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.