Aluminium toxicity and binding to Escherichia coli

Area of Science:

• Microbiology
• Environmental Science
• Biochemistry

Background:

• Aluminium is a common environmental metal with known toxic effects.
• Understanding aluminium's interaction with bacteria like Escherichia coli is crucial for environmental and health studies.
• The speciation and bioavailability of aluminium are influenced by environmental factors such as pH.

Purpose of the Study:

• To investigate the toxicity and binding mechanisms of aluminium in Escherichia coli.
• To determine the influence of pH, iron availability, and growth phase on aluminium toxicity.
• To elucidate the cellular sites and characteristics of aluminium binding.

Main Methods:

• Bacterial growth inhibition assays at varying pH levels and iron concentrations.
• Atomic absorption spectroscopy to quantify intracellular and cell surface-bound aluminium.
• Analysis of proton displacement from cell surfaces upon aluminium exposure.

Main Results:

• Aluminium toxicity was pH-dependent, with higher sensitivity at lower pH (5.4) compared to neutral pH (6.6-6.8).
• Aluminium toxicity was exacerbated by iron omission and the use of exponential phase cultures.
• Intracellular aluminium binding occurred at a single site (Km 0.4 mM, capacity 0.13 mol (g dry wt)-1), while cell surface binding involved multiple cooperative sites.
• Aluminium exposure led to medium acidification due to proton displacement.

Conclusions:

• Aluminium toxicity in E. coli is linked to pH-dependent speciation, with Al(H2O)6(3+) likely being the active toxic species.
• Chelation of aluminium in the medium and its speciation significantly affect toxicity.
• Aluminium transport to intracellular binding sites may utilize iron (Fe(III)) transport pathways.