Redox potential-dependent nitrite metabolism by Salmonella typhimurium

Area of Science:

• Microbiology
• Bacterial Physiology
• Food Safety

Background:

• Salmonellae exhibit resistance to sodium nitrite (NaNO2), a common food preservative.
• The mechanism of NaNO2 resistance and its interaction with bacterial cells requires further elucidation.

Purpose of the Study:

• To investigate the interaction between Salmonella typhimurium and sodium nitrite (NaNO2).
• To determine if lipopolysaccharide (LPS) plays a role in NaNO2 resistance.
• To explore the conditions and mechanisms underlying NaNO2 metabolism by Salmonella.

Main Methods:

• Salmonella typhimurium growth experiments with NaNO2.
• Ethylenediaminetetraacetic acid (EDTA) pretreatment to remove lipopolysaccharide.
• Monitoring of NaNO2 concentration in culture media under varying pH and redox potentials.
• Cell-free system experiments with heat-treated and untreated cell suspensions.

Main Results:

• Lipopolysaccharide removal did not affect NaNO2 inhibition, indicating it's not involved in exclusion.
• NaNO2 disappeared during Salmonella growth, with losses ceasing in stationary phase unless pH > 7.0.
• NaNO2 loss occurred in cell-free systems at specific redox potentials (-250 to -175 mV).
• Heat treatment of cells abolished NaNO2 loss, irrespective of redox potential.

Conclusions:

• Salmonella typhimurium can metabolize sodium nitrite (NaNO2).
• This metabolism is likely mediated by a redox-controlled nitrite-reducing enzyme.
• Lipopolysaccharide is not responsible for excluding NaNO2 from Salmonella cells.