Metabolic Inhibition of a Toluene-Enriched Microbial Population Due to Lead(Pb2+); Verification of a Free Metal ION Toxicity Model

摘要

A dissolved oxygen probe and an ion specific electrode were used to study thelead-induced metabolic inhibition in a toluene-enriched microbial population. Predicted toxicity values were compared to the actual toxicity responses using a free metal ion toxicity model (TM) which linked metabolic inhibition with lead activity. Experimentally derived values for the model parameters (lead activity and a lead distribution coefficient) were used in the TM. It was postulated that cellular metabolism is disrupted by the conformational changes to the cell's plasma membrane produced by lead ion adsorption. The predicted toxicity values were higher than the actual toxicity response. This is expected since the TM did not distinguish between essential and non-essential cellular ligands. Moreover, lead-induced metabolic inhibition appears to be pH dependent as the TM predicted. An adsorption experiment suggested that the microbial mass has two lead binding sites: tightly bound ligands and loosely bound ligands. The tightly bound ligand sites appeared to be saturable. No evidence of saturation was observed in tile loosely bound ligand sites. Contrary to expectations, the loosely bound ligand sites appear to be more essential to cellular metabolism than the tightly bound ligand sites.