Lactose and Maltose Uptake by Streptococcus lactis

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Abstract
Resting cells of S. lactis 7962 were examined for rate of uptake of radioactive lactose following growth of the cells in broth media containing lactose, maltose, glucose, or glucose plus lactose as C sources. Lactose-grown cells accumulated label at the fastest rate, followed in order by cells grown on maltose, lactose plus glucose, or glucose. The uptake of radioactive maltose and methyl-B-D-thio-galactopyranoside (TMG) was also examined following growth of the cells in broth containing maltose or lactose. Labeled TMG was not taken up at an appreciable rate, especially by the maltose-grown cells; radioactive maltose, was accumulated rapidly by maltose-grown cells but only at a very low rate by lactose-grown cells. These data indicated that specific permeases and/or metabolic enzymes were induced by lactose and maltose in S. lactis 7962. Inhibition of substrate uptake by glucose indicated that synthesis of these enzyme systems was controlled by catabolite repression.

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