Galactose Transport in Streptococcus thermophilus

Authors

Robert W. Hutkins, University of Nebraska-LincolnFollow
Howard A. Morris, University of Minnesota, St. Paul, Minnesota
Larry L. McKay, University of Minnesota, St. Paul, Minnesota

Document Type

Article

Date of this Version

October 1985

Comments

Published in APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Oct. 1985, p. 772-776. Copyright 1985, American Society for Microbiology. Used by permission.

Abstract

Although Streptococcus thermophilus accumulated [¹⁴C]lactose in the absence of an endogenous energy source, galactose-fermenting (Gal⁺) cells were unable to accumulate [¹⁴C]galactose unless an additional energy source was added to the test system. Both Gal⁺ and galactose-nonfermenting (Gal^-) strains transported galactose when preincubated with sucrose. Accumulation was inhibited 50 or 95% when 10 niM sodium fluoride or 1.0 mM iodoacetic acid, respectively, was added to sucrose-treated cells, indicating that ATP was required for galactose transport activity. Proton-conducting ionophores also inhibited galactose uptake, although N,N'-dicyclohexyl carbodiimide had no effect. The results suggest that galactose transport in S. thermophilus occurs via an ATP-dependent galactose permease and that a proton motive force is involved. The galactose permease in S. thermophilus TS2b (Gal⁺) had a K_m for galactose of 0.25 mM and a V_max of 195 μmol of galactose accumulated per min per g (dry weight) of cells. Several structurally similar sugars inhibited galactose uptake, indicating that the galactose permease had high affinities for these sugars.