Etude de l’activité anti-Candida albicans des microorganismes isolés à partir du sol des zones arides

Abstract

"The exploration of soil samples from a palmary in the region of TOLGA, a salt lake in the region of EL MRIERE, a salt lake of AIN M’LILA and the rhizosphere of an adjacent plant led the obtaining of 92 bacterial and 16 fungal isolates. Three Bacillus isolates and one fungus belonging to the genus Eurotium are screened, in vitro, for their strong antagonist effect against Candida albicans. Molecular identification of isolates by 16S rDNA and 18S rDNA sequences analysis for bacteria and fungus, respectively, showed that they were closely related to Bacillus subtilis, Bacillus mojavensis, Bacillus niabensis and Eurotium repens. Screened bacteria develop in flasks conditions high sporulation yields varying between 8.33 % and 20 %. The halophyte character of E. repens was investigated by their capacity to grow on salt media (80g/l for B. niabensis and 200g/l for E. repens).To our knowledge, these obtaining data are shown for the first time in this study. The screened bacteria are able to produce cell wall degrading enzymes (protease and cellulase), furthermore, they produce lipopeptides on optimized medium in flasks and fermenter conditions. Interestingly, the present work is the first to reveal the possibility of isolating B. niabensis from soil and its ability to produce lipopeptides antifungal molecules, also. In another side, Eurotium repens was subjected to a comparative study characterizing its growth and capacity to produce metabolites in diverse culture conditions. In fact, E. repens develops better in salt rich medium (3.2g/L), comparing to salt poor medium (0.36g/L). In addition, this work revealed that metabolites produced in stress conditions differ from those produced in favorable conditions. Isolation and identification of these metabolites by CCM, HPLC-UV, HPLC/MS and HPLC/MS2 techniques showed the presence of tryptophan, cinnamic acid (in salt rich medium) and oleic acid (in poor salt medium). These results are shown for the first time in the present study."