Evaluation de l’effet du stress salin sur la production des métabolites secondaires chez les Pseudomonas fluorescents

Abstract

Pseudomonas are widely distributed microorganisms in various environments. These strains have a strong antimicrobial activity against pathogenic microorganisms through the production of secondary metabolites. Facing the increase in the phenomenon of antibiotic resistance, it has become necessary to explore new molecules and alternatives present in nature. In this perspective, the present study deals with the production of secondary metabolites under salt stress carried out on five Pseudomonas collected from sand under sea water. The effect of salinity was tested on these isolats with diffrent NaCl concentrations ranging from 1 to 7%. Secondary metabolites were produced on liquid Mueller-Hinton medium, which were then extracted using chloroform, the extract was then evaporated under vacuum and put into solution. The antimicrobial effect of the metabolite was tested on various Gram positive, Gram egative bacteria and on a yeast. The phenotypic tests identified all five isolates as Pseudomonas aeruginosa, two of these isolates (noted B and E) were found to be more productive. The results obtained for the salinity test showed that at a concentration of 1% of NaCl, strain B produced nearly 4 μg /ml of metabolites. For strain E, a concentration of metabolites close to 10 μg /ml was obtained at a concentration of 1.5% of NaCl. For the antagonistic activity, we were able to observe that the P. aeruginosa isolates exerted an antimicrobial activity on all target bacteria. The evaluation of the antimicrobial activity in vitro shows that the extracted secondary metabolites presented zones of inhibition that vary from 0.8 to 1.6 cm in diameter towards some of the pathogenic strains tested. These results illustrate the effect of salt stress on the production of secondary metabolites in P. aeruginosa isolates. It is possible to use the metabolites produced by P. aeruginosa as antimicrobial substances on certain pathogenic strains. One of the metabolites obtained is suspected to be pyocyanin.