Autoinducer-2 detection among commensal oral streptococci is dependent on pH and boric acid

Abstract

Autoinducer-2, considered a universal signaling molecule, is produced by many species of bacteria; including oral strains. Structurally, autoinducer-2 can exist bound to boron (borated autoinducer-2). Functionally, autoinducer-2 has been linked to important bacterial processes such as virulence and biofilm formation. In order to test production of autoinducer-2 by a given bacterial strain, a bioassay using marine bioluminescent bacteria Vibrio harveyi as a reporter for autoinducer-2 has been designed. We hypothesize that pH adjustment and addition of boron are required for optimal bioluminescence and accurate autoinducer-2 detection. Using this reporter strain we tested autoinducer-2 activity from two oral commensal species, Streptococcus gordonii DL1 and Streptococcus oralis 34. Spent broth was collected and adjusted to pH 7.5 and supplemented with boric acid prior to measuring autoinducer- 2 activity. Results show that low pH inhibits bioluminescence of the reporter strain, but pH 7.5 allows for bioluminescence induction and proper readings of autoinducer-2 activity. Addition of boric acid also has a positive effect on bioluminescence allowing for a more sensitive detection of autoinducer-2 activity. Our data suggests that although autoinducer-2 is present in spent broth, low pH and/or low levels of boric acid become an obstacle for proper autoinducer-2 detection. For proper autoinducer-2 detection, we propose a protocol using this bioassay to include pH adjustment and boric acid addition to spent broth. Studies on autoinducer-2 activity in several bacteria species represent an important area of study as this universal signaling molecule is involved in critical bacterial phenotypes such as virulence and biofilm formation.

Efficacy of Preprocedural Boric Acid Mouthrinse in Reducing Viable Bacteria in Dental Aerosols Produced during Ultrasonic Scaling

“…BA 1 mM addition enhanced the bioluminescence and allowed better binding and detection of streptococci strains. [ 21 ]…”

D-Ribose Interferes with Quorum Sensing to Inhibit Biofilm Formation of Lactobacillus paraplantarum L-ZS9

“…AI-2 activity is usually detected by using the reporter strain V. harveyi BB170 (sensor 1- sensor 2+ ), which only recognizes AI-2 ( Vilchez et al, 2007 ). However, a high concentration of glucose and acidic pH can inhibit AI-2 activity ( DeKeersmaecker and Vanderleyden, 2003 ; Turovskiy and Chikindas, 2006 ; Cuadra et al, 2016 ). Therefore, as for lactic acid bacteria, AI-2 activity detection is difficult under traditional cultural conditions and CF preparation.…”

Inhibitory effect of Lonicera japonica flos on Streptococcus mutans biofilm and mechanism exploration through metabolomic and transcriptomic analyses

“…Then, 1.0 mL of tested samples, negative control, positive control, and chemically synthesized pure AI-2 (10 μM) were added separately to each tube ( Supplementary Figure S2 ). The luminescence value (RL) (SpectraMax ® i3, Molecular Devices, Shanghai, China) was measured in photons/s mode every 60–120 min for a total of 8 h. AI-2 content was determined as described ( Vilchez et al, 2007 ; Cuadra et al, 2016 ; Muras et al, 2018 ; Zhang Y. et al, 2022 ). The relative luminescence intensity (RLI) and the content of AI-2 was determined as follows:…”