Complete genome sequence of Bacteroides salanitronis type strain (BL78T)

Bacteroides salanitronis Lan et al. 2006 is a species of the genus Bacteroides, which belongs to the family Bacteroidaceae. The species is of interest because it was isolated from the gut of a chicken and the growing awareness that the anaerobic microflora of the cecum is of benefit for the host and may impact poultry farming. The 4,308,663 bp long genome consists of a 4.24 Mbp chromosome and three plasmids (6 kbp, 19 kbp, 40 kbp) containing 3,737 protein-coding and 101 RNA genes and is a part of the Genomic Encyclopedia of Bacteria and Archaea project.


Introduction
Strain BL78 T (= DSM 18170 = CCUG 54637 = JCM 13657) is the type strain of Bacteroides salanitronis which belongs to the large genus Bacteroides [1,2]. Currently, there are 88 species placed in the genus Bacteroides. The species epithet is derived from the name of Joseph P. Salanitro, an American microbiologist. B. salanitronis strain BL78 T was isolated among other Bacteroides strains from the cecum of a healthy chicken. No other strain belonging to the same species has been identified [2]. Many Bacteroides species are common inhabitants of the intestine where they help to degrade complex molecules such as polysaccharides or transform steroids [3,4]. They also play a role as beneficent protectors of the gut against pathogenic microorganisms [5]. Here we present a sum-mary classification and a set of features for B. salanitronis BL78 T , together with the description of the complete genomic sequencing and annotation.

Classification and features
A representative genomic 16S rRNA sequence of strain BL78 T was compared using NCBI BLAST under default settings (e.g., considering only the highscoring segment pairs (HSPs) from the best 250 hits) with the most recent release of the Greengenes database [6] and the relative frequencies, weighted by BLAST scores, of taxa and keywords (reduced to their stem [7]) were determined. The single most frequent genus was Bacteroides (100.0%) (1 hit in total). Regarding the single hit to sequences from members of the species, the average identity within HSPs was 99.7%, whereas the average coverage by HSPs was 96.2%. No hits to sequences with (other) species names were found. The highest-scoring environmental sequence was DQ456041 ('preadolescent turkey cecum clone CFT112F11'), which showed an identity of 96.8% and an HSP coverage of 63.9%. The five most frequent keywords within the labels of environmental samples which yielded hits were 'fecal' (9.3%), 'microbiota' (7.5%), 'human' (7.1%), 'antibiot, effect, gut, pervas' (7.1%) and 'anim, beef, cattl, coli, escherichia, feedlot, habitat, synecolog' (2.2%) (249 hits in total). Figure 1 shows the phylogenetic neighborhood of B. salanitronis in a 16S rRNA based tree. The sequences of the six 16S rRNA gene copies in the genome differ from each other by up to 26 nucleotides, and differ by up to 26 nucleotides from the previously published 16S rRNA sequence (AB253731). The cells of B. salanitronis are generally rod-shaped (0.4-0.7 × 0.8-5.6 µm) with rounded ends (Figure 2). The cells are usually arranged singly or in pairs [2]. B. salanitronis is a Gram-negative, non-sporeforming bacterium (Table 1) that is described as non-motile, with only five genes associated with motility having been found in the genome (see below).
The temperature optimum for strain BL78 T is 37°C. B. salanitronis is a strictly anaerobic chemoorganotroph and is able to ferment glucose, mannose, sucrose, maltose, arabinose, cellobiose, lactose, xylose and raffinose [2]. The organism hydrolyzes esculin but does not liquefy gelatin, and neither reduces nitrate nor produces indole from tryptophan [2]. B. salanitronis does not utilize trehalose, glycerol, mannitol, sorbitol or melezitose; rhamnose and salicin are fermented weakly [2]. Growth is possible in the presence of bile [2]. Major fermentation products from broth (1% peptone, 1% yeast extract, and 1% glucose each (w/v)) are acetic acid and succinic acid, whereas isovaleric acid is produced in small amounts [2]. B. salanitronis shows activity for alkaline phosphatase, α-and β-galactosidases, α-and βglucosidases, α-arabinosidase, leucyl glycine arylamidase, alanine arylamidase and glutamyl glutamic acid arylamidase but no activity for urease, catalase, glutamic acid decarboxylase, arginine dihydrolase, β-galactosidase 6-phosphate, β-glucuronidase, Nacetyl-β-glucosaminidase, α-fucosidase and arginine, proline, leucine, phenylalanine, pyroglutamic acid, tyrosine, glycine, histidine and serine arylamidase [2].  [8,9] of the 16S rRNA gene sequence under the maximum likelihood criterion [10] and rooted in accordance with the current taxonomy. The branches are scaled in terms of the expected number of substitutions per site. Numbers to the right of bifurcations are support values from 1,000 bootstrap replicates [11] if larger than 60%. Lineages with type strain genome sequencing projects registered in GOLD [12] but unpublished are labeled with one asterisk, published genomes with two asterisks [13][14][15].  Altitude not reported Evidence codes -IDA: Inferred from Direct Assay (first time in publication); TAS: Traceable Author Statement (i.e., a direct report exists in the literature); NAS: Non-traceable Author Statement (i.e., not directly observed for the living, isolated sample, but based on a generally accepted property for the species, or anecdotal evidence). These evidence codes are from of the Gene Ontology project [28]. If the evidence code is IDA, then the property was directly observed by one of the authors or an expert mentioned in the acknowledgements.

