Sang-Joon Ahn


SJA Updated PhotoResearch Associate Professor

Department of Oral Biology
1395 Center Drive, D5-29
Box 100424
Gainesville, FL 32610-0424
Phone: 352-273-8834

Main Interests

My research area is to elucidate the regulatory pathways of oral bacteria, with particular focus on biofilm formation and stress tolerance that can modulate the virulence of oral bacteria and enhance the pathogenic potential of oral biofilms. As a standpoint protein for this research, I have been working on AtlA protein, an apparent autolysin of Streptococcus mutans, which was originally identified as a surface-associated protein in our laboratory. AtlA protein is absolutely required for normal biofilm formation, biogenesis of a normal cell surface, and autolysis in S. mutans. AtlA activity is subject to control by the VicRK two-component system (TCS), which is known to play critical roles in pneumococcal virulence. Continuous studies have addressed several key issues regarding the regulation of AtlA and provided further support for the interconnectedness of this pathway with the expression of other virulence attributes and pathways, including genetic competence and exopolysaccharide production by S. mutans. More recently, oxygen was revealed to be a key environmental factor that strongly influences cell envelope composition and biofilm development via the VicRK TCS and the AtlA pathway. Studies are ongoing to further dissect the regulation and processing of AtlA and to evaluate the potential utility of AtlA as a target to disrupt S. mutans pathogenesis.

Stemming from the original AtlA work, another major research area is to investigate the molecular basis for regulation of autolysis of S. mutans by gene products that have major effects on traits related to virulence. This research focuses on the characterization of a pair of dicistronic operons, lrg and cid-like, that significantly affected autolysis and biofilm formation by S. mutans. The pair of operons shares structural features with the bacteriophage-encoded holin family of proteins that are involved in the control of bacteriophage-mediated cell death and lysis. Thus, research on this system has led to the proposal that it comprises the molecular components of bacterial programmed cell death (PCD), which is likely to interconnect with the ability of this organism to rapidly and efficiently cope with changes in the environment. The development of biofilms is believed to involve the programmed elimination of cells by bacterial PCD, or autolysis. Indeed, the ability to eliminate individual bacterial cells in response to damage induced by a variety of harmful or stressful conditions may be critical for survival and persistence of pathogenic biofilms, including S. mutans. In addition to controlling autolysis, the lrg/cid-like operons play unique and important roles in S. mutans, and are regulated in a highly complex manner with multiple different modes of control, including a signal transduction system, quorum-sensing, and carbohydrates. Better understanding of how the Lrg/Cid-like system of S. mutans may contribute to establishment, persistence and virulence in oral environments, will provide a comprehensive picture of the way in which S. mutans integrates environmental or physiological signals during biofilm maturation, and ultimately enhance our understanding of the pathogenic properties of S. mutans and illuminate the way to new strategies to control oral diseases.

