Strain 56-150^T (= DSM 12563 = ATCC 51284 = CIP 105832) is the type strain of the species Brachyspira murdochii. This strain was first described as Serpulina murdochii [1,2], and later transferred to the genus Brachyspira [3]. The genus Brachyspira currently consists of seven species, with Brachyspira aalborgi as the type species [4,5]. The genus Brachyspira is the only genus in the not yet formally described family ‘Brachyspiraceae’ [6,7]. The generic name derives from ‘brachys’, Greek for short, and ‘spira’, Latin for a coil, a helix, to mean ‘a short helix’ [5]. The species name for B. murdochii derives from the city of Murdoch, in recognition of work conducted at Murdoch University in Western Australia, where the type strain was identified [1]. Some species of the genus Brachyspira cause swine dysentery and porcine intestinal spirochetosis. Swine dysentery is a severe, mucohemorrhagic disease that sometimes leads to death of the animals [1]. B. murdochii is generally not considered to be a pathogen, although occasionally it has been seen in association with colitis in pigs [3,8], and was also associated with clinical problems on certain farms [9-11].

In 1992, a user-friendly and robust novel PCR-based restriction fragment length polymorphism analysis of the Brachyspiranox-gene was developed, which allows one to identify, with high specificity, members of B. murdochii using only two restriction endonucleases [12]. More recently, a multi-locus sequence typing scheme was developed that facilitates the identification of Brachyspira species and reveals the intraspecies diversity of B. murdochii [13] (see also http://pubmlst.org/brachyspira/).

Only one genome of a member of the family ‘Brachyspiraceae’ been sequenced to date: B. hyodysenteriae strain WA1 [14],. It is an intestinal pathogen of pigs. Based on 16S rRNA sequence this strain is 0.8% different from strain 56-150^T. Here we present a summary classification and a set of features for B. murdochii 56-150^T, together with the description of the complete genomic sequencing and annotation.

Brachyspira species colonize the lower intestinal tract (cecum and colons) of animals and humans [6]. The type of B. murdochii, 56-150^T, was isolated from a healthy swine in Canada [1,15]. Other isolates have been obtained from wild rats in Ohio, USA, from laboratory rats in Murdoch, Western Australia [16], and from the joint fluid of a lame pig [17]. Further isolates have been obtained from the feces or gastrointestinal tract of pigs in Canada, Tasmania, Queensland, and Western Australia [2,15]. The type strains of the other species of the genus Brachyspira share 95.9-99.4% 16S rRNA sequence identity with strain 56-150^T. GenBank contains 16S rRNA sequences for about 250 Brachyspira isolates, all of which share at least 96% sequence identity with strain 56-150^T [18]. The closest related type strain of a species outside of the Brachyspira, but within the order Spirochaetales, is Turneriella parva [19], which exhibits only 75% 16S rRNA sequence similarity [18]. 16S rRNA sequences from environmental samples and metagenomic surveys do not exceed 78-79% sequence similarity to strain 56-150^T, with the sole exception of one clone from a metagenome analysis of human diarrhea [20], indicating that members of the species, genus and even family are poorly represented in the habitats outside of various animal intestines screened thus far (status March 2010).

Figure 1 shows the phylogenetic neighborhood of B. murdochii 56-150^T in a 16S rRNA based tree. The sequence of the single 16S rRNA gene in the genome sequence is identical with the previously published 16S rRNA gene sequence generated from DSM 12563 (AY312492).

Figure 1 Phylogenetic tree highlighting the position of B. murdochii 56-150T relative to the other type strains within the genus and to the type strains of the other genera within the class Spirochaetes (excluding members of the Spirochaetaceae). The tree was inferred from 1,396 aligned characters [21,22] of the 16S rRNA gene sequence under the maximum likelihood criterion [23] and rooted in accordance with the current taxonomy. The branches are scaled in terms of the expected number of substitutions per site. Numbers above branches are support values from 1,000 bootstrap replicates if [24] larger than 60%. Lineages with type strain genome sequencing projects registered in GOLD [25] are shown in blue, published genomes in bold.

The cells of B. murdochii 56-l50^T were 5 - 8 by 0.35 - 0.4 µm in size (Table 1 and Figure 2), and each cell possessed 22 to 26 flagella (11 to 13 inserted at each end) [1]. In brain/heart infusion broth containing 10% calf serum (BHIS) under an N₂-O₂ (99::l) atmosphere, strain 56-150^T had optimum growth temperatures of 39 to 42°C (shortest population doubling times and highest final population densities) [1]. In BHIS broth at 39°C, the doubling times of strain 56-150^T were 2 to 4 h, and the final population densities were 0.5 x l0⁹ to 2.0 x l0⁹ cells/ml. Strain 56-150^T did not grow at 32 or 47°C [1].

Figure 2 Scanning electron micrograph of B. murdochii 56-150T

Substrates that support growth of strain 56-150^T in HS broth (basal heart infusion broth containing 10% fetal calf serum) include glucose, fructose, sucrose, N-acetylglucosamine, pyruvate, L-fucose, cellobiose, trehalose, maltose, mannose, and lactose, but not galactose, D-fucose, glucosamine, ribose, raffinose, rhamnose, or xylose [1]. In HS broth supplemented with 0.4% glucose under an N₂-O₂ (99:l) atmosphere, the metabolic end products of strain 56-150^T are acetate, butyrate, ethanol, CO₂, and H₂. Strain 56-150^T produces more H₂ than CO₂ [1], which is indicative of NADH-ferredoxin oxidoreductase reaction [6]. The ethanol is likely to be formed from acetyl-CoA by the enzymes acetaldehyde dehydrogenase and alcohol dehydrogenase [6]. Strain 56-150^T is weakly hemolytic, negative for indole production, does not hydrolyze hippurate, is negative for α-galactosidase and α-glucosidase activity, but positive for β-glucosidase activity [1]. Strain 56-150^T is anaerobic but aerotolerant [1].

Minimal inhibitory concentrations have been determined for strain 56-150^T for tiamulin hydrogen fumarate, tylosin tartrate, erythromycin, clindamycin hydrochloride, virginiamycin, and carbadox [36]. Several strains of B. murdochii have been described to be naturally resistant against the rifampicin [7,32]. Also, a ring test for quality assessment for diagnostics and antimicrobial susceptibility testing of the genus Brachyspira has been reported [37].

The genome is 3,241,804 bp long and comprises one main circular chromosome with an overall GC content of 27.8% (Table 3 and Figure 3). Of the 2,893 genes predicted, 2,853 were protein-coding genes, and 40 RNAs. A total of 44 pseudogenes were identified. The majority of the protein-coding genes (66.2%) were assigned a putative function while those remaining were annotated as hypothetical proteins. The distribution of genes into COGs functional categories is presented in Table 4.

Figure 3 Graphical circular map of the genome. From outside to the center: Genes on forward strand (color by COG categories), Genes on reverse strand (color by COG categories), RNA genes (tRNAs green, rRNAs red, other RNAs black), GC content, GC skew.