Phenotypic expression of Vogesella indigofera upon exposure to hexavalent chromium, Cr6+

Abstract

A eubacterium producing a blue pigment was isolated from a drinking water filter, and subsequently identified as Vogesella indigofera. This bacterium was further investigated for its morphological and biochemical characteristics after exposure to hexavalent chromium, Cr6+. The threshold Cr6+ concentration inhibiting the pigment production by V. indigofera was 200-300 μg ml-1 in liquid cultures of nutrient broth and 100-150 μg ml-1 on nutrient agar plates. The Cr6+ concentration preventing V. indigofera growth was 300-400 μg ml-1 in liquid cultures, but greater than 150 μg ml-1 on agar plates. Moreover, rugose colonies without the blue pigmentation were observed on agar plates amended with 150 (μg Cr6+) ml-1. The biochemical utilization profiles of the colonies without pigmentation did not differ from the original pigment-producing ones, indicating phenotypic plasticity of this bacterium. The difference of phenotypic expression of V. indigofera under various Cr6+ concentrations might have potential application as a pollution bioindicator for heavy metals.