Streptococcus mutans serotype c tagatose 6-phosphate pathway gene cluster

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Streptococcus mutans is a key bacterium in dental caries.
• Understanding its metabolic pathways, like galactose utilization, is important for controlling its growth and virulence.
• The tagatose 6-phosphate pathway is a known route for galactose metabolism in some bacteria.

Purpose of the Study:

• To clone and characterize the genes responsible for galactose utilization in Streptococcus mutans serotype c.
• To determine the enzymatic activities, gene order, and protein sizes involved in the tagatose 6-phosphate pathway.

Main Methods:

• Cloning of DNA from Streptococcus mutans into Escherichia coli K-12.
• Analysis of protein expression in recombinant plasmids using minicells.
• Gene mapping and ordering using transposon Tn5 mutagenesis.

Main Results:

• Three enzyme activities for the tagatose 6-phosphate pathway were identified: galactose 6-phosphate isomerase, tagatose 6-phosphate kinase, and tagatose-1,6-bisphosphate aldolase.
• The genes were localized to a 3.28-kb HindIII DNA fragment.
• The molecular weights of the subunits/proteins were determined: 14- and 19-kDa for isomerase, 34-kDa for kinase, and 36-kDa for aldolase.

Conclusions:

• The cloned DNA fragment from Streptococcus mutans contains the complete genetic information for the tagatose 6-phosphate pathway.
• The characterized enzymes and their sizes are consistent with those found in other bacterial species like Staphylococcus aureus and Lactococcus lactis.
• This study provides a molecular basis for understanding galactose metabolism in Streptococcus mutans.