EVIDENCE FOR CELL-DENSITY DEPENDENT RESPONSES IN PARACOCCIDIOIDES BRASILIENSIS

Luis Felipe Vieira Souza E Silva (UnB); Lorena Silveira Derengowski (UnB); Natasha Valladares Kerr (UnB); Ildinete Silva-pereira (UnB)

Quorum-sensing (QS) is a mechanism of microorganisms communication based on cell density. Among other effects, QS regulates the expression of some genes, resulting in phenotypic modifications. This process is well known in bacteria and has also been described in fungi such as Candida albicans and Histoplasma capsulatum. In the present work, we analysed the presence of such process in the dimorphic fungus Paracoccidioides brasiliensis, the etiologic agent of the most prevalent systemic mycosis in Latin America, paracoccidioidomycosis (PCM). The P. brasiliensis Pb18 and Pb192 strains were grown for 6 days at 37°C in YPD medium. The conditioned medium (CM) was then obtained by collecting and filtering the supernatant of these cultures. Cultures of Pb18 at different inoculum concentrations were treated with 0%, 25% and 50% of both, Pb18 and Pb192 CM. Alternatively, the same experiment was performed using Pb01 and Pb3 strains. The growth rate of these cultures was measured daily observing the optical density at 630 nm and by MTT assay. The effects of the CM in the dimorphic transition were also observed using optical microscopy. Our results shown an enhanced growth rate in treated cultures with Pb18 CM at low initial inoculum concentrations (<104cells/mL). Similar results were also obtained to Pb01 and Pb3 strains cultivated in the presence of 50% of Pb18 CM.  Although no significant results were observed in the dimorphic transition, the same growth enhancement was observed in these experiments, supporting our previous observations. Based in these results, we tested if this Pb18 CM autoclaved for 15 minutes would conserve the same effects, and the results revealed that it didn’t. Our results reveal a possible QS phenomenon in P. brasiliensis, which is probably mediated by a thermolabile molecule.