Investigation of simulated microgravity effects on Streptococcus mutans physiology and global gene expression

• Published in: NPJ microgravity 2017-01, Vol.3 (1), p.4-10, Article 4
• Main Authors: Orsini, Silvia S., Lewis, April M., Rice, Kelly C.
• Format: Article
• Language: English
• Subjects: 631/326; 692/420/254; Applied Microbiology; Bacteria; Biomedical and Life Sciences; Biotechnology; Carbohydrate metabolism; Classical and Continuum Physics; Dental caries; Dental disorders; Gene expression; Gravity; Hydrogen peroxide; Immunology; Life Sciences; Metabolism; Metabolites; Microgravity; Periodontics; Physiology; Protein turnover; Space Exploration and Astronautics; Space flight; Space Sciences (including Extraterrestrial Physics; Streptococcus infections; Streptococcus mutans; Teeth
• ISSN: 2373-8065; 2373-8065
• DOI: 10.1038/s41526-016-0006-4

Astronauts have been previously shown to exhibit decreased salivary lysozyme and increased dental calculus and gingival inflammation in response to space flight, host factors that could contribute to oral diseases such as caries and periodontitis. However, the specific physiological response of caries-causing bacteria such as Streptococcus mutans to space flight and/or ground-based simulated microgravity has not been extensively investigated. In this study, high aspect ratio vessel S. mutans simulated microgravity and normal gravity cultures were assessed for changes in metabolite and transcriptome profiles, H 2 O 2 resistance, and competence in sucrose-containing biofilm media. Stationary phase S. mutans simulated microgravity cultures displayed increased killing by H 2 O 2 compared to normal gravity control cultures, but competence was not affected. RNA-seq analysis revealed that expression of 153 genes was up-regulated ≥2-fold and 94 genes down-regulated ≥2-fold during simulated microgravity high aspect ratio vessel growth. These included a number of genes located on extrachromosomal elements, as well as genes involved in carbohydrate metabolism, translation, and stress responses. Collectively, these results suggest that growth under microgravity analog conditions promotes changes in S. mutans gene expression and physiology that may translate to an altered cariogenic potential of this organism during space flight missions. Microbiology: Cavities-causing bacteria altered by space-like conditions The gene expression patterns, metabolism and physiology of tooth cavities-causing microbes change in a space-like gravity environment. These findings could help explain why astronauts are at a greater risk for dental diseases when in space. Kelly Rice and colleagues from the University of Florida, Gainesville, USA, cultured Streptococcus mutans bacteria under simulated microgravity and normal gravity conditions. The bacteria grown in microgravity were more susceptible to killing with hydrogen peroxide, tended to aggregate in more compact cellular structures, showed changes in their metabolite profile and expressed around 250 genes at levels that were either much higher or lower than normal gravity control cultures. These genes included many involved in carbohydrate metabolism, protein production and stress responses. The observed changes collectively suggest that space flight and microgravity could alter the cavities-causing potential of S. mutans .