No further curation has been applied. 

Additionally, for LSU Ref (Web database & ARB file) all sequences below 1,900 bases or an alignment identity below 60 have been removed, a guide tree was calculated based on the LSU Ref tree of SILVA release 128, and basic filters have been added. The tree was manually curated taking into account the latest taxonomic information. More information about the SILVA and LTP taxonomic frameworks can be found in the respective paper.

Please take into account that the LSU SEED consists only of around 4508 sequences and there is no guaranty that well aligned close relatives have always been available. We would recommend additional manual curation before using it for extensive phylogenetic reconstructions.

Taxonomy

With SILVA release 102 the default taxonomy shown on the webpage (browser/search) is the SILVA taxonomy. Briefly, the tree for Bacteria and Archaea has been organized based on the Bergey's taxonomic outline, LPSN and the literature. Starting with SILVA release 111 extensive care has been taken to also improve the eukaryotic taxonomy. Based on the curated SILVA Ref taxonomy all sequences in SILVA (Parc) have been automatically classified.  

Alternative Taxonomies

Besides the SILVA and EMBL-EBI/ENA taxonomy, alternative classifications taken from the greengenes (May 2013), RDP II (July 2017) and LTP (Feb 2017) projects are also available in SILVA. On the webpage, the user can switch using the taxonomy menu. In ARB, the different taxonomies can be found in the fields: tax_slv, tax_embl, tax_gg, tax_rdp and tax_ltp for SILVA, EMBL-EBI/ENA, greengenes, RDP II and LTP, respectively. The corresponding *_name fields shows the respective sequence name for each entry.  Please take into account that greengenes, RDP II and LTP provide only a subset of the sequences hosted by SILVA. If no taxonomic mapping to greengenes, RDP II or LTP was available they are assigned as "unclassified" and the respective sequence name equals EMBL-EBI/ENA. For the LSU datasets only SILVA, LTP and EMBL-EBI/ENA taxonomies are available.

Altenative Names

All names of validly described species in the SSU and LSU databases have been checked for changes (basonyms, synonyms and orthographical corrections) against the DSMZ "Bacterial Nomenclature up to date (PNU)" service as of July 2017.

Cultured and Type strains

The information if a sequence originates from a cultured or type strain has been added to the field strain and is indicated by [T] and [C]. Several sources have been used to compile the information: The StrainInfo.net bioportal (July 2017), The Ribosomal Database Project II (July 2017) and the Living Tree Project (release 128) which provides manually curated information compliant with Euzebys "List of Prokaryotic names with Standing in Nomenclature".

Genomes

The information if a sequence originates from a genome project has been taken from EMBL-EBI/ENA and added to the field strain. It is indicated by e[G].

Detailed information about the corresponding identifiers and target databases can be found in the table to the right.

The identifiers can be used for data retrieval by searching in the strain field see FAQ.

The length and colours of the bars give a first indication on the sequence and alignment quality as well as the risk for sequence anomalies based on Pintail analysis. After downloading the sequences as an ARB file, sequences that need attention can be selected by searching for low quality (alignment, sequence) or Pintail values in the corresponding ARB database fields. A full description of the colour code and all database fields available in the ARB files can be found in the FAQ section. Taking into account the rich set of sequence associated information that comes along with every SILVA sequence, user designed sub-databases can be easily generated.

All rRNA sequences have been aligned based on a completely manually re-checked SEED alignment of 65,288 rRNA sequences for SSU and 4508 rRNA sequences for LSU. The SSU alignment is based on the official ssu_jan04 release of the ARB Project. The SSU SEED alignment has been considerably improved for Archaea by manual addition of more than 1,000 sequences as well as Fungi (10,000 sequences). All SSU Eukaryotic sequences (18S) have been cross-checked by Wolfgang Ludwig before their addition to the SEED. Most of the bacterial sequences have also undergone a curation process carried out by the SILVA Team. We would rate our SSU SEED alignment for all Bacteria and Archaea as good and for Eukarya as reasonable.

The LSU alignment was provided by Wolfgang Ludwig and has not been released before SILVA. It was cross-checked by the SILVA Team before using it as the SEED for automatic alignment.  Bacteria and Archaea could be rated as good. The Eukaryotes need definitely further attention. With SILVA release 128 the LSU SEED has been significantly expanded by the integration of the LSU LTP sequences (1217) and curated sequences from Fungi (1587) thanks to Katrin Panzer and Marlis Reich. 

Sequence Retrieval and Processing

Sequences have been retrieved from EMBL-EBI/ENA Release 132 (July 2017) using a complex keyword search procedure and sequence based search with RNAmmer profiles. Cross checks with RDP II indicated no loss of primary data. Most of the sequences rejected by a low identity value after alignment with SINA were classified as not ribosomal RNA sequences by manual inspection.

Blue: RDP II, orange: SILVA SSUParc based on EMBL releases

Blue: raw data, red: the quality checked & aligned SSUParc sequences

Blue: raw data, red: the quality checked & aligned LSUParc sequences

RNAmmer is a computational predictor for the major rRNA species (SSU, LSU) from all three domains of life. The program uses hidden Markov models trained on data from the European ribosomal RNA database project. SILVA runs the profiles of RNAmmer on all sequence entries of the EMBL-EBI/ENA archive to complement the existing predictions. All predictions are marked with RNAmmer in the ann_src_field. More information about RNAmmer can be found in the paper.

• Webpage
  • All SILVA sequences are automatically taxonomically classified based on LSURef and SSURef NR 99.
  • LTP updated to release 128.
  • Links to BacDive, DSMZ Catalogue and LPSN have been added where possible.
  • The SILVA Treeviewer has been published.
• ARB files
  
  • The guide tree is only available for SSU Ref NR 99 and LSU Ref.
• Exports
  • Mapping files for the SILVA taxonomy and ranks are now available for SSU and LSU.
  • Megan compatible files are now available.
• Pipeline
  • Several improvements and bug fixing.
  • Added more than 1000 sequences to the blacklist after manual inspection.
• Seed
  • Duplicates in SSU Seed were removed.
  • The SSU Seed now contains 65,288 sequences.
  • Duplicates in LSU Seed were removed.
  • The LSU Seed now contains 4508 sequences.
• SILVA
  • SILVA continuous to receive funding by the BMBF as part of the German Bioinformatics Network Infrastructure de.NBI.
  • A Mini-review about ARB and SILVA has been published.
• Taxonomy
  • Several errors in the bacterial, archaeal and eukaryotic taxonomy have been corrected.
  • Many taxonomic clusters have been evaluated for their stability.
  • Clean up of suspect bad quality/chimeric sequences.
  • Fungi taxonomy rearranged, mostly follows ncbi as this is currently the most reasonable.
  • Many phyla in bacteria are rearranged following the Genome Taxonomy Database.
  • Proteobacteria drastically rearranged. Epsilonproteobacteria are own phylum, Betaproteobacteria now an order of Gammaproteobacteria.
  • Candidate phyla radiation is under Parcubacteria.
  • Cyanobacteria taxonomy entirely redone, genus names are followed by strain ids to maintain genera uniqueness.
  • Many MAG rrnas in database, uncultured clade names updated to reflect mag names wherever appropriate.
  • SAR11 subclades redone.
  • Archaea higher level reflects upcoming Bergeys outline. Euryarchaea kept until we reach a decision in names.
  • General tree cleanup to remove anomalies.

• SSUParc: 117,695 sequences have no Pintail values