Bacterial Color Response to Hexavalent Chromium, $Cr^{6+}$

A blue pigment-producing bacterium, Vogesella indigofera, was isolated and quantified for the relationship between its synthesis of a blue pigment and exposure concentrations of $Cr^{6+}$. The concentration of $Cr^{6+}$ and the percentage of blue colonies on agar plates was negatively correlated ($r^{2}$ =-0.8683). Critical concentrations inhibiting bacterial pigment production were found to be between 100-150 $\mu\textrm{g}$ $Cr^{6+}$/ml on agar plates and 200-300 $\mu\textrm{g}$ $Cr^{6+}$/ml in liquid culture. As the blue color is characteristic and easily observable, the bacterium Vogesella indigofera may have potential applications in the detection and monitoring of environmental pollution.