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Genetic Manipulation of Glycogen Allocation Affects Replicative Lifespan in E. coli.

Boehm A, Arnoldini M, Bergmiller T, Röösli T, Bigosch C, Ackermann M - PLoS Genet. (2016)

Bottom Line: We found that certain changes in the regulation of the carbohydrate metabolism can affect aging.These results demonstrate how manipulations of nutrient allocation can lead to the exclusion of the chromosome and limit replicative lifespan in E. coli, and illustrate how mutations can have phenotypic effects that are specific for cells with old poles.This raises the question how bacteria can avoid the accumulation of such mutations in their genomes over evolutionary times, and how they can achieve the long replicative lifespans that have recently been reported.

View Article: PubMed Central - PubMed

Affiliation: Biozentrum, University of Basel, Switzerland.

ABSTRACT
In bacteria, replicative aging manifests as a difference in growth or survival between the two cells emerging from division. One cell can be regarded as an aging mother with a decreased potential for future survival and division, the other as a rejuvenated daughter. Here, we aimed at investigating some of the processes involved in aging in the bacterium Escherichia coli, where the two types of cells can be distinguished by the age of their cell poles. We found that certain changes in the regulation of the carbohydrate metabolism can affect aging. A mutation in the carbon storage regulator gene, csrA, leads to a dramatically shorter replicative lifespan; csrA mutants stop dividing once their pole exceeds an age of about five divisions. These old-pole cells accumulate glycogen at their old cell poles; after their last division, they do not contain a chromosome, presumably because of spatial exclusion by the glycogen aggregates. The new-pole daughters produced by these aging mothers are born young; they only express the deleterious phenotype once their pole is old. These results demonstrate how manipulations of nutrient allocation can lead to the exclusion of the chromosome and limit replicative lifespan in E. coli, and illustrate how mutations can have phenotypic effects that are specific for cells with old poles. This raises the question how bacteria can avoid the accumulation of such mutations in their genomes over evolutionary times, and how they can achieve the long replicative lifespans that have recently been reported.

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Related in: MedlinePlus

CsrA mutant cells stop dividing at low pole ages.(A) illustrates the concept of pole age. Every cell has one pole of age zero that has been formed at the last division (the young pole), and one pole of age one or more (the older pole). We use the older pole to define individuals, and the age of the older pole to assign a pole age to each individual. A new individual emerges from division as a cell with an older pole of age 1. If this cell divides, its older pole segregates to one of the two cells emerging from division, and increases its age to two. We refer to the cell receiving this pole as the same individual that underwent division (since it has the same older pole). This individual can be referred to as the ‘mother’ of the other cell that emerges from division. This other cell—the ‘daughter’–has an older pole of age one. We refer to this other cell as a new individual. In panel A, we use colors to mark individuals. The first individual is light red, and its older pole is dark red. This individual produces two daughters, the blue individual and the green individual. (B) shows a representative lineage tree of a microcolony of csrA mutant cells. Each branching event in the lineage tree corresponds to one cell division. The lineage tree is organized according to pole age. At each cell division, the branch that represents the daughter—the cell with the new cell pole—extends to the left; the branch that represents the mother—the cell with the older pole—extends to the right. Three individuals with old poles stop dividing. Note that these experiments are initiated with single cells whose old and new pole we cannot distinguish; the branches representing the first cell division are thus dashed. In (C), we show that the cumulative probability of csrA mutant cells to stop dividing increases with increasing pole age (orange lines; see Materials and Methods for how we defined when a cell stops dividing; the median pole age at which csrA mutant cells stop dividing is 4). For wild type (purple) and csrA ΔglgA double mutant cells (green) very few cells were observed to stop dividing. Three independent experiments were performed for csrA mutant cells (N = 38, 71, 23), and two independent replicates were performed for the other two strains (N = 25, 74 for wild type, N = 31, 28 for csrA ΔglgA). (D) shows that the per division probability of csrA mutant cells to stop dividing increases with increasing pole age, for the same three experiments (denoted by different shades of orange). The diameter of the circles is proportional to the sample size at each pole age, i.e., to the number of cells that were still alive. In all three experiments, the probability to stop increases significantly with increasing pole age (logistic regression, p<0.001 for all three experiments, N = 38, 71, 23).
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pgen.1005974.g001: CsrA mutant cells stop dividing at low pole ages.(A) illustrates the concept of pole age. Every cell has one pole of age zero that has been formed at the last division (the young pole), and one pole of age one or more (the older pole). We use the older pole to define individuals, and the age of the older pole to assign a pole age to each individual. A new individual emerges from division as a cell with an older pole of age 1. If this cell divides, its older pole segregates to one of the two cells emerging from division, and increases its age to two. We refer to the cell receiving this pole as the same individual that underwent division (since it has the same older pole). This individual can be referred to as the ‘mother’ of the other cell that emerges from division. This other cell—the ‘daughter’–has an older pole of age one. We refer to this other cell as a new individual. In panel A, we use colors to mark individuals. The first individual is light red, and its older pole is dark red. This individual produces two daughters, the blue individual and the green individual. (B) shows a representative lineage tree of a microcolony of csrA mutant cells. Each branching event in the lineage tree corresponds to one cell division. The lineage tree is organized according to pole age. At each cell division, the branch that represents the daughter—the cell with the new cell pole—extends to the left; the branch that represents the mother—the cell with the older pole—extends to the right. Three individuals with old poles stop dividing. Note that these experiments are initiated with single cells whose old and new pole we cannot distinguish; the branches representing the first cell division are thus dashed. In (C), we show that the cumulative probability of csrA mutant cells to stop dividing increases with increasing pole age (orange lines; see Materials and Methods for how we defined when a cell stops dividing; the median pole age at which csrA mutant cells stop dividing is 4). For wild type (purple) and csrA ΔglgA double mutant cells (green) very few cells were observed to stop dividing. Three independent experiments were performed for csrA mutant cells (N = 38, 71, 23), and two independent replicates were performed for the other two strains (N = 25, 74 for wild type, N = 31, 28 for csrA ΔglgA). (D) shows that the per division probability of csrA mutant cells to stop dividing increases with increasing pole age, for the same three experiments (denoted by different shades of orange). The diameter of the circles is proportional to the sample size at each pole age, i.e., to the number of cells that were still alive. In all three experiments, the probability to stop increases significantly with increasing pole age (logistic regression, p<0.001 for all three experiments, N = 38, 71, 23).

