The sulfur of taurine can be assimilated by Klebsiella sp. during aerobic growth, but not fermentative growth. However, taurine's N can be utilized by this bacterium as sole nitrogen source for both aerobic and anaerobic growth. Two other amino-containing sulfonates (3-aminopropanesulfonate and cysteate) were also examined for their abilities to serve as nitrogen sources for Klebsiella sp. during the different growth conditions. The result shows that 3-aminopropanesulfonate only supports aerobic growth while cysteate does not under either condition.