Objectives: Growth Advantage in Stationary Phase (GASP) phenotype was first reported in Escherichia coli (E. coli) as the surviving bacteria showed an increased fitness after extended starvation, enabling them to grow and displace the parent as the majority population.
Streptococcus mutans (S. mutans) frequently experience starvation naturally within a caries lesion. During caries removal, some S. mutans cells are left within the tooth, and presumably experience long-term starvation. This study investigated whether the surviving S. mutans showed an increased fitness and GASP phenotype existed within S. mutans.
Methods: Metabolic activity was used as the indicator for bacterial fitness. Metabolic activity of cells was assessed by using a luciferase reporter system integrated in L-lactate dehydrogenas (ldh) promoter within S. mutans cells. Ldh-luciferase strain of S. mutans was grown in BHI. Numbers of viable cells and metabolic activities at different time points were obtained by plating and luciferase assay. To study GASP phenotype, the method reported for E. coli (Finkel and Kolter, 1999) was followed using Kanamycin resistance strain (Kanr) and the parent strain of S. mutans with little modification. As positive control, Kanamycin resistance strain and parent strain of E. coli were used for the experiment. Expressions of regulatory genes within S. mutans were studied using real-time RT-PCR to explore the genetic mechanisms.
Results: After 25-day starvation 95% of surviving bacteria were metabolically active comparing to 18% after 4-day starvation. Unlike E. coli cells, the surviving S. mutans did not take over the culture co-inoculated with parent strain after 10 days starvation. Changes in expression of regulatory genes were observed in surviving S. mutans cells.
Conclusions: Although the surviving cells of S. mutans after prolonged starvation seemed become more active metabolically, the GASP phenotype was not obvious within S. mutans cells.
In part supported by grant NIH DE013298 and OVPR/UM U016834