Lead (II) Ion Inhibition of Respiration and Replication in a Toluene-Enriched Microbial Population

ABSTRACT Bioremediation is inhibited in mine leachate water because of high concentrations of heavy metals and low pH. Inhibition of cellular respiration (A N ) and replication (U N ) by lead ions were measured at pH values near 5 for a mixed microbial culture from a wastewater treatment plant, grown aerobically using toluene as the primary carbon source. Gram-negative microorganisms dominated the toluene-selected microbial population. Microorganisms sequestered lead at binding sites having two different strengths. The stronger binding sites were saturated at about 0.5 mg/L Pb(II) concentration; no evidence of saturation of weaker binding sites was observed up to 15 mg/L of Pb(II). Most of the weak-binding capacity for lead was extracellular, which increased with lead ion concentration without saturating; the intracellular portion of the weak-binding capacity saturated at about 1.0 mg of lead per milligram of dry cells. Lead toxicity, measured by inhibition of respiration and replication, increased as lea...