Exposure to the Proton Scavenger Glycine under Alkaline Conditions Induces Escherichia coli Viability Loss

Abstract

Our previous work described a clear loss of Escherichia coli (E. coli) membrane integrity after incubation with glycine or its N-methylated derivatives N-methylglycine (sarcosine) and N,N-dimethylglycine (DMG), but not N,N,N-trimethylglycine (betaine), under alkaline stress conditions. The current study offers a thorough viability analysis, based on a combination of real-time physiological techniques, of E. coli exposed to glycine and its N-methylated derivatives at alkaline pH. Flow cytometry was applied to assess various physiological parameters such as membrane permeability, esterase activity, respiratory activity and membrane potential. ATP and inorganic phosphate concentrations were also determined. Membrane damage was confirmed through the measurement of nucleic acid leakage. Results further showed no loss of esterase or respiratory activity, while an instant and significant decrease in the ATP concentration occurred upon exposure to either glycine, sarcosine or DMG, but not betaine. There was a clear membrane hyperpolarization as well as a significant increase in cellular inorganic phosphate concentration. Based on these results, we suggest that the inability to sustain an adequate level of ATP combined with a decrease in membrane functionality leads to the loss of bacterial viability when exposed to the proton scavengers glycine, sarcosine and DMG at alkaline pH.

Bicarbonate Inhibits Bacterial Growth and Biofilm Formation of Prevalent Cystic Fibrosis Pathogens

“…Alkaline conditions may alter cytosolic pH of bacteria when protons must be taken up from the extracellular medium. Under alkaline conditions proton scavengers markedly decrease E. coli viability ( Vanhauteghem et al, 2013 ). This phenomenon can be explained by partitioning of unprotonated scavengers into the cytosol where they become protonated and increase cytosolic pH.…”

Hydrophobic residues are critical for the helix-forming, hemolytic and bactericidal activities of amphipathic antimicrobial peptide TP4

“…aeruginosa treated by the bactericide granulysin [ 11 ] ( Fig 1B and 1C ). Although depolarization of membrane potential is considered to be an initial event in membrane injury, hyperpolarization has also been reported to be an adaptive behavior before cell death pathways are triggered [ 36 – 38 ]. Therefore, it is implicated that the treatment of AMPs at a sub-lethal dose may enable the bacteria to trigger an adaption pathway and develop drug-resistant mechanisms.…”

Sarkosyl-Induced Helical Structure of an Antimicrobial Peptide GW-Q6 Plays an Essential Role in the Binding of Surface Receptor OprI in Pseudomonas aeruginosa

“…Although depolarization of membrane potential is considered to be an initial event of membrane injury, hyperpolarization is reported as an adaptation prior to bacterial cell death or full recovery depending on the concentration of peptides employed [ 48 , 49 ]. Hyperpolarization has also been associated with the formation of superoxide radicals which are involved in membrane integrity and cell viability [ 48 , 50 ].…”