The Corynebacterium glutamicum aecD gene encodes a C-S lyase with a,b-elimination activity that degrades aminoethylcysteine

S-(4-Aminoethyl)-cysteine (AEC) resistance was achieved in Corynebacterium gLtamicum by cloning a chromosomal 1.5-kb EcoRV-BglI DNA ent on a multicopy plasmid. DNA sequence analysis of the 1.5-kb DNA fragment revealed an open reading frme (ORF32,) which represents the AEC resistance gene, designated aecD. The aecD gene directs the synthesis of a 36-kDa protein which was visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The aecD gene is a nonessential gene and mediates AEC resistance only in an amplified state. C. guamicum strains harboring an amplified aecD gene can utiUle AEC as an alternative nitrogen source, indicating that the AEC resistance mechanism is due to AEC degradation. Since the AEC degradation products analyzed by high-pressure liquid chromatography were found to be pyruvate and aminoethanethiol (cysteamine), it was concluded that the aecD gene encodes a C-S lyase with a,-elimination activity. Besides AEC, the C-S lyase was also able to use cysteine, cystine, and cystathionine as substrates. The gram-positive, nonpathogenic coryneform bacteria are microorganisms of industrial importance, since several members of this group, such as Brevibacterium flavum, Brevibactenum lactofermentum, and Corynebacterium glu