A mutant of Mycobacterium smegmatis unable to use the dipeptide carnosine (
beta-alanyl-L-histidine) as a sole carbon or nitrogen source was isolated.
Carnosinase activity and the ability to grow on beta-Ala and/or L-His were
similar in the mutant and the wild type. However, the mutant showed signifi
cant impairment in the uptake of carnosine. This study is the first descrip
tion of a peptide utilization mutant of a mycobacterium.