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We describe the main characteristics of Christensenella massiliensis, strain Marseille-P2438T (CSUR P2438), isolated from a stool specimen of a 66-year-old patient.
Here we present an early description of a new bacterium isolated as part of culturomics study of the human gut microbiota  from the stool specimen of a 66-year-old patient hospitalized in November 2015 at the Timone Hospital in Marseilles, France. Approval of the study by the local ethics committee of IFR48 (Marseille, France) was obtained beforehand under agreement 09-022. After obtaining the consent signed by the patient, the stool sample was directly preincubated for 7 days in an anaerobic blood bottle culture supplemented with 5 mL of rumen fluid. Then isolated colonies of the strain were obtained by subculturing on 5% sheep's blood agar (bioMérieux, Marcy l'Etoile, France) in anaerobic conditions generated by AnaeroGen (bioMérieux) after 4-day incubation. Our systematic matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) screening on a MicroFlex spectrometer (Bruker Daltonics, Leipzig, Germany)  was unable to identify this strain.
The strain Marseille-P2438 features Gram-negative bacilli which was strict anaerobic, nonmotile and non–spore forming (0.3–0.5 × 1.2–1.5 μm). It presents no catalase and oxidase activity. The colonies are yellow-white, circular and about 0.1 to 0.2 mm in diameter after 4-day incubation on 5% sheep's blood agar. Optimal growth occurs at 37°C, pH 7 and 0.5% NaCl. Using a 3130-XL sequencer (Applied Biosciences, Saint Aubin, France), the 16S rRNA gene was sequenced using the universal primers fD1 and rp2 (Eurogentec, Angers, France), as previously described . Strain Marseille-P2438 (GenBank accession no. LT161898) exhibited a 97.5% sequence identity with Christensenella minuta strain YIT 12065T (GenBank accession no. NR112900), the phylogenetically closest species with standing in nomenclature (Fig. 1), which putatively classifies it as a member within the genus Christensenella in the Firmicutes phylum .
C. minuta strain YIT 12065TT is strictly anaerobic, Gram-negative, nonmotile and non–spore forming, and are short, straight rods isolated from human faeces. Catalase and oxidase activities for C. minuta were negative. To date, it is the first species of Christensenella genus published with a validated name .
Strain Marseille-P2438 shows a 16S rRNA gene sequence divergence of >1.3% with its phylogenetically closest species with a validly published name with standing in nomenclature . On the basis of these results, strain Marseille-P2438T is proposed as a novel species within the genus Christensenella, namely Christensenella massiliensis sp. nov.
The MALDI-TOF MS spectrum of Christensenella massiliensis is available online (http://www.mediterraneeinfection.com/article.php?laref=256&titre=urms-database).
The 16S rRNA gene sequence was deposited in GenBank under accession number LT161898.
Strain Marseille-P2438T was deposited in the Collection de Souches de l'Unité des Rickettsies (CSUR) under number P2438.
This study was funded by the Fondation Méditerranée Infection.