You can use sterile Halophilic Agar Medium. The halophilic agar medium containing (gm/L) Peptone - 5, Yeast extract - 3, CaCl2 - 0.1, Potassium chloride 5, MgSO4
- 6, NaCl- 30, Agar - 20. for isolation of rhizospheric bacteria.
As the composition of minerals in environmental samples can vary, what I usually do is to use the water or a soil extract from the same place as the basal medium.