Bioaccumulation of silver and the isolation of metal-binding protein from P-diminuta

A silver uptake study by Pseudomonas diminuta was carried out by growing the bacteria in a chloride-free medium (CFM) containing silver ions (50 muM) in a batch culture. From the results, it was found that higher amounts of silver were accumulated inside the cell during early exponential phase compared to the amount bound at the cell surface. This suggested a possible mechanism for metal uptake during bacterial growth. In view of this, attempts were made to isolate proteins which might be associated with silver-binding properties from cultures of P. diminuta grown in the presence and absence of silver. The proteins were first extracted from the bacterial cultures by precipitation with ammonium sulfate followed by purification using isoelectric focussing and SDS-PA GE. Results of the experiment showed the presence of low molecular weight and high molecular weight proteins containing silver with pl values ranging from 2.0 to 9.0 for bacteria grown in the presence of silver.