Évaluation de la production et de l'activité antimicrobienne de la pyoverdine chez des isolats de Pseudomonas fluorescens rhizosphériques

Abstract

Pyoverdins are siderophores secreted by fluorescent Pseudomonas. They are low molecular weight and high affinity iron chelators produced under iron restricted conditions. Their importance extends their applications to agriculture, biotechnology and medicine. In the present work, our goal was to evaluate the production of Pyoverdins by Pseudomonas fluorescens and to examine their antimicrobial activity. A total of 14 fluorescent Pseudomonas were isolated from the roots of a wild grass (rat barley = Hordeum murinum) in addition to two isolates of the same species previously identified to P. fluorescens. The application of a set of identification tests allowed us to belong four isolates among the 14 to P. fluorescens species. The six P. fluorescens strains were used to determine their antagonistic activity against 8 pathogenic strains using the crossed streaks method, once on the standard King B medium and again on the same medium plus FeCl3. The results showed inhibition zones of 5 to 34 mm in the non-iron added medium with appearance of a greenish-yellow fluorescence. An isolate (PK) exerted its inhibition in the presence and absence of Fe3+ which excludes the role of the pyoverdin in this action. An UV / Visible spectrophotometry analysis of the supernatants of the six P. fluorescens grown in the succinate medium, showed spectra similar to the pyoverdin spectrum in four isolates and two different spectra in two others. The pyoverdin dosage determined that the P11 isolate is the most productive and it is the supernatant of this strain that showed the greatest inhibition against P. mirabilis ATCC 35659 and C. albicans ATCC 10231 with 16 and 15 mm in diameter respectively. The PK strain producing pyoverdin and phenazine compounds gave an 18 mm inhibition zone with P.mirabilis ATCC 35659. Pyoverdin of the isolate P11 produced on king B medium and extracted by solid / liquid extraction showed 15 mm inhibition zones with P. mirabilis ATCC 35659 and 14 mm with C. albicans ATCC 10231. The API 20 NE Gallery used to identify the P11 isolate yielded results corresponding to P. fluorescens species.