scyllo-Inositol (SI) is a stereoisomer of inositol whose catabolism has not been characterized in bacteria. We found thatBacillus subtilis168 was able to grow using SI as its sole carbon source and that this growth was dependent on a functionalioloperon for catabolism ofmyo-inositol (MI; another inositol isomer, which is abundant in nature). Previous studies elucidated the MI catabolic pathway inB. subtilisas comprising multiple stepwise reactions catalysed by a series of Iol enzymes. The first step of the pathway converts MI toscyllo-inosose (SIS) and involves the MI dehydrogenase IolG. Since IolG does not act on SI, we suspected that there could be another enzyme converting SI into SIS, namely an SI dehydrogenase. Within the whole genome, seven genes paralogous toiolGhave been identified and two of these,iolXandiolW(formerly known asyisSandyvaA, respectively), were selected as candidate genes for the putative SI dehydrogenase since they were both prominently expressed whenB. subtiliswas grown on medium containing SI.iolXandiolWwere cloned inEscherichia coliand both were shown to encode a functional enzyme, revealing the two distinct SI dehydrogenases inB. subtilis. Since inactivation ofiolXimpaired growth with SI as the carbon source, IolX was identified as a catabolic enzyme required for SI catabolism and it was shown to be NAD+dependent. The physiological role of IolW remains unclear, but it may be capable of producing SI from SIS with NADPH oxidation.