Mentions: While the existence of bacterial aging is thus in line with the evolutionary theory of aging, there is a puzzling quantitative discrepancy between expectation and observation: bacteria live much longer than a simple theoretical consideration would suggest. Two studies—one with Caulobacter crescentus [1], the other with E. coli [6]–followed single cells for long times, and reported that individual bacterial cells can survive and divide for more than one hundred divisions. The observation with E. coli is particularly surprising, as can be shown with a simple argument: in bacterial populations where cells with different pole ages are exposed to the same external conditions, the distribution of pole ages is exponential: 50% of the cells have a pole of age one, 25% have a pole of age two, and so on (for a definition of the pole age of a bacterial cell see Fig 1A). More formally, the fraction of cells with a pole age n is 2-n; i.e. only about one in a million cells has a pole age of 20 or more. Therefore, there is virtually no selection for cells to remain viable once their cell pole is 40 or 50 divisions old (this argument assumes that the process of aging in this case depends on replicative rather than chronological age). Importantly, the pole age distribution in a bacterial population in which all cells are exposed to the same external conditions and extrinsic mortality is stable and not dependent on the growth dynamics of the population [9,10].


Genetic Manipulation of Glycogen Allocation Affects Replicative Lifespan in E. coli.

Boehm A, Arnoldini M, Bergmiller T, Röösli T, Bigosch C, Ackermann M - PLoS Genet. (2016)

CsrA mutant cells stop dividing at low pole ages.(A) illustrates the concept of pole age. Every cell has one pole of age zero that has been formed at the last division (the young pole), and one pole of age one or more (the older pole). We use the older pole to define individuals, and the age of the older pole to assign a pole age to each individual. A new individual emerges from division as a cell with an older pole of age 1. If this cell divides, its older pole segregates to one of the two cells emerging from division, and increases its age to two. We refer to the cell receiving this pole as the same individual that underwent division (since it has the same older pole). This individual can be referred to as the ‘mother’ of the other cell that emerges from division. This other cell—the ‘daughter’–has an older pole of age one. We refer to this other cell as a new individual. In panel A, we use colors to mark individuals. The first individual is light red, and its older pole is dark red. This individual produces two daughters, the blue individual and the green individual. (B) shows a representative lineage tree of a microcolony of csrA mutant cells. Each branching event in the lineage tree corresponds to one cell division. The lineage tree is organized according to pole age. At each cell division, the branch that represents the daughter—the cell with the new cell pole—extends to the left; the branch that represents the mother—the cell with the older pole—extends to the right. Three individuals with old poles stop dividing. Note that these experiments are initiated with single cells whose old and new pole we cannot distinguish; the branches representing the first cell division are thus dashed. In (C), we show that the cumulative probability of csrA mutant cells to stop dividing increases with increasing pole age (orange lines; see Materials and Methods for how we defined when a cell stops dividing; the median pole age at which csrA mutant cells stop dividing is 4). For wild type (purple) and csrA ΔglgA double mutant cells (green) very few cells were observed to stop dividing. Three independent experiments were performed for csrA mutant cells (N = 38, 71, 23), and two independent replicates were performed for the other two strains (N = 25, 74 for wild type, N = 31, 28 for csrA ΔglgA). (D) shows that the per division probability of csrA mutant cells to stop dividing increases with increasing pole age, for the same three experiments (denoted by different shades of orange). The diameter of the circles is proportional to the sample size at each pole age, i.e., to the number of cells that were still alive. In all three experiments, the probability to stop increases significantly with increasing pole age (logistic regression, p<0.001 for all three experiments, N = 38, 71, 23).
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4836754&req=5

