Application of bacterial biomass as a potential metal indicator

Bioindicators are biological systems which can be used to indicate the presence of certain elements. The basis of indication are the changes that occur either in their metabolism or in phenotype of the organisms due to the uptake and accumulation of these elements. The threat of environmental pollution due to enhanced availability of both essential and toxic metals is a matter of great concern. Application of any remedial measure requires proper assessment of the contaminated sample. We used a multimetal-resistant organism, Pseudomonas stutzeri RS34, to indicate the presence of Cu2+ and Co2+ in solution as well as in an industrial effluent. Metal resistance mechanism in this organism is based on biosorption and strain RS34 showed preferential absorption for Cu2+. This accumulation imparted green colour to the biomass in a concentration-dependent manner (2.0 ppm and higher concentration). The colour is seen even in bimetal or multimetal conditions, where Co2+, Zn2+ and Mn2+ were present along with Cu2+ and is also observed in an effluent. Co2+ could also be detected by the biomass acquiring a characteristic pink colour. We thus propose that strain RS34 can be employed as bioindicator of certain metals simply based on appearance of colour. This method is not only economical, but also quick and easy to operate.