Genome sequencing and annotation Genome project history
This organism was selected for sequencing on the basis of its phylogenetic position [29], and is part of the Genomic Encyclopedia of Bacteria and Archaea project [30]. The genome project is deposited in the Genomes On Line Database [31] and the complete genome sequence is deposited in GenBank. Sequencing, finishing and annotation were performed by the DOE Joint Genome Institute (JGI). A summary of the project information is shown in Table 2.

Genome sequencing and assembly
The genome was sequenced using a combination of Illumina and 454 sequencing platforms. All general aspects of library construction and se-quencing can be found at the JGI website [34]. Pyrosequencing reads were assembled using the Newbler assembler version 2.3-PreRelease-09-14-2009-bin (Roche). The initial Newbler assembly consisting of 100 contigs in two scaffolds was converted into a phrap assembly [35] by making fake reads from the consensus, to collect the read pairs in the 454 paired-end library. Illumina GAii sequencing data (920.8 Mb) was assembled with Velvet, version 0.7.63 [36] and the consensus sequences were shredded into 1.5 kb overlapped fake reads and assembled together with the 454 data. The 454 draft assembly was based on 109.0 Mb of 454 standard data and all of the 454 paired end data. Newbler parameters are -consed -a 50 -l 350 -g -m -ml 20. The Phred/Phrap/Consed software package [35] was used for sequence assem-bly and quality assessment in the subsequent finishing process. After the shotgun stage, reads were assembled with parallel phrap (High Performance Software, LLC). Possible mis-assemblies were corrected with gapResolution [34], Dupfinisher [37], or sequencing cloned bridging PCR fragments with subcloning or transposon bombing (Epicentre Biotechnologies, Madison, WI). Gaps between contigs were closed by editing in Consed, by PCR and by Bubble PCR primer walks (J.-F.Chang, unpublished). A total of 193 additional reactions and four shatter libraries were necessary to close gaps and to raise the quality of the finished sequence. Illumina reads were also used to correct potential base errors and increase consensus quality using a software Polisher developed at JGI [38]. The error rate of the completed genome sequence is less than 1 in 100,000.

Genome annotation
Genes were identified using Prodigal [39] as part of the Oak Ridge National Laboratory genome an-notation pipeline, followed by a round of manual curation using the JGI GenePRIMP pipeline [40]. The predicted CDSs were translated and used to search the National Center for Biotechnology Information (NCBI) nonredundant database, Uni-Prot, TIGR-Fam, Pfam, PRIAM, KEGG, COG, and In-terPro databases. Additional gene prediction analysis and functional annotation was performed within the Integrated Microbial Genomes -Expert Review (IMG-ER) platform [41].

Genome properties
The genome consists of a 4,242,803 bp long chromosome with a G+C content of 47%, as well as three plasmids of 6,277 bp, 18,280 bp and 40,303 bp length (Table 3 and Figure 3). Of the 3,838 genes predicted, 3,737 were protein-coding genes, and 101 RNAs; 96 pseudogenes were also identified. The majority of the protein-coding genes (57.3%) were assigned with a putative function while the remaining ones were annotated as hypothetical proteins. The distribution of genes into COGs functional categories is presented in Table 4.