Adaptation to simulated microgravity in Streptococcus mutans.

Area of Science:

• Microbiology
• Space Biology
• Genomics

Background:

• Long-term space missions are associated with a higher incidence of oral diseases in astronauts.
• Dental caries, caused by Streptococcus mutans, poses a significant threat to astronaut health during extended spaceflight.
• Understanding bacterial adaptation to spaceflight environmental stressors is crucial for mitigating health risks.

Purpose of the Study:

• To investigate the adaptive response of Streptococcus mutans to simulated microgravity.
• To identify genetic and phenotypic changes in S. mutans under spaceflight conditions.
• To assess the impact of simulated microgravity on the virulence factors of S. mutans.

Main Methods:

• Experimental evolution of Streptococcus mutans for 100 days in simulated microgravity using high aspect ratio vessels.
• Whole genome resequencing to identify genetic mutations and adaptive changes.
• Phenotypic analysis including antibiotic susceptibility, acid tolerance, and adhesion assays.

Main Results:

• S. mutans evolved unique variants in genes pknB, SMU_399, and SMU_1307c under simulated microgravity.
• Mutations in SMU_399, ptsH, and rex were detected earlier in microgravity populations compared to controls.
• While antibiotic susceptibility remained largely unchanged, acid tolerance and adhesion decreased significantly in adapted populations.

Conclusions:

• Simulated microgravity induces specific genetic adaptations in Streptococcus mutans.
• The study highlights the importance of parallel normal gravity controls, multi-time-point sequencing, and biological replicates for accurate microgravity adaptation studies.
• Findings underscore the potential for altered oral pathogen behavior in space, necessitating further research for astronaut health protection.