Dipak Paul and Sankar Narayan Sinha

pp. 651 - 657

Abstract

Phosphates solubilizing bacterial (PSB) strains were isolated from the jute mill effluent discharge area of the Ganga
river water at Bansberia, West Bengal, India. Experimental studies found that the strain KUPSB16 was effective in solubilization of phosphate with phosphate solubilization index (SI) = 3.14 in Pikovskaya’s agar plates along with maximum solubilized
phosphate production of 208.18 μg mL^-1 in broth culture. Highest drop in pH value was associated with maximum amount of
phosphate solubilization by the PSB strain KUPSB16 where pH decreased to 3.53 from initial value of 7.0±0.2. The isolated
PSB strains were tested for tolerance against four heavy metals such as cadmium (Cd), chromium (Cr), lead (Pb) and zinc (Zn)
at concentrations 1-15 mM. The results showed that most of the PSB isolates grew well at low concentrations of heavy
metals and their number gradually decreased as the concentration increased. Isolated PSB strain KUPSB16 was tested for its
multiple metal resistances. Minimal inhibitory concentrations (MIC) for Cd²⁺, Cr⁶⁺, Pb²⁺ and Zn²⁺ in tris-minimal broth medium
were 4.2, 5.5, 3.6 and 9.5 mM respectively. The MIC values for the metals studied on agar medium was higher than in broth
medium and ranged from 4.8-11.0 mM. The isolated bacterial strain KUPSB16 was subjected to morphological, physiological
and biochemical characterization and identified as the species of the genus Bacillus. The phosphate solubilizing bacterium
possessing the properties of multiple heavy metal tolerance in heavy metal contaminated areas might be exploited for
bioremediation studies in future.

Keywords

• phosphate solubilizing bacteria
• heavy metal
• River Ganga