Complete genome sequence of the aquatic bacterium Runella slithyformis type strain (LSU 4T)

Runella slithyformis Larkin and Williams 1978 is the type species of the genus Runella, which belongs to the Cytophagaceae, a family that was only recently classified to the order Cytophagales in the class Cytophagia. The species is of interest because it is able to grow at temperatures as low as 4°C. This is the first completed genome sequence of a member of the genus Runella and the sixth sequence from the family Cytophagaceae. The 6,919,729 bp long genome consists of a 6.6 Mbp circular genome and five circular plasmids of 38.8 to 107.0 kbp length, harboring a total of 5,974 protein-coding and 51 RNA genes and is a part of the Genomic Encyclopedia of Bacteria and Archaea project.


Introduction
Strain LSU 4 T (= DSM 19594 = ATCC 29530 = NCIMB 11436) is the type strain of the species Runella slithyformis, which is the type species of its genus Runella [1,2]. The genus currently consists of four validly named species [3]. The genus name is derived from 'rune', a runic letter and the Latin diminutive ending 'ella', yielding the Neo-Latin word 'Runella', meaning 'that which resembles figures of the runic alphabet' [3]. The species epithet is derived from slithy, a nonsense word from Lewis Carroll's Jabberwocky for a fictional organism that is 'slithy' and the Latin word 'suffix' meaning '-like, in the shape of', yielding the Neo-Latin word 'slithyformis' meaning 'slithy in form' [3]. R. slithyformis strain LSU 4 T was isolated from University Lake near Baton Rouge, Louisiana, USA, and described by Larkin and Williams in 1978 [1]. Another strain of R. slithyformis, termed strain 6, was isolated from Elbow Bayou near Baton Rouge [1]. Members of the genus Runella colonize diverse environmental habitats, preferentially aquatic ecosystems, including water bodies in Baton Rouge [1], a wastewater treatment plant in South-Korea [4], environmental water samples and their biofilms in Standards in Genomic Sciences Japan [5], and an activated sludge process involved in enhanced biological removal of phosphor in Korea [6]. Another species of this genus was also isolated from the stems of surface-sterilized maize [7]. Here we present a summary classification and a set of features for R. slithyformis strain LSU 4 T , together with the description of the complete finished genome sequencing and annotation.

Classification and features
A representative genomic 16S rRNA sequence of R. slithyformis LSU 4 T was compared using NCBI BLAST [8,9] under default settings (e.g., considering only the high-scoring segment pairs (HSPs) from the best 250 hits) with the most recent release of the Greengenes database [10] and the relative frequencies of taxa and keywords (reduced to their stem [11]) were determined, weighted by BLAST scores. The most frequently occurring genera were Runella (31.0%), Dyadobacter (30.3%), Cytophaga (13.7%), Cyclobacterium (7.5%) and Algoriphagus (4.0%) (51 hits in total). Regarding the single hit to sequences from members of the species, the average identity within HSPs was 99.2%, whereas the average coverage by HSPs was 96.9%. Regarding the two hits to sequences from other members of the genus, the average identity within HSPs was 95.0%, whereas the average coverage by HSPs was 91.1%. Among all other species, the one yielding the highest score was R. zeae (NR_025004), which corresponded to an identity of 95.0% and an HSP coverage of 91.1%. (Note that the Greengenes database uses the INSDC (= EMBL/NCBI/DDBJ) annotation, which is not an authoritative source for nomenclature or classification.) The highest-scoring environmental sequence was GQ480089 ('changes during sewage treated process activated sludge wastewater treatment plant clone BXHB50'), which showed an identity of 96.6% and an HSP coverage of 98.0%. The most frequently occurring keywords within the labels of all environmental samples which yielded hits were 'skin' (5.5%), 'soil' (2.1%), 'sludg' (2.0%), 'biofilm' (1.7%) and 'forearm, volar' (1.7%) (199 hits in total). While few of these keywords fit the aquatic and sludge environments from which strain LSU 4 T originated, the majority of the hits point to human and even soil, which were, until now, not considered as habitats for R. slithyformis. However, environmental samples which yielded hits of a higher score than the highest scoring species were not found. Figure 1 shows the phylogenetic neighborhood of R. slithyformis LSU 4 T in a 16S rRNA based tree. The sequences of the two identical 16S rRNA gene copies in the genome do not differ from the previously published 16S rRNA sequence (M62786), which contains 13 ambiguous base calls. The cells of strain LSU 4 T are generally curved rods, with the degree of curvature of individual cells within a culture varying from nearly straight to crescent shape. Cell diameter varies from 0.5 to 0.9 µm, and the length from 2.0 to 3.0 µm [1]. With its curved rod shape, strain LSU 4 T differs from other members of the genus, such as R. limosa which has long rods while R. zeae is bent rodshaped [6]. On the MS agar medium used at the time of isolation, R. slithyformis rarely formed long spirals. However, Chelius and Triplett [23] reported the formation of long spirals by the strain LSU 4 T when cells were allowed to grow in R2A broth medium (see Figure 2). Larkin and Williams [1] reported a possible production of filaments up to 14 µm in length, which are not coiled. This contrasts the findings of Chelius et al. [7] who described the cells of the strain LSU 4 T as circular with swollen ends that would not form filaments. Rings with an outer diameter of 2.0 to 3.0 µm may also occur [1]. Colonies produced a pale pink, nondiffusible, nonfluorescent pigment on MS agar [1]. The strain LSU 4 T is a Gram-negative bacterium (Table 1). Strain LSU 4 T is non-motile, aerobic and chemoorganotrophic [1]. It does not grow on media with NaCl concentrations of 1.5% or higher [23]. This feature was similar to that of another member of this genus, R. zeae [7]. The temperature range for growth is between 4°C-37°C, with an optimum between 20°C-30°C [6]; the strain being unable to grow at temperatures above 37°C [23]. The sole carbon sources used by the strain LSU 4 T for growth on MS agar are glycogen, D-arabitol, dulcitol, inositol, mannitol, sorbitol and sorbose, but the growth was weak except in the presence of glycogen [23]. Some of these features are however contradictory to the findings of Chelius et al. [7] whose attempt to grow the strain LSU 4 T in the presence of glycogen in R2A medium was unsuccessful. Further detailed physiological insight, e.g., carbon source utilization in R2A medium, MS agar medium, or by the API 50 CH test, have been reported previously [7,23]. Also, resistance to a variety of antibiotics has been reported [7,23].

