de.NBI Logo

Release Information: SILVA 91

Version 91 of the SSU and LSU databases as released on 13.08.2007


Parc 461,823 (+38,836) 85,689 (+11,834)
Ref 196,890 (+20,979) 6,902 (+560)


Click Opens internal link in current windowhere for SILVA 89 statistics.

Click Opens internal link in current windowhere for SILVA 90 statistics.

Sequence Retrieval and Processing

candidates 900,573 417,217
< 300 bases 320,327 297,218
> 2% ambiguities 8018 2193
> 2% homopolymers 19,240 4772
> 5% vector contamination 14,973 2573
rejected by SINA 75,024 20,591

rejected by:    

alignment quality < 30, and bp score < 30



Sequences have been retrieved from EMBL Opens external link in new windowRelease 91 (June 07) using a complex keyword search procedure. Cross checks with RDP II indicated no loss of primary data. Most of the sequences rejected by the new SINAligner were classified as not ribosomal RNA sequences by manual inspection or the remaining aligned sequence fragments were below 300 bases.

Small Subunit rRNA Database

SSU Parc (Web database & ARB file) contains all aligned sequences with an alignment quality value and a basepair score equal and above 30. No further curation has been applied.

To create SSU Ref (ARB file), aditionally all sequences below 1,200 bases for Bacteria and Eukarya and below 900 bases for Archaea or an alignment quality value below 50 have been removed from SSUParc. A guide tree was calculated by adding all sequences to the tree_1200 of SILVA release 90 which is based on tree_1000 from the ssujan04 release. For tree calculation, highly variable positions were removed for Bacteria, Archaea, and Eukarya with the respective position variability filters. Phyla and most of the classes for Bacteria and Archaea have been organized according to the Bergey's taxonomic outline. After manually inspection of the tree, around 213 sequences have been removed due to long branches. Position variability filters for Bacteria, Archaea and Eukarya have been calculated and added to the dataset. Please take into account that also sequences below an alignment quality value of 75 need further attention. All sequences with a Pintail value < 50 or an alignment quality value < 75 have been assigned to color group 1 in ARB (red). Before using the alignment for extensive phylogenetic reconstructions all sequences should be checked carefully.

Large Subunit rRNA Databases

LSUParc (Web database & ARB file) contains all aligned sequences with an alignment quality value and a basepair score equal and above 30. No further curation has been applied, only a guide tree has been added by the most parsimonious addition of 11,834 sequences to the LSUParc guide tree from SILVA 90.

Additionally, for LSURef (ARB file) all sequences below 1,900 bases have been removed, a guide tree was calculated based on the tree_1900 of SILVA release 90, and basic filters have been added. All sequences with an alignment quality value < 75 have been assigned to color group 1 in ARB (red). Please take into account that the SEED consisted only of around 2,800 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.

Update Cycle

For all four datasets, ARB change files are available in the Opens internal link in current windowdownload section. These datasets contain only sequences that are either new or the accession number has changed between SILVA release 90 and 91. 

Quality Values

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 Opens internal link in current windowFAQ section. Taking into account the rich set of sequence associated information that comes along with every SILVA sequence, user designed subdatabases can be easily generated.

Alternative 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 "Nomenclature up to date" catalogue (Opens external link in new window released in June 2007.

Alternative Taxonomies and Type Strain Information

Besides the EMBL Taxonomy, alternative classifications taken from the greengenes and the RDP II project are now 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: embl_tax, gg_tax and rdp_tax for EMBL, greengenes and RDP II, respectively. The corresponding *_name fields shows the respective sequence name for each entry.  Please take into account that both greengenes and RDP II provide only a subset of the sequences hosted by SILVA. If no taxonomic mapping to greengenes or RDP II was available they are assigned as "unclassified" and the respective sequence name equals EMBL. For the LSU datasets, there are no alternative taxonomies available. Type strain information has been added to the field strain and is indicated by [T]. Mapping was done based on the RDP II 9.51 dataset and is therefore only available for SSU Bacteria.


All rRNA sequences have been aligned based on a completely manually re-checked SEED alignment of 51,601 rRNA sequences for SSU and 2,868 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 by Katrin Knittel. 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. 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.

Known Bugs

  • Currently none.

Future Developments

Similarity based search and aligner functionalities are planned for mid of 2007. The SEED and Ref databases require further extension and curation.

Statistics: SILVA 91

1. Growth of the ribosomal RNA databases since 1992

 Initiates file download

Blue: RDP II, orange: SILVA SSUParc based on the EMBL release 91

2. Length Distribution (SSU & LSU)

Initiates file download

Red: raw data, black: the quality checked & aligned SSUParc sequences


Initiates file download

Red: raw data, black: the quality checked & aligned LSUParc sequences

3. Sequence quality in relation to length in SSUParc 90

Initiates file download

Basic statistics for the SILVA databases, release 91

    SSUParc   SSURef   LSUParc   LSURef  
Version   91   91   91   91  
Total   461,823   196,890   85,689   6902  
Bacteria   369,310   157,996   6751   3809  
Archaea   20,790   7932   145   138  
Eukarya   69,460   30,962   78793   2958  
Cultured #   147,980   84,717   78,680   6828  
Uncultured   313,843   112,173   7009   74  
Type strain   5054   5013   na   na  
# searched for not   matching   *uncult*   or *unident*   or *clone*  
in full name. Contains   false   positives.