Simultaneous spatiotemporal mapping of in situ pH and bacterial activity within an intact 3D microcolony structure.
Biofilms are comprised of bacterial-clusters (microcolonies) enmeshed in an extracellular matrix. Streptococcus mutans can produce exopolysaccharides (EPS)-matrix and assemble microcolonies with acidic microenvironments that can cause tooth-decay despite the surrounding neutral-pH found in oral cavity. How the matrix influences the pH and bacterial activity locally remains unclear. Here, we simultaneously analyzed in situ pH and gene expression within intact biofilms and measured the impact of damage to the surrounding EPS-matrix. The spatiotemporal changes of these properties were characterized at a single-microcolony level following incubation in neutral-pH buffer. The middle and bottom-regions as well as inner-section within the microcolony 3D structure were resistant to neutralization (vs. upper and peripheral-region), forming an acidic core. Concomitantly, we used a green fluorescent protein (GFP) reporter to monitor expression of the pH-responsive atpB (PatpB::gfp) by S. mutans within microcolonies. The atpB expression was induced in the acidic core, but sharply decreased at peripheral/upper microcolony regions, congruent with local pH microenvironment. Enzymatic digestion of the surrounding matrix resulted in nearly complete neutralization of microcolony interior and down-regulation of atpB. Altogether, our data reveal that biofilm matrix facilitates formation of an acidic core within microcolonies which in turn activates S. mutans acid-stress response, mediating both the local environment and bacterial activity in situ.
Biofilm Research Labs, Levy Center for Oral Health, Department of Orthodontics and Divisions of Pediatric Dentistry &Community Oral Health, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Geelsu
G
Hwang
Biofilm Research Labs, Levy Center for Oral Health, Department of Orthodontics and Divisions of Pediatric Dentistry &Community Oral Health, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Yuan
Y
Liu
Biofilm Research Labs, Levy Center for Oral Health, Department of Orthodontics and Divisions of Pediatric Dentistry &Community Oral Health, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Dongyeop
D
Kim
Biofilm Research Labs, Levy Center for Oral Health, Department of Orthodontics and Divisions of Pediatric Dentistry &Community Oral Health, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Victor
V
Sun
Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA.
Alejandro
A
Aviles-Reyes
Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA.
Jessica K
JK
Kajfasz
Department of Oral Biology, University of Florida College of Dentistry, Gainesville, FL, USA.
Jose A
JA
Lemos
Biofilm Research Labs, Levy Center for Oral Health, Department of Orthodontics and Divisions of Pediatric Dentistry &Community Oral Health, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA.
Hyun
H
Koo
D000251:Adenosine Triphosphatases / Q000235:genetics; D018441:Biofilms; D004058:Diffusion; D005109:Extracellular Matrix / Q000737:chemistry / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000502:physiology*; D013295:Streptococcus mutans / Q000166:cytology* / Q000235:genetics / Q000502:physiology*
D011135:Polysaccharides, Bacterial; C098632:exopolysaccharide, Streptococcus; D000251:Adenosine Triphosphatases