Classification and features
A representative genomic 16S rRNA sequence of strain 1651/6T was compared using NCBI BLAST 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 [9] and the relative frequencies of taxa and keywords (reduced to their stem [10]) were determined, weighted by BLAST scores. The most frequently occurring genera were Bacteroides (43.5%), Odoribacter (37.9%), Alistipes (15.2%) and Brumimicrobium (3.4%) (21 hits in total). Regarding the two hits to sequences from members of the species, the average identity within HSPs was 99.7%, whereas the average coverage by HSPs was 97.9%. Regarding the two hits to sequences from other members of the genus, the average identity within HSPs was 93.4%, whereas the average coverage by HSPs was 42.5%. The highest-scoring environmental sequence was EF401000 ('human fecal clone SJTU D 04 48'), which showed an identity of 99.8% and an HSP coverage of 98.2%. The most frequently occurring keywords within the labels of environmental samples which yielded hits were 'human' (13.4%), 'biopsi' (7.4%), 'mucos' (7.1%), 'fecal' (6.1%) and 'colon' (5.3%) (229 hits in total). The most frequently occurring keyword within the labels of environmental samples which yielded hits of a higher score than the highest scoring species was 'fecal/human' (50.0%) (27 hits in total).
Figure 1 shows the phylogenetic neighborhood of O. splanchnicus in a 16S rRNA based tree. The sequences of the four 16S rRNA gene copies in the genome differ from each other by up to eight nucleotides, and differ by up to nine nucleotides from the previously published 16S rRNA sequence (L16496), which contains nine ambiguous base calls
Figure 1  Phylogenetic tree highlighting the position of O. splanchnicus relative to the other type strains within the family Porphyromonadaceae. The tree was inferred from 1,401 aligned characters [11,12] of the 16S rRNA gene sequence under the maximum likelihood criterion [13]. Rooting was done initially using the midpoint method [14] 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 to the right of bifurcations are support values from 250 bootstrap replicates [15] if larger than 60%. Lineages with type strain genome sequencing projects registered in GOLD [16] are labeled by one asterisk, published genomes by two asterisks [17-19].   The cells of O. splanchnicus generally have the shape of short rods (0.7 × 1.0-5.0 µm) which occur singly or in lightly associated groups (Figure 2). They can also be pleomorphic. O. splanchnicus is a Gram-negative, non-pigmented and non spore-forming bacterium (Table 1). The organism is described as non-motile and only ten genes associated with motility have been found in the genome (see below). O. splanchnicus grows well at 37°C, is strictly anaerobic, chemoorganotrophic and is able to ferment glucose, fructose, galactose, arabinose, lactose and mannose but does not utilize sucrose, rhamnose, trehalose or salicin [4,5]. The organism does not reduce nitrate but it produces indole from tryptophan and hydrolyzes esculin [28]. O. splanchnicus does not require hemin for growth but is highly stimulated by its presence and does not show hemolysis on blood agar. Growth is enhanced by the addition of 20% bile. Major fermentation products are acetic acid, propionic acid and succinic acid; butyric acid, isovaleric acid and isobutyric acid are produced in small amounts [4,29]. When amino acids are used as carbon sources, only lysine enables butyrate production [4]. It is known that O. splanchnicus possesses highly active pentose phosphate pathway enzymes such as glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase as well as active malate dehydrogenase and glutamate dehydrogenase [30]. The organism produces large amounts of hydrogen and H2S. Strain 1651/6T is phosphatase, α- and β-galactosidase, α-fucosidase, N-acetylglucosaminidase and glutamic acid decarboxylase active and urease and catalase inactive [2]. The organism produces arginine arylamidase, leucyl glycine arylamidase, leucine arylamidase, alanine arylamidase (own, unpublished data) and glycylprolyl arylamidase [31]. O. splanchnicus is reported to grow in the presence of aminoglycosides and polymyxins (minimum inhibitory concentration (MIC) value greater than 60 µg/ml); chloramphenicol, penicillins and cephalosporins show bacteriostatic activity (5-40 µg/ml). The organism is susceptible to tetracyclines, lincomycin, clindamycin, rifampicin and erythromycin (MIC values less than 0.5 µg/ml) [4,28].
Figure 2  Scanning electron micrograph of O. splanchnicus 1651/6T
Table 1  Classification and general features of O. splanchnicus 1651/6T according to the MIGS recommendations [20].  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 [27]. If the evidence code is IDA, then the property was directly observed by one of the authors or an expert mentioned in the acknowledgements.

Chemotaxonomy
Little chemotaxonomic information is available for strain 1651/6T. It possesses meso-diaminopimelic acid in its peptidoglycan [30], sphingophospholipids as polar lipids [32] and the sole menaquinone present is MK-9 [30]. The major fatty acids found are iso-C15:0, C14:0, anteiso-C15:0 and C16:03-OH [30].