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Alteration of Streptococcus pneumoniae membrane properties by the folate analog methotrexate
Abstract:
The antifolate compound methotrexate (MTX) is toxic to the gram-positive bacterium Streptococcus pneumoniae. Interaction of MTX with this bacterium resulted in an increase in the electric transmembrane potential (delta psi) and enhanced the delta psi-dependent uptake of isoleucine and MTX. In contrast, delta psi-independent uptake of glutamine was not changed. Folate, a nontoxic analog of MTX, did not exhibit these membrane effects, nor did it prevent the effect of MTX, suggesting that the NH2 in position 4 of the pteridine ring of the MTX molecule is involved in the MTX response. A strain bearing the nonsense mutation amiA9, selected for MTX resistance, did not exhibit increased membrane potential after MTX pretreatment. This suggests that MTX interacts with a specific membrane component in S. pneumoniae. A resulting change in ion permeability could lead to changes in the magnitude of the delta psi. The MTX-sensitive component is altered or absent in mutant amiA9.
Insights
Methotrexate (MTX) disrupts Streptococcus pneumoniae by increasing electric transmembrane potential (delta psi), affecting nutrient uptake. A specific membrane component, altered in resistant strains, mediates this MTX interaction.
Area of Science:
- Microbiology
- Bacterial Physiology
- Membrane Transport
Background:
- Methotrexate (MTX) is an antifolate compound known for its toxicity to bacteria.
- Streptococcus pneumoniae is a significant human pathogen, and understanding its response to antimicrobial agents is crucial.
Purpose of the Study:
- To investigate the mechanism of methotrexate (MTX) toxicity in Streptococcus pneumoniae.
- To elucidate the role of the electric transmembrane potential (delta psi) in MTX's effect on bacterial cells.
Main Methods:
- Exposure of Streptococcus pneumoniae to MTX and folate.
- Measurement of electric transmembrane potential (delta psi).
- Analysis of nutrient (isoleucine, glutamine) uptake.
- Comparison with an MTX-resistant mutant (amiA9).
Main Results:
- MTX treatment increased delta psi in S. pneumoniae.
- MTX enhanced delta psi-dependent uptake of isoleucine and MTX itself.
- Delta psi-independent glutamine uptake remained unchanged.
- Folate did not induce these membrane effects.
- An MTX-resistant mutant (amiA9) showed no increase in delta psi upon MTX exposure.
Conclusions:
- MTX interacts with a specific membrane component in S. pneumoniae, leading to altered ion permeability and increased delta psi.
- This interaction is crucial for MTX's toxic effects and nutrient uptake modulation.
- The identified MTX-sensitive component is absent or altered in the amiA9 mutant, explaining MTX resistance.