Assessing in vitro solubilization potential of different zinc solubilizing bacterial (ZSB) isolates

Zinc solubilizing ability of Bacillus sp. and Pseudomonas sp. was assessed using zinc oxide, zinc sulphide (sphalerite) and zinc carbonate in both plate and broth assays. ZSB-O-1 (Bacillus sp.) showed highest dissolution in the zinc sulphide (Sphalerite ore), with 2.80 cm of dissolution zone and 14.50 cm(2) of area in the plate assay and 13.60 mg kg(-1) of zinc in the broth assay oil the 15(th) day after inoculation. The ZSB-S-2 (Pseudomonas sp.) showed more solubilizing ability in the zinc oxide, with 3.30 cm clearing zone and 20.43 cm(2) area in the plate assay and 16.40 mg kg(-1) of zinc in the broth assay over the same inoculation period. The isolate ZSB-S-4 (Pseudomonas sp.) has highest solubilizing potential in zinc carbonate With 6.20 cm of dissolution zone and 13.40 cm(2)area in the plate assay and 13.40 mg kg(-1) of zinc in the broth assay. Thus, the solubilization potential varies among different Cultures. The solubilization might be Clue to production of acids by the culture, since the pH of the Culture broth has been shifted form 7.0-7.3 to 4.8-6.5 after 15 days of inoculation. The zinc tolerance limit for two Cultures (ZSB-O-1 and ZSB-S-2) was studied and determined to be upto 100 mg kg(-1) of zinc in the in vitro broth assay.