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Spirochaeta cellobiosiphila sp. nov., a facultatively anaerobic, marine spirochaete

John A. Breznak^1, and Falk Warnecke²

¹ Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824-4320, USA
² Microbial Ecology Program, DOE Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA

Correspondence
John A. Breznak
breznak{at}msu.edu

A facultatively anaerobic, marine spirochaete, designated strain SIP1^T, was isolated from interstitial water from a cyanobacteria-containing microbial mat. Cells of strain SIP1^T were 0.3–0.4x10–12 µm in size, helical with a body pitch of approximately 1.4 µm and motile by means of two to four periplasmic flagella (one, or occasionally two, being inserted near each end of the cell). Cells were catalase-negative and used a variety of monosaccharides and disaccharides and pectin as energy sources, growing especially well on cellobiose. Neither organic acids nor amino acids were utilized as energy sources. One or more amino acids in tryptone and one or more components of yeast extract were required for growth. Growth was observed at 9–37 °C (optimally at or near 37 °C), at initial pH 5–8 (optimally at initial pH 7.5) and in media prepared with 20–100 % (v/v) seawater (optimally at 60–80 %) or 0.10–1.00 M NaCl (optimally at 0.30–0.40 M). The products of cellobiose fermentation were acetate, ethanol, CO₂, H₂ and small amounts of formate. Aerated cultures performed incomplete oxidation of cellobiose to acetate (and, presumably, CO₂) plus small amounts of ethanol and formate, but exhibited a Y_cellobiose that was only slightly greater than that of cellobiose-fermenting anoxic cultures. The G+C content of the genomic DNA of strain SIP1^T was 41.4 mol%, the lowest among known spirochaetas. On the basis of its 16S rRNA gene sequence, strain SIP1^T was grouped among other members of the genus Spirochaeta, but it bore only 89 % similarity with respect to its closest known relatives, Spirochaeta litoralis and Spirochaeta isovalerica, two marine obligate anaerobes. On the basis of its phenotypic properties and phylogenetic position, strain SIP1^T represents a novel species of the genus Spirochaeta, for which the name Spirochaeta cellobiosiphila sp. nov. is proposed. The type strain is SIP1^T (=ATCC BAA-1285^T =DSM 17781^T).

The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain SIP1^T is EU448140.

Details of the dataset used for the construction of the maximum-likelihood phylogenetic tree based on 16S rRNA gene sequences are available as supplementary material with the online version of this paper.