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Enhancement of cell death due to decrease in Mg2+ uptake by OmpC (cation-selective porin) deficiency in ribosome
A Apirakaramwong1, J Fukuchi, K Kashiwagi
1Faculty of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, 263-8522, Japan.
Abstract:
Ribosome modulation factor (RMF) is involved in stabilization of ribosomes during the transition from exponential growth to the stationary growth phase in Escherichia coli. A deficiency of RMF is known to reduce cell viability. Overaccumulation of spermidine also leads to a decrease in cell viability and to a decrease in the synthesis of RMF and of the cation-selective porin OmpC. Thus, a decrease in RMF levels may be involved in the decreased cell viability caused by excess spermidine. Because spermidine also influences the expression of OmpC, we examined whether OmpC deficiency enhances the cell death caused by RMF deficiency. The ompC mutant by itself did not affect protein synthesis or cell viability, but the double rmf ompC mutant produced a much larger decrease in protein synthesis and cell viability than did the single rmf mutant. There was also a decrease in the amount of ribosomes and in the Mg2+ content in the double rmf ompC mutant, and cell viability could be partially restored by the addition of Mg2+ to the growth medium. RMF deficiency was found to inhibit the synthesis of another cation-selective porin OmpF. Thus, the double rmf ompC mutant is deficient in both OmpC and OmpF, which probably accounts for the pronounced decrease in Mg2+ uptake in this mutant. The results indicate that both RMF and Mg2+, acting through stabilization of ribosomes, are important for cell viability at the stationary growth phase.
Insights
Ribosome modulation factor (RMF) and magnesium (Mg2+) stabilize ribosomes, crucial for E. coli viability in stationary phase. RMF deficiency combined with OmpC porin deficiency severely impairs cell viability and protein synthesis.
Area of Science:
- Microbiology
- Molecular Biology
- Cell Biology
Background:
- Ribosome modulation factor (RMF) stabilizes ribosomes during growth phase transitions in Escherichia coli.
- RMF deficiency reduces cell viability, while spermidine overaccumulation decreases both viability and RMF/OmpC synthesis.
Purpose of the Study:
- To investigate if OmpC porin deficiency exacerbates cell death caused by RMF deficiency.
- To understand the role of RMF, OmpC, and Mg2+ in maintaining cell viability during stationary phase.
Main Methods:
- Comparative analysis of single (rmf, ompC) and double (rmf ompC) mutants in Escherichia coli.
- Assessment of protein synthesis, cell viability, ribosome content, and Mg2+ levels.
- Evaluation of OmpF porin synthesis in RMF-deficient strains.
Main Results:
- The double rmf ompC mutant showed significantly reduced protein synthesis and cell viability compared to the single rmf mutant.
- A decrease in ribosome content and Mg2+ was observed in the double mutant, with partial viability restoration upon Mg2+ addition.
- RMF deficiency inhibited OmpF synthesis, leading to a combined deficiency of OmpC and OmpF in the double mutant, impacting Mg2+ uptake.
Conclusions:
- Both RMF and Mg2+ are vital for stabilizing ribosomes and ensuring cell viability in the stationary growth phase.
- The combined deficiency of OmpC and OmpF porins, alongside RMF deficiency, severely compromises cell viability due to impaired Mg2+ uptake.
- Ribosome stabilization is a key mechanism underlying the importance of RMF and Mg2+ for stationary phase survival.