Propionispora vibrioides, nov. gen., nov. sp., a new gram-negative, spore-forming anaerobe that ferments sugar alcohols

Anaerobic enrichment cultures, with erythritol as substrate, resulted in the isolation of a strain with properties not yet found in an existing genus in this combination. The strain, FKBS1, was strictly anaerobic, stained gram-negative and formed spores. Cells were small motile vibrios with flagella inserted at the concave side of the cell. Spores were located terminally and caused only slight swelling of the cells if compared to related spore-forming genera. FKBS1 fermented fructose, mannitol, sorbitol, xylitol and erythritol to propionic acid, acetic acid, CO2 and small amounts of H2 to balance the difference in the oxidation-reduction value between substrate and cell mass. The 16S rDNA sequence revealed relationship to the Sporomusa-Pectinatus-Selenomonas group. However, the phylogenetic distance to any of its members was too great to allow it to be placed in one of the existing genera. Morphologically the strain resembled Sporomusa, which, however, performs an acetogenic type of fermentation. The propionic-acid-forming genera of the group are either not spore-formers or, in the case of Dendrosporobacter quercicolus (syn. Clostridium quercicolum), morphologically different. It is therefore proposed to classify strain FKBS1 as a new genus and species, Propionispora vibrioides.