Arginine metabolism in lactic streptococci

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Abstract
Streptococcus lactis metabolizes arginine via the arginine deiminase pathway producing ornithine, NH3, CO2 and ATP. In the 4 strains of S. lactis examined, the specific activities of arginine deiminase (EC 3.5.3.6) and ornithine transcarbamylase (EC 2.1.3.3.) were 5- to 10-fold higher in galactose-grown cells compared with glucose- or lactose-grown cells. The addition of arginine increased the specific activities of these 2 enzymes with all growth sugars. The specific activity of the 3rd enzyme involved in arginine metabolism (carbamate kinase, EC 2.7.2.2) was not altered by the composition of the growth medium. In continuous cultures arginine deiminase was not induced and arginine was not metabolized until glucose limitation occurred. In batch cultures the metabolism of glucose and arginine was sequential, whereas galactose and arginine were metabolized concurrently, and the energy derived from arginine metabolism was efficiently coupled to growth. No arginine deiminase activity was detected in the 9 S. cremoris strains examined, thus accounting for their inability to metabolize arginine. All 9 strains of S. cremoris had specific activities of carbamate kinase similar to those found in S. lactis, but only 5 S. cremoris strains had ornithine transcarbamylase activity.