Magnesium modulates Bacillus subtilis cell division frequency
This article has been Reviewed by the following groups
Listed in
- Evaluated articles (Arcadia Science)
Abstract
By chance, we discovered a window of extracellular magnesium (Mg 2+ ) availability that modulates Bacillus subtilis division frequency without affecting growth rate. In this window, cells grown with excess Mg 2+ produce shorter cells than those grown in unsupplemented medium. The Mg 2+ -responsive adjustment in cell length occurs in both rich and minimal media and in domesticated and undomesticated strains. Of other divalent cations tested, manganese (Mn 2+ ) and zinc (Zn 2+ ) also resulted in cell shortening, but only at concentrations that affected growth. Cell length decreased proportionally with increasing Mg 2+ from 0.2 mM to 2.0 mM, with little or no detectable change in labile, intracellular Mg 2+ based on a riboswitch reporter. Cells grown in excess Mg 2+ had fewer nucleoids and possessed more FtsZ-rings per unit cell length, consistent with increased division frequency. Remarkably, when shifting cells from unsupplemented to supplemented medium, more than half of the cell length decrease occurred in the first 10 min, consistent with rapid division onset. Relative to unsupplemented cells, cells growing at steady-state with excess Mg 2+ showed enhanced expression of a large number of SigB-regulated genes and activation of the Fur, MntR, and Zur regulons. Thus, by manipulating the availability of one nutrient, we were able to uncouple growth rate from division frequency and identify transcriptional changes suggesting cell division is accompanied by oxidative stress and an enhanced demand to sequester and/or increase uptake of iron, Mn 2+ , and Zn 2+ .
IMPORTANCE
The signals cells use to trigger cell division are unknown. Although division is often considered intrinsic to the cell-cycle, microorganisms can continue to grow and repeat rounds of DNA replication without dividing, indicating cycles of division can be skipped. Here we show that by manipulating a single nutrient, Mg 2+ , cell division can be uncoupled from growth rate. This finding can be applied to investigate the nature of the cell division signal(s).
Article activity feed
-
General comments:
This study carefully delineates the role of magnesium in cell division versus cell elongation. The results are really important specifically for rod-shaped bacteria and also an important contribution to the broader field of understanding cell shape. Specifically, I love that they are distinguishing between labile and non-labile intracellular magnesium pools, as well as extracellular magnesium! These three pools are really challenging to separate but I commend them on engaging with this topic and using it to provide alternative explanations for their observations!
A major contribution to prior findings on the effects of magnesium is the author’s ability to visualize the number of septa in the elongating cells in the absence of magnesium. This is novel information and I think the field will benefit from the microscopy …
General comments:
This study carefully delineates the role of magnesium in cell division versus cell elongation. The results are really important specifically for rod-shaped bacteria and also an important contribution to the broader field of understanding cell shape. Specifically, I love that they are distinguishing between labile and non-labile intracellular magnesium pools, as well as extracellular magnesium! These three pools are really challenging to separate but I commend them on engaging with this topic and using it to provide alternative explanations for their observations!
A major contribution to prior findings on the effects of magnesium is the author’s ability to visualize the number of septa in the elongating cells in the absence of magnesium. This is novel information and I think the field will benefit from the microscopy data shown here.
I completely agree with the authors that we need to be more careful when using rich media such as LB. It is particularly sad that we may be missing really interesting biology because of that! It’s worth moving away from such media or at least being more careful about batch to batch variability. Batch to batch variability is not as well appreciated in microbiology as it is for growing other cell types (for example, mammalian cells and insect cells).
For me, the most exciting finding was that a large part of the cell length changes within the first 10min after adding magnesium. The authors do speculate in the discussion that this is likely happening because of biophysical or enzymatic effects, and I hope they explore this further in the future!
I love how the paper reads like a novel! Congratulations on a very well-written paper!
Kudos to the authors for providing many alternative explanations for their results. It demonstrates critical thinking and an open-mind to finding the truth.
Specific comments:
Figure 2C → please include indication of statistical significance
Figure 3C → please include indication of statistical significance
Figure 6A → please include indication of statistical significance
Figure 8B → please include indication of statistical significance
Figure S1B → please include indication of statistical significance
Figure S3B → please include indication of statistical significance
For your overexpression experiments, do the overexpressed proteins have a tag? It would be helpful to have Western blot data showing that the particular proteins are actually being overexpressed. I think the phenotypes that you observe are very compelling so I don’t doubt the conclusions. Western blot data would just provide some additional confirmation that you are actually achieving overexpression of UppS, MraY, and BcrC.
