Distinct galactose phosphoenolpyruvate-dependent phosphotransferase system in Streptococcus lactis

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Genetics

Background:

• Streptococcus lactis C2 is a bacterium relevant to dairy fermentation.
• Lactose metabolism in bacteria is often mediated by plasmids.
• Understanding sugar transport systems is crucial for microbial physiology.

Purpose of the Study:

• To investigate the galactose metabolism of lactose-negative (Lac-) mutants of Streptococcus lactis.
• To determine if galactose transport is linked to the lactose phosphotransferase system.
• To identify the genetic basis for galactose utilization in S. lactis.

Main Methods:

• Isolation and characterization of Lac- mutants from a strain with integrated lactose plasmid.
• Growth analysis on galactose media.
• Measurement of [14C]thiomethyl-beta-D-galactopyranoside accumulation.
• Analysis of galactose phosphorylation products.

Main Results:

• Lac- Gal+ mutants, unlike Lac- variants with lost lactose plasmid, maintained parental growth on galactose.
• Mutants showed defects in lactose phosphotransferase system activity but retained galactose phosphorylation.
• Evidence suggests a separate galactose phosphotransferase system encoded on the lactose plasmid.

Conclusions:

• Galactose transport in S. lactis is not mediated by the lactose phosphotransferase system.
• A distinct galactose phosphotransferase system exists and is likely encoded on the lactose plasmid.
• The lactose plasmid carries genetic loci for both lactose and galactose transport systems.