Résumé:
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.