Figure 1.
Phylogenetic tree highlighting the position of R. slithyformis relative to the type strains of the type species of the other genera within the family Cytophagaceae. The tree was inferred from 1,330 aligned characters [12,13] of the 16S rRNA gene sequence under the maximum likelihood (ML) criterion [14]. Rooting was done initially using the midpoint method [15] and then checked for its agreement with the current classification ( Table 1). The branches are scaled in terms of the expected number of substitutions per site. Numbers adjacent to the branches are support values from 400 ML bootstrap replicates [16] (left) and from 1,000 maximum parsimony bootstrap replicates [17] (right) if larger than 60%. Lineages with type strain genome sequencing projects registered in GOLD [18] are labeled with one asterisk, those also listed as 'Complete and Published' with two asterisks [19][20][21][22].

Genome sequencing and annotation Genome project history
This organism was selected for sequencing on the basis of its phylogenetic position [34], and is part of the Genomic Encyclopedia of Bacteria and Archaea project [35]. The genome project is deposited in the Genomes On Line Database [18] 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 sequencing can be found at the JGI website [37]. Pyrosequencing reads were assembled using the Newbler assembler (Roche). The initial Newbler assembly consisting of 121 contigs in two scaffolds was converted into a phrap [38] assembly by making fake reads from the consensus, to collect the read pairs in the 454 paired end library. Illumina GAii sequencing data (638.9 Mb) was assembled with Velvet [39] and the consensus sequences were shredded into 2.0 kb overlapped fake reads and assembled together with the 454 data. The 454 draft assembly was based on 206.2 Mb 454 draft 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 [38] was used for sequence assembly 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 [37], Dupfinisher [40], or sequencing cloned bridging PCR fragments with subcloning. Gaps between contigs were closed by editing in Consed, by PCR and by Bubble PCR primer walks (J.-F. Chang, unpublished). A total of 289 additional reactions and 3 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 [41]. The error rate of the completed genome sequence is less than 1 in 100,000. Together, the combination of the Illumina and 454 sequencing platforms provided 128.6 × coverage of the genome. The final assembly contained 540,807 pyrosequence and 19,068,176 Illumina reads.

Genome annotation
Genes were identified using Prodigal [42] as part of the Oak Ridge National Laboratory genome annotation pipeline, followed by a round of manual curation using the JGI GenePRIMP pipeline [43]. The predicted CDSs were translated and used to search the National Center for Biotechnology Information (NCBI) nonredundant database, UniProt, TIGR-Fam, Pfam, PRIAM, KEGG, COG, and InterPro databases. Additional gene prediction analysis and functional annotation was performed within the Integrated Microbial Genomes -Expert Review (IMG-ER) platform [44].

Genome properties
The genome consists of one circular chromosome with a length of 6,568,739 bp and a G+C content of 47%, and five circular plasmids with 38,784 bp, 44,754 bp, 66,926 bp, 93,527 bp and 106,999 bp length, respectively (Table 3 and Figure 3). Of the 6,025 genes predicted, 5,974 were protein-coding genes, and 51 RNAs; 182 pseudogenes were also identified. The majority of the protein-coding genes (59.7%) were assigned 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.