Recent Publications

  • Son, M., Kaspar, J., Ahn, S-. J., Burne, R. A., and Hagen, S. J. 2018. Threshold regulation and stochasticity from the MecA/ClpCP proteolytic system in Streptococcus mutans competence. Mol Microbiol doi: 10.1111/mmi.13992.
  • Huang, X., Browngardt, C. M., Jiang, M., Ahn, S-. J, Burne, R. A., and Nascimento, M. M. 2018. Diversity in antagonistic interactions between commensal oral streptococci and Streptococcus mutans. Caries res. 52:88-101.
  • Ahn, S-.  J., Gu, T., Koh, J., and Rice, K. C. 2017. Remodeling of the Streptococcus mutans proteome in response to LrgAB and external stresses. Sci Rep 7: 14063, doi:10.1038/s41598-017-14324-w.
  • De Furio, M., Ahn, S-. J., Burne, R. A., and Hagen, S. 2017. Oxidative stressors modify the response of Streptococcus mutans to its competence signal peptides. Appl Environ Microbiol. 83(22) pii: e01345-17. doi: 10.1128/AEM.01345-17.
  • He, J., Kim, D., Zhou, X., Ahn, S-., J., Burne, R. A., Richards, V., and Koo, H. RNA-seq reveals enhanced sugar metabolism in Streptococcus mutans co-culturing withCandida albicans within mixed species biofilms. 2017. Front Microbiol, doi: 10.3389/fmicb.2017.01036.
  • Rice, K. C., Turner, M. E, Gu, T., and Ahn, S-. J. 2017. Modification of the Streptococcus mutans transcriptome by LrgAB and environmental stressors. 3(2): e000104,Microb Genom,  doi: 10.1099/mgen.0.000104.
  • Ahn, S-. J, and Rice, K. C. 2016.  Understanding the Streptococcus mutans Cid/Lrg System through CidB function. Appl Environ Microbiol. 82:6189-6203.
  • Kaspar, J, Kim, J. N, Ahn, S-. J, and Burne, R.A. 2016. An essential role for (p)ppGpp in the integration of stress tolerance, peptide signaling and competence development in Streptococcus mutans. Front Microbiol, 7:1162.
  • Moye, Z.D, Son, M, Rosa-Alberty, A.E, Zeng, L, Ahn, S-. J, Hagen, S. J, and Burne, R.A. 2016. Effects of carbohydrate source on genetic competence in Streptococcus mutans. Appl Environ Microbiol. 82:4821-34.
  • Huang, X., Palmer, S., Ahn, S-. J, Richards, V., Williams, M., L. Nascimento, M. M., and Burne, R. A. 2016. A Highly Arginolytic Streptococcus Species That Potently Antagonizes Streptococcus mutans. 82: 2187-201.
  • Son, M., Shields, R., Ahn, S-. J., Burne, R. A., and Hagen, S. J. 2015. Bidirectional signaling in the competence regulatory pathway of Streptococcus mutans. FEMS Microbiol. Lett. 82(7):2187-201. doi: 10.1128/AEM.03887-15.
  • Mogen, A. B., Chen, F., Ahn, S-. J., Burne, R. A., Wang, D., and K. C. Rice. 2015. Pluronics-formulated farnesol promotes efficient killing and demonstrates novel interactions with Streptococcus mutans biofilms. PLOS One, 10(7):e0133886. doi: 10.1371/journal.pone.0133886.
  • Son, M., Ghoreishi, D., Ahn, S-. J., Burne. R. A., and S. J. Hagen. 2015. Sharply tuned pH response of the genetic competence regulation in Streptococcus mutans: A microfluidic study of environmental sensitivity of comX. Appl. Environ. Microbiol. 81(16):5622-31.
  • Kim, J. N., Ahn, S-. J. and R. A. Burne. Genetics and physiology of acetate metabolism by the Pta-AckA pathway in Streptococcus mutans. 2015. Appl. Environ. Microbiol. 81(15):5015-25.
  • Kaspar, J., Ahn, S-. J. Palmer, S. R., Choi, S. C., Stanhope, M. J. and R. A. Burne. 2015. A Unique ORF within the comX gene of Streptococcus mutans Regulates Genetic Competence and Oxidative Stress Tolerance. Mol. Microbiol. 96:463-82.
  • Seaton, K.* Ahn, S-. J.*, Seaton, K. and R. A. Burne. (*, equally contributed). 2015. Regulation of competence and gene expression in Streptococcus mutans by the RcrR transcriptional regulator. Mol. Oral. Microbiol. 30:147-59.
  • Ahn, S-. J., Kaspar, J., Kim, J. N., Seaton, K., and R. A. Burne. 2014. Discovery of novel peptides dominantly regulating competence development in Streptococcus mutans. J. Bacteriol. 196: 3735-45.
  • Liao, S., Klein, M., Heim, K., Fan, Y., Bitoun, J., Ahn, S-. J., Burne, R. A., Koo, H., Brady, L. J., and Z. Wen. 2014. Streptococcus mutans extracellular DNA is upregulated during growth in biofilms, actively released via membrane vesicles, and influenced by components of the protein secretion machinery. J. Bacteriol. 196:2355-66.
  • Guo, Q*, Ahn, S-. J*, Kaspar, J., Zhou, X, and R. A. Burne. (*, equally contributed). 2014. Growth phase and pH influence peptide signaling for competence development in Streptococcus mutans. J. Bacteriol. 196: 227-36.
