Lactose uptake driven by galactose efflux in Streptococcus thermophilus: Evidence for a galactose-lactose antiporter

Journal Article · Mon Apr 01 00:00:00 EST 1991 · Applied and Environmental Microbiology; (United States)

OSTI ID:5714107

Hutkins, R W; Ponne, C ^[1]

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1. Univ. of Nebraska, Lincoln (United States)

Galactose-nonfermenting (Gal{sup {minus}}) Streptococcus thermophilus TS2 releases galactose into the extracellular medium when grown in medium containing excess lactose. Starved and de-energized Gal{sup {minus}} cells, however, could be loaded with galactose to levels approximately equal to the extracellular concentration (0 to 50 mM). When loaded cells were separated from the medium and resuspended in fresh broth containing 5 mM lactose, galactose efflux occurred. De-energized, galactose-loaded cells, resuspended in buffer or medium, accumulated ({sup 14}C)lactose at a greater rate and to significantly higher intracellular concentrations than unloaded cells. Uptake of lactose by loaded cells was inhibited more than that by unloaded cells in the presence of extracellular galactose, indicating that a galactose gradient was involved in the exchange system. When de-energized, galactose-loaded cells were resuspended in carbohydrate-free medium at pH 6.7, a proton motive force ({Delta}p) of 86 to 90 mV was formed, whereas de-energized, nonloaded cells maintained a {Delta}p of about 56 mV. However, uptake of lactose by loaded cells occurred when the proton motive force was abolished by the addition of an uncoupler or in the presence of a proton-translocating ATPase inhibitor. These results support the hypothesis that galactose efflux in Gal{sup {minus}} S. thermophilus is electrogenic and that the exchange reaction (lactose uptake and galactose efflux) probably occurs via an antiporter system.

• OSTI ID: 5714107
• Journal Information: Applied and Environmental Microbiology; (United States), Vol. 57:4; ISSN 0099-2240
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
LACTOSE
METABOLISM
STREPTOCOCCUS
BIOCHEMICAL REACTION KINETICS
CARBON 14 COMPOUNDS
HYDROLYSIS
TRACER TECHNIQUES
BACTERIA
CARBOHYDRATES
CARBON COMPOUNDS
CHEMICAL REACTIONS
DECOMPOSITION
DISACCHARIDES
ISOTOPE APPLICATIONS
KINETICS
LABELLED COMPOUNDS
LYSIS
MICROORGANISMS
OLIGOSACCHARIDES
ORGANIC COMPOUNDS
REACTION KINETICS
SACCHARIDES
SOLVOLYSIS
550501* - Metabolism- Tracer Techniques