Free spermidine evokes superoxide radicals that manifest toxicity
- CSIR Institute of Microbial Technology, India
- St John's Medical College Hospital, India
Abstract
Spermidine and other polyamines alleviate oxidative stress, yet excess spermidine seems toxic to Escherichia coli unless it is neutralized by SpeG, an enzyme for the spermidine N-acetyl transferase function. Thus, wild-type E. coli can tolerate applied exogenous spermidine stress, but DspeG strain of E. coli fails to do that. Here, using different ROS probes and performing electron paramagnetic resonance spectroscopy, we provide evidence that although spermidine mitigates oxidative stress by lowering overall ROS levels, excess of it simultaneously triggers the production of superoxide radicals, thereby causing toxicity in the DspeG strain. Furthermore, performing microarray experiment and other biochemical assays, we show that the spermidine-induced superoxide anions affected redox balance and iron homeostasis. Finally, we demonstrate that while RNA-bound spermidine inhibits iron oxidation, free spermidine interacts and oxidizes the iron to evoke superoxide radicals directly. Therefore, we propose that the spermidine-induced superoxide generation is one of the major causes of spermidine toxicity in E. coli.
Data availability
Microarray data is available in the GEO server. GEO accession Number GSE154618 has been provided in the material and method section.Source files for the following Figures were provided as a zip folder:Figure 1A, 1B, 1C, 1FFigure 2Figure 3A, 3B, 3C, 3D, 3E, 3F, 3GFigure 4B (ii), 4C, 4D, 4EFigure 5A, 5B, 5DFigure 6D, 6E, 6GFigure 1-figure supplement 1C
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The global transcriptomic profile in the spermidine-stressed E. coliNCBI Gene Expression Omnibus, GSE154618.
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Funding
Council of Scientific and Industrial Research, India (MLP042)
- Dipak Dutta
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2022, Kumar et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Free spermidine evokes superoxide radicals that manifest toxicity
eLife 11:e77704.
https://doi.org/10.7554/eLife.77704
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