Catalyzes the reversible NAD(+)-dependent oxidation of scyllo-inositol (SI) to 2,4,6/3,5-pentahydroxycyclohexanone (scyllo-inosose or SIS). Is required for SI catabolism that allows B.subtilis to utilize SI as the sole carbon source for growth. Cannot use NADP(+) instead of NAD(+). NAD(+) + scyllo-inositol = H(+) + NADH + scyllo-inosose Polyol metabolism. Induced by either myo-inositol (MI) or SI; SI is approximately three times more efficient than MI. Inactivation of this gene abolishes growth on SI as the sole carbon source, but does not affect growth on MI or glucose. Belongs to the Gfo/Idh/MocA family.