A bacterium, strain SKN, that was able to utilize saccharin as the sole source of carbon and energy for aerobic growth, was enriched and isolated from communal sewage. The isolate was identified as a strain of Sphingomonas xenophaga. Saccharin was quantitatively converted to cell material, sulfate, ammonium and, presumably, CO(2). The specific rate of saccharin-dependent oxygen uptake during growth reached a maximum before the culture entered the stationary phase and then fell to undetectable levels. Saccharin was degraded only in the presence of molecular oxygen. Catechol was detected as an intermediate during degradation of saccharin in whole cells and catechol 1,2-dioxygenase was expressed inducibly during growth with saccharin. There was an apparent requirement of 2 mol O(2)/mol saccharin to remove the substituents on the ring and to cleave the ring. We presume that S. xenophaga SKN synthesizes a multi-component saccharin dioxygenase that simultaneously cleaves off both vicinal substituents from the aromatic ring to yield catechol and the undefined precursor of CO(2) as well as sulfate and ammonium ions.