Greetings,
I am currently trying to determine the toxicity of the effluents of an Electro-Fenton reactor with macrotoxicity method and colony count.
The concentrations of H2O2 I calculated (maximum 6 mg/l) is very far from the MIC reported for H2O2 against E. coli (between 469 and ~2500 mg/l).
Other components are weak organic acids and 0.2 mM of Iron.
Despite the low concentrations, I am observing a marked reduction in the colonies. Is there a chance that the prolonged interaction, even as such low concentration, between bacteria and H2O2 before plating is preventing them to create colonies?
Prolonged exposure to H2O2 is lethal to Ecoli. Free radicals damage the cell-wall. Even brief exposure can cause lethality if the catalase capacity of Escherichia is overwhelmed.
In low concentrations, cells are sensing that environment is rich in hydrogen peroxide , so it goes on stressing upon catalase machinery and spends a lot of energy in it. That explains the increased lag period.
Hydrogen peroxide effects in Escherichia coli cells. This phenomenon was observed in the wild type cells and in the xthA mutant (hypersensitive to H2O2). E.coli cells treated with low concentrations of H2O2 (micromolar) acquire resistance to different DNA damaging agents.
Hydrogen peroxide (H2O2) is a toxic oxidant that is formed inside all aerobic organisms. Escherichia coli have determined that H2O2 arises organism at a rate of 10 to 15 μM/s during growth in air-saturated glucose medium . Like virtually all forms of life, E. coli protects itself from this endogenous H2O2 through the combined actions of peroxidases and catalases, which rapidly degrade it.
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