N-acyl homoserine lactone quorum sensing signals were detectable in an in vitro dental plaque community grown under 5% carbon dioxide but not under anaerobic conditions, according to a recent study.
A supragingival plaque–derived multispecies community showed oxygen-dependent N-acyl homoserine lactone (AHL) activity, and manipulating AHL signaling shifted biofilm composition and function. Under 5% carbon dioxide (CO2), C6 homoserine lactone (HSL) was detected, and biosensor activity corresponded to approximately 100 nM C6 HSL equivalents; AHL-degrading lactonases reduced this signal by 86% with SsoPox and by 49% with GcL, supporting biologically relevant AHL activity in this condition.
Disrupting AHL signaling under 5% CO2 most strongly affected biofilms. Both lactonases altered biofilm community structure, increased the combined relative abundance of early-colonizer taxa by about 6% (from about 77% to 83%), and reduced Shannon diversity.
These compositional changes were accompanied by functional shifts. SsoPox reduced biofilm biomass by 57.3%, from 2.18 mg in controls to 0.93 mg. After anaerobic incubation with 0.2% sucrose for 4 hours, lactate increased from 0.95 mM in controls to 1.27 mM with SsoPox, a 33.6% increase, and to 1.84 mM with GcL, a 92.5% increase.
In anaerobic cultures, endogenous AHLs were not detected, but exogenous AHLs altered anaerobic biofilm beta diversity. AHL treatment eliminated Haemophilus (about 5.3% in controls) and increased Porphyromonas (about 7.0% to about 7.6% to 7.7%); C6 AHL also increased Veillonella (8.5% to 8.8%).
To generate this data, investigators cultured a previously described supragingival plaque community pooled from 5 healthy volunteers in saliva-supplemented medium at 37 °C under 5% CO2 or anaerobic conditions. AHL activity was assessed by high-performance liquid chromatography–mass spectrometry and an Escherichia coli GFP biosensor (detection range 10 nM to 1 μM).
Under 5% CO2, cultures received SsoPox or GcL lactonases (200 μg/mL) or inactive lactonase control. Under anaerobic conditions, cultures were treated with exogenous C6 HSL or C12 HSL (10 μM) or DMSO. Biofilm and planktonic fractions underwent 16S ribosomal RNA V4 sequencing, and Bray-Curtis principal-coordinate analysis with analysis of similarity and analysis of molecular variance evaluated treatment effects.
Oxygen availability strongly shaped baseline community structure, with Gram-positive commensals and early colonizers predominating under 5% CO2 and Gram-negative genera associated with later succession enriched under anaerobic conditions.
Limitations included the use of an in vitro culture system that does not fully reproduce the physiologic complexity of dental plaque in vivo. Methodological constraints may have influenced signal detection, as the extraction approach favored short-chain AHLs and the biosensor reported C6-HSL equivalents rather than specific AHL identities or concentrations. In addition, community profiling based on 16S V4 sequencing limited taxonomic resolution and did not identify individual AHL producers, receptors, or downstream quorum sensing pathways. The observed compositional changes were statistically significant, but their relevance to periodontal disease requires evaluation in models that more closely approximate clinical settings.
“Targeting [quorum sensing] may offer a novel strategy for managing oral biofilms and preventing periodontal disease,” the authors noted.
Full disclosures can be found in the published study.
Source: npj: biofilms and microbiomes
