An indigo-reducing moderate thermophile from a woad vat, Clostridium isatidis sp. nov.

A Gram-positive, anaerobic, moderate thermophile, strain Wv6T, capable of reducing indigo dye, was isolated from a fermenting woad vat prepared essentially as in medieval Europe. Strain Wv6T formed rod-shaped cells, which occurred singly, in pairs or in chains and produced terminal oval endospores. Strain Wv6T was saccharolytic. Growth occurred at pH 5.9-9.9 (initial pH) with an optimum at 50 degrees C of pH 7.2 +/- 0.2 (constant pH). At pH 7.8, the temperature range for growth was 30-55 degrees C with the optimum at 49-52 degrees C. Comparative 16S rRNA gene sequence analysis demonstrated that the bacterium represents a hitherto unknown subline within rRNA cluster I Clostridium. Based on the results of the phylogenetic analysis and phenotypic criteria, it is proposed that the unknown moderate thermophile should be classified as Clostridium isatidis sp. nov., a new species of the genus Clostridium. The type strain of Clostridium isatidis is strain Wv6T (= NCFB 3071T).