Effet du stress salin sur la croissance et la solubilisation du phosphate par des rhizobactéries

Abstract

The use of microorganisms from rhizosphere is the best way to improve biological solubilization of phosphorus in saline soil to reduce salt stress which can affect growth and activity of rhizobacteria. The aim of our present study is to evaluate the effect of salt stress on the growth and phosphate solubilization of phosphate tricalcique by five phosphate solubilizing bacteria isolated from saline soil (R1, R2, R3, R4, R5) usingincreasing concentrations of NaCl(0, 100, 200…...900mM). The ability of phosphate solubilization by the five isolates has been tested on PVK solid medium where the R3isolate was considered to be the most effective one with a maximum efficiency of 366.66%. The salt tolerance of bacterial isolates in nutrient broth revealed variable results of optical density, the value of the highest optical density corresponding to maximum growth was obtained from the isolate R4 (DO: 1,604) with 400 mM of NaCl. The quantities of released phosphorus by bacterial cultures in NBRIP liquid medium under salt stress ranged from 135, 429μg /ml and 879,714μg. The highest rate was detected with isolates R2 and R4 with a significant amount of soluble phosphorus of 879,714μg/ml and 834,476μg/ml respectively with 300 and 400 mM of NaCl. pH values of bacterial cultures ranged from 5.337 to 3.72 were obtained which with increasing of phosphate solubilization rate. The results obtained show that the bacterial isolates used in this study tolerated high levels of salt and were able to solubilize insoluble phosphate even at high NaCl concentrations.