Questions:
Based on your data, there are definitely differences in gene expression when you compare cells grown in media with and without magnesium. Because the majority in cell length increase occurs in such a short time though (the first 10min), I was wondering if you think that some or most of it is not due to gene expression? Do you have any hypotheses what is most likely to be affected by magnesium? Do you think if the membrane may be affected?
Why do you think less magnesium activates this program of less division and more elongation? Additionally why is abundant magnesium activating a program of increased cell division and less elongation? Do you think there is some evolutionary advantage, especially considering how important magnesium is for ATP production?
Related to this previous question, I also wonder if this magnesium-dependent phenotype would extend to other unicellular organisms, may be protists or algae? That would be a really exciting direction to explore!
Regarding the zinc and manganese experiments, why do you think they lead to additional phenotypes compared to magnesium? Do you have any hypotheses?
Regarding your results that Lipid I availability may be a major a problem for the cell division in the absence of magnesium, do you think that is due to effects magnesium has on the enzymes directly, or do you think magnesium affects the substrate availability/conformation by coordinating the phosphate groups? Or something else, may be membrane conformation?
-
General comments:
This study carefully delineates the role of magnesium in cell division versus cell elongation. The results are really important specifically for rod-shaped bacteria and also an important contribution to the broader field of understanding cell shape. Specifically, I love that they are distinguishing between labile and non-labile intracellular magnesium pools, as well as extracellular magnesium! These three pools are really challenging to separate but I commend them on engaging with this topic and using it to provide alternative explanations for their observations!
A major contribution to prior findings on the effects of magnesium is the author’s ability to visualize the number of septa in the elongating cells in the absence of magnesium. This is novel information and I think the field will benefit from the microscopy …
General comments:
This study carefully delineates the role of magnesium in cell division versus cell elongation. The results are really important specifically for rod-shaped bacteria and also an important contribution to the broader field of understanding cell shape. Specifically, I love that they are distinguishing between labile and non-labile intracellular magnesium pools, as well as extracellular magnesium! These three pools are really challenging to separate but I commend them on engaging with this topic and using it to provide alternative explanations for their observations!
A major contribution to prior findings on the effects of magnesium is the author’s ability to visualize the number of septa in the elongating cells in the absence of magnesium. This is novel information and I think the field will benefit from the microscopy data shown here.
I completely agree with the authors that we need to be more careful when using rich media such as LB. It is particularly sad that we may be missing really interesting biology because of that! It’s worth moving away from such media or at least being more careful about batch to batch variability. Batch to batch variability is not as well appreciated in microbiology as it is for growing other cell types (for example, mammalian cells and insect cells).
For me, the most exciting finding was that a large part of the cell length changes within the first 10min after adding magnesium. The authors do speculate in the discussion that this is likely happening because of biophysical or enzymatic effects, and I hope they explore this further in the future!
I love how the paper reads like a novel! Congratulations on a very well-written paper!
Kudos to the authors for providing many alternative explanations for their results. It demonstrates critical thinking and an open-mind to finding the truth.
Specific comments:
Figure 2C → please include indication of statistical significance
Figure 3C → please include indication of statistical significance
Figure 6A → please include indication of statistical significance
Figure 8B → please include indication of statistical significance
Figure S1B → please include indication of statistical significance
Figure S3B → please include indication of statistical significance
For your overexpression experiments, do the overexpressed proteins have a tag? It would be helpful to have Western blot data showing that the particular proteins are actually being overexpressed. I think the phenotypes that you observe are very compelling so I don’t doubt the conclusions. Western blot data would just provide some additional confirmation that you are actually achieving overexpression of UppS, MraY, and BcrC.
Questions:
Based on your data, there are definitely differences in gene expression when you compare cells grown in media with and without magnesium. Because the majority in cell length increase occurs in such a short time though (the first 10min), I was wondering if you think that some or most of it is not due to gene expression? Do you have any hypotheses what is most likely to be affected by magnesium? Do you think if the membrane may be affected?
Why do you think less magnesium activates this program of less division and more elongation? Additionally why is abundant magnesium activating a program of increased cell division and less elongation? Do you think there is some evolutionary advantage, especially considering how important magnesium is for ATP production?
Related to this previous question, I also wonder if this magnesium-dependent phenotype would extend to other unicellular organisms, may be protists or algae? That would be a really exciting direction to explore!
Regarding the zinc and manganese experiments, why do you think they lead to additional phenotypes compared to magnesium? Do you have any hypotheses?
Regarding your results that Lipid I availability may be a major a problem for the cell division in the absence of magnesium, do you think that is due to effects magnesium has on the enzymes directly, or do you think magnesium affects the substrate availability/conformation by coordinating the phosphate groups? Or something else, may be membrane conformation?
-