pgen.1005974.g001: CsrA mutant cells stop dividing at low pole ages.(A) illustrates the concept of pole age. Every cell has one pole of age zero that has been formed at the last division (the young pole), and one pole of age one or more (the older pole). We use the older pole to define individuals, and the age of the older pole to assign a pole age to each individual. A new individual emerges from division as a cell with an older pole of age 1. If this cell divides, its older pole segregates to one of the two cells emerging from division, and increases its age to two. We refer to the cell receiving this pole as the same individual that underwent division (since it has the same older pole). This individual can be referred to as the ‘mother’ of the other cell that emerges from division. This other cell—the ‘daughter’–has an older pole of age one. We refer to this other cell as a new individual. In panel A, we use colors to mark individuals. The first individual is light red, and its older pole is dark red. This individual produces two daughters, the blue individual and the green individual. (B) shows a representative lineage tree of a microcolony of csrA mutant cells. Each branching event in the lineage tree corresponds to one cell division. The lineage tree is organized according to pole age. At each cell division, the branch that represents the daughter—the cell with the new cell pole—extends to the left; the branch that represents the mother—the cell with the older pole—extends to the right. Three individuals with old poles stop dividing. Note that these experiments are initiated with single cells whose old and new pole we cannot distinguish; the branches representing the first cell division are thus dashed. In (C), we show that the cumulative probability of csrA mutant cells to stop dividing increases with increasing pole age (orange lines; see Materials and Methods for how we defined when a cell stops dividing; the median pole age at which csrA mutant cells stop dividing is 4). For wild type (purple) and csrA ΔglgA double mutant cells (green) very few cells were observed to stop dividing. Three independent experiments were performed for csrA mutant cells (N = 38, 71, 23), and two independent replicates were performed for the other two strains (N = 25, 74 for wild type, N = 31, 28 for csrA ΔglgA). (D) shows that the per division probability of csrA mutant cells to stop dividing increases with increasing pole age, for the same three experiments (denoted by different shades of orange). The diameter of the circles is proportional to the sample size at each pole age, i.e., to the number of cells that were still alive. In all three experiments, the probability to stop increases significantly with increasing pole age (logistic regression, p<0.001 for all three experiments, N = 38, 71, 23).
Mentions: While the existence of bacterial aging is thus in line with the evolutionary theory of aging, there is a puzzling quantitative discrepancy between expectation and observation: bacteria live much longer than a simple theoretical consideration would suggest. Two studies—one with Caulobacter crescentus [1], the other with E. coli [6]–followed single cells for long times, and reported that individual bacterial cells can survive and divide for more than one hundred divisions. The observation with E. coli is particularly surprising, as can be shown with a simple argument: in bacterial populations where cells with different pole ages are exposed to the same external conditions, the distribution of pole ages is exponential: 50% of the cells have a pole of age one, 25% have a pole of age two, and so on (for a definition of the pole age of a bacterial cell see Fig 1A). More formally, the fraction of cells with a pole age n is 2-n; i.e. only about one in a million cells has a pole age of 20 or more. Therefore, there is virtually no selection for cells to remain viable once their cell pole is 40 or 50 divisions old (this argument assumes that the process of aging in this case depends on replicative rather than chronological age). Importantly, the pole age distribution in a bacterial population in which all cells are exposed to the same external conditions and extrinsic mortality is stable and not dependent on the growth dynamics of the population [9,10].

Bottom Line: We found that certain changes in the regulation of the carbohydrate metabolism can affect aging.These results demonstrate how manipulations of nutrient allocation can lead to the exclusion of the chromosome and limit replicative lifespan in E. coli, and illustrate how mutations can have phenotypic effects that are specific for cells with old poles.This raises the question how bacteria can avoid the accumulation of such mutations in their genomes over evolutionary times, and how they can achieve the long replicative lifespans that have recently been reported.

View Article: PubMed Central - PubMed

Affiliation: Biozentrum, University of Basel, Switzerland.

ABSTRACT
In bacteria, replicative aging manifests as a difference in growth or survival between the two cells emerging from division. One cell can be regarded as an aging mother with a decreased potential for future survival and division, the other as a rejuvenated daughter. Here, we aimed at investigating some of the processes involved in aging in the bacterium Escherichia coli, where the two types of cells can be distinguished by the age of their cell poles. We found that certain changes in the regulation of the carbohydrate metabolism can affect aging. A mutation in the carbon storage regulator gene, csrA, leads to a dramatically shorter replicative lifespan; csrA mutants stop dividing once their pole exceeds an age of about five divisions. These old-pole cells accumulate glycogen at their old cell poles; after their last division, they do not contain a chromosome, presumably because of spatial exclusion by the glycogen aggregates. The new-pole daughters produced by these aging mothers are born young; they only express the deleterious phenotype once their pole is old. These results demonstrate how manipulations of nutrient allocation can lead to the exclusion of the chromosome and limit replicative lifespan in E. coli, and illustrate how mutations can have phenotypic effects that are specific for cells with old poles. This raises the question how bacteria can avoid the accumulation of such mutations in their genomes over evolutionary times, and how they can achieve the long replicative lifespans that have recently been reported.

Show MeSH
Related in: MedlinePlus