Lead Resistance in Two Bacterial Isolates from Heavy Metal-Contaminated Soils.

Area of Science:

• Environmental microbiology
• Bioremediation
• Toxic metal resistance

Background:

• Microbial resistance to toxic metals is crucial for environmental remediation.
• Lead resistance mechanisms in soil microorganisms are not well-understood.
• Environmental lead exposure influences microbial adaptation strategies.

Purpose of the Study:

• To investigate and compare lead resistance mechanisms in two distinct soil bacteria: Pseudomonas marginalis and Bacillus megaterium.
• To correlate observed resistance mechanisms with the specific lead contamination levels in their native soil environments.
• To elucidate novel microbial strategies for coping with lead toxicity.

Main Methods:

• Isolation and characterization of lead-resistant bacteria from metal-contaminated soils.
• Determination of lead resistance levels for soluble and total lead.
• Transmission Electron Microscopy (TEM) for visualizing intracellular lead accumulation.
• Polarization microscopy to analyze extracellular polymeric substance (EPS) production.

Main Results:

• Pseudomonas marginalis exhibited higher lead resistance (2.5mM total lead) than Bacillus megaterium (0.6mM total lead).
• P. marginalis showed extracellular lead exclusion, linked to high EPS production, from soil with high total but low soluble lead.
• B. megaterium demonstrated intracellular cytoplasmic accumulation of lead, with lower resistance, from soil with high total and soluble lead.

Conclusions:

• Soil microorganisms exhibit varied lead resistance mechanisms based on environmental lead exposure.
• Pseudomonas marginalis employs extracellular polymeric substances for lead exclusion.
• Bacillus megaterium utilizes intracellular sequestration as a lead resistance strategy, a novel finding.