12
Mg
Magnesium
24.305
Essential: all life
Magnesium
Major functions in cells: (1)
- Major divalent cation in all cells
- Cofactor for many reactions, including those that use NTPs (e.g. DNA and RNA synthesis).
Environmental and health impacts:
- Mg deprivation is used as part of "nutritional immunity" by mammals to restrict the growth of intracellular pathogens (2)
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(1) Magnesium: Essential for All Life
Magnesium is a major cation and is essential for life in every organism. Hundreds of enzymes require Mg to be catalytically active, including all reactions that use ATP or other nucleotides, which must bind to Mg to function. Mg is an essential cation for the synthesis of proteins due to its role generating precursors for translation, acting as a counter-ion for ATP, and neutralizing negative phosphates in DNA and RNA.
(2) Magnesium Deprivation and Nutritional Immunity
Bacteria, like all organisms, need magnesium to grow. Researchers have found that pathogenic bacteria like Salmonella that are deprived of magnesium by their host cells are unable to grow and reproduce, making magnesium deprivation an effective antibiotic technique (Cunrath and Bumann, 2019). The host cells starve the bacteria of magnesium by using a transporter called NRAMP1, which pumps magnesium out of the vesicles.
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Depletion of intrabacterial magnesium was also found to be an effective antibiotic for Mycobacterium tuberculosis, a pathogen that has developed tolerance to many previously-used antibiotic treatments (Quezada et al., 2019).
(3) Partial Substitution with Mn and Fe
There are no known cations that can completely substitute for Mg while still maintaining the structure and function of the ribosome. However, the precise nature of the counterions required for ribosomes may vary between organisms, or even in response to a changing ionic environment. For example, since life evolved in an environment with much higher ambient Fe and Mn concentrations than at present, it is possible that these ions played a more important role in ribosome function early in evolution (Bray et al., 2018). Indeed, the translation activity of E. coli ribosomes with limiting amounts of Mg can be restored by addition of Fe or Mn ions, which under these conditions can bind to levels of 500 ions per ribosome.
(3) Bacteria Reduce Ribosome Synthesis
Magnesium has several essential functions for protein synthesis, including generating precursors for translation, acting as a counter-ion for ATP, and neutralizing negative phosphates in the rRNA backbone. There are no known cations that can functionally substitute for Mg. However, bacteria do have a stress response for low Mg conditions. When there are low cytosolic Mg levels, a regulatory circuit in bacteria is able to promote the expression of Mg importers and inhibit the ATP synthase, effectively repressing synthesis of ribosomes as well. By reducing the level of ATP and ribosomes in the cell, the bacteria has more Mg ions available for translation (Pontes et al., 2016).
(4) Magnesium Limitation Promotes Biofilms
Scientists have found the magnesium limitation is an environmental trigger for bacteria to form biofilms, which is a strategy for bacterial survival (Mulcachy and Lewenza, 2011). P. aeruginosa has 3 sensors that control whether it is growing in a planktonic mode or as a biolfilm. Under magnesium limited conditions, one of these sensors, RetS, is transcriptionally repressed, which causes the bacteria to switch from the planktonic mode to aggregating as a biofilm.
(5) Plant Response to Mg Deficiency
Low magnesium leads to a decrease in crop yield. Plants have adapted a series of mechanisms to respond to magnesium limitation (Tanoi and Kobayashi, 2015).
1. Reduced transpiration
2. Accumulation of sugars/starch in source leaves
3. Alteration in redox state
4. Changes in metabolites
5. Reduced photosynthesis