  • Cornejo, O. E., Lefébure, T., Pavinski Bitar, P. D., Lang, P., Richards, V. P., Eilertson, K., Do, T., Beighton, D., Zeng, L., Ahn, S-. J., Burne, R. A., Siepel, A., Bustamante, C. D., and M. J. Stanhope. 2013. Evolutionary and population genomics of the cavity causing bacteria Streptococcus mutans. Mol. Bio. Evo. 30: 881-93.
  • Ahn, S-. J., Qu, M-. D., Roberts, E., Burne, R. A., and K. C. Rice. 2012. Identification of the Streptococcus mutans LytST two-component regulon reveals its contribution to oxidative stress tolerance. BMC Microbiol. 12: 187.
  • Burne, R. A., Zeng, L., Ahn, S-. J., Palmer, S., Liu, Y, Lefebure, T, Stanhope, M., and Nascimento, M. 2012. Progress dissecting the oral microbiome in caries and health.Adv. Den. Res. 24:77-80.
  • Son, M., Ahn, S-. J., Guo, Q., Burne, R. A., and S. J. Hagen. 2012. Microfluidic study of competence regulation in Streptococcus mutans: environmental inputs modulate bimodal and unimodal responses. Mol. Microbiol. 86: 258-72.
  • Kim, J-. N, Ahn, S-. J., Seaton, K., Garrett, S., and R. A. Burne. 2012.  Transcriptional organization and physiological contributions to the relQ operon of Streptococcus mutans. J. Bacteriol. 194:1968-78.
  • Bitoun, J. P., Liao, S., Yao X, Ahn, S-. J., Isoda, R., Nguyen A. H., Brady, L. J., Burne, R. A., Abranches, J., and Z. T. Wen.  2012. BrpA is involved in regulation of cell envelope stress responses in Streptococcus mutans. Appl. Environ. Microbiol. 78: 2914-22.
  • Seaton, K, S-. J. Ahn, Sagstetter, A. M. and R. A. Burne. 2011. A transcriptional regulator and two ABS transporters link stress tolerance, (p)ppGpp genetic competence, and stress tolerance in Streptococcus mutans. J. Bacteriol. 193:862-74.
  • Burne, R. A., J. Abranches, S-. J. Ahn, J. A. Lemos, Z. T. Wen and L. Zeng. 2011. Functional genomics of Streptococcus mutans. In P. E. Kolenbrander (Ed) Genomic inquires into oral bacterial communities. ASM Press.
  • Ahn, S-. J., K. C. Rice, J. Oleas, K. W. Bayles, and R. A. Burne. 2010.  The Streptococcus mutans Cid and Lrg systems modulate virulence traits in response to multiple environmental signals. Microbiology,156: 3136-3147.
  • Wen, Z. T., D. Yates, S-. J. Ahn, and R. A. Burne. 2010. Biofilm formation and virulence expression by Streptococcus mutans is altered when grown in dual-species model. BMC Microbiol. 10:111.
  • Burne, R. A., Ahn, S-. J., Wen, Z. T., Zeng L., Lemos, J. A., Abranches, J., and Nascimento, M. 2009. Opportunities for disrupting cariogenic biofilms.  Adv. Den. Res. 21: 17-20
  • Ahn, S-. J., Ahn, S-. J., Browngardt, C. M., and R. A. Burne. 2009.  Changes in biochemical and phenotypic properties of  Streptococcus mutans growing with oxygen.Appl. Environ. Microbiol. 75:2517-2527.
  • Ahn, S-. J., Ahn, S-. J., Z. T. Wen, Brady, L. J., and R. A. Burne. 2008. Characteristics of biofilm formation by Streptococcus mutans in the presence of saliva. Infect. Immun. 76:4259-4268.
  • Ahn, S-. J., Z. T. Wen, and R. A. Burne. 2007. Effects of oxygen on virulence traits of Streptococcus mutans. J. Bacteriol. 189: 8519-8527.
  • Ahn, S-. J. and R. A. Burne. 2007.  Effect of oxygen on biofilm formation and the AtlA autolysin of Streptococcus mutans. J. Bacteriol. 189: 6293-6302.
  • Ahn, S-. J., C-. H. Yang, and D. A. Cooksey. 2007. Pseudomonas putida 06909 genes expressed during colonization on mycelial surfaces and phenotypic characterization of mutants. J. Appl. Microbiol. 103: 120-132.
  • Ahn, S-. J. and R. A. Burne. 2006.  The atlA operon of Streptococcus mutans: Role in autolysin maturation and cell surface biogenesis. J. Bacteriol. 188:6877-6888.
  • Ahn, S-. J., Z. T. Wen, and R. A. Burne. 2006. Multi-level control of competence development and stress tolerance in Streptococcus mutans UA159. Infect. Immun.  74:1631-1642.
  • Ahn, S-. J., J. A. C. Lemos, and R. A. Burne. 2005. Role of HtrA in growth and competence of Streptococcus mutans UA159. J. Bacteriol. 187: 3028-3038.
  • Brown, T. A. Jr, S-. J. Ahn, R. N. Roslyn, Y-. Y. M. Chen, J. A. Lemos, and R. A. Burne. 2005. A hypothetical protein of Streptococcus mutans is critical for biofilm formation. Infect. Immun. 73: 3147-3151.
  • Hwang, B-.K., S-. J. Ahn, and S-. S. Moon. 1994. Production, purification, and antifungal activity of the antibiotic nucleotide, tubercidin, produced by Streptomyces violaceoniger. Can. J. Bot. 72: 480-485.