Subpopulation behaviors in lactose metabolism by Streptococcus mutans.

Area of Science:

• Microbiology
• Molecular Biology
• Oral Health

Background:

• Streptococcus mutans growth on lactose is delayed, with glucose release.
• Stochastic gene expression, or bet-hedging, is observed in bacterial populations.
• Understanding lac operon regulation is key to S. mutans's metabolic flexibility.

Purpose of the Study:

• To investigate stochastic transcription of the lac operon in S. mutans.
• To determine the role of carbohydrate source and strain on lac operon induction.
• To explore the implications of metabolic bet-hedging and cheating on oral biofilm dynamics.

Main Methods:

• Utilized gfp reporter fusions to monitor lac operon expression in S. mutans strains UA159 and GS-5.
• Assessed glucokinase activity and glucose release under different carbohydrate conditions.
• Employed engineered obligate cheating and non-cheating strains to study population dynamics.
• Evaluated strain competitiveness in a human-derived consortium biofilm model.

Main Results:

• Lac operon induction occurred in a sub-population, influenced by prior carbohydrate exposure and strain.
• Lower glucokinase activity in strain GS-5 correlated with higher glucose release and lower lac expression.
• Lactose-non-utilizing mutants grew in co-culture with lactose-utilizing strains, indicating cheating.
• Engineered cheaters sustained heterogeneous populations and demonstrated competitive fitness in biofilms.

Conclusions:

• Bet-hedging in carbohydrate metabolism influences S. mutans population structure.
• Cheating behavior can sustain metabolic heterogeneity within oral biofilms.
• These metabolic strategies may significantly impact the pathogenic potential of oral biofilms.