Red Fluorescence from Biofilms of Peptostreptococcus Micros and Porphyromonas Gingivalis

In a previous study red fluorescence was found from Peptostreptococcus micros grown adjacent to Porphyromonas gingivalis and this red fluorescence was enhanced and seen at longer incubation times when in close proximity of P. gingivalis (van der Veen and Luppens, J Dent Res 86 (spec Issue A): 1816, 2007). Objectives: This study aimed at investigating red fluorescence of P. micros and P. gingivalis grown as single and dual species biofilm in 96-wells micro-titer plates. Method: Single or dual species biofilms of  P. micros (dsmz 20468) and P. gingivalis strains (HG 91, W50 wild type and K1A kgp knockout mutant (kgp::erm) of W50 (Aduse-Opoku et al. Microbiology 2000;146: 1933-1940)) were grown in micro-titer plates in Colombia broth (CB with 5µg/ml hemine and 1µg/ml menadione) in an anaerobic chamber (10%CO₂) at 37 ^oC for 24, 48, 72 and 96 hours. Each well of the plates was inoculated with 5.10⁷ CFU of P. micros and/or P. gingivalis in 200µl CB. Each 24 hours medium was refreshed and plates were assessed for fluorescence (l_ex=405nm, l_em=635nm) corrected for OD₆₂₀. Results: Red fluorescence was observed at all timepoints for single species biofilms of P. micros and P. gingivalis. Fluorescence for P. micros increased upto 48 hours and then decreased in time. Levels of fluorescence for P. micros grown in dual species biofilms with P. gingivalis w50 were significantly higher after 24 and 48 hours of growth than for single species biofilms, but not for HG91 and K1A. Levels of red fluorescence for all P. gingivalis strains was similar and significantly lower than that of P. micros after 24 hrs and slowly decreased with growth time. Conclusion: The red fluorescence of P. micros is a property of P. micros itself and this may be enhanced by the presence of P. gingivalis w50, but the mechanism remains unknown.