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Metabolic co-dependence gives rise to collective oscillations within biofilms.

Liu J, Prindle A, Humphries J, Gabalda-Sagarra M, Asally M, Lee DY, Ly S, Garcia-Ojalvo J, Süel GM - Nature (2015)

Bottom Line: It remains unclear how these opposing interactions are resolved at the population level.We discover that this conflict between protection and starvation is resolved through emergence of long-range metabolic co-dependence between peripheral and interior cells.As a result, biofilm growth halts periodically, increasing nutrient availability for the sheltered interior cells.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, University of California San Diego, California 92093, USA.

ABSTRACT
Cells that reside within a community can cooperate and also compete with each other for resources. It remains unclear how these opposing interactions are resolved at the population level. Here we investigate such an internal conflict within a microbial (Bacillus subtilis) biofilm community: cells in the biofilm periphery not only protect interior cells from external attack but also starve them through nutrient consumption. We discover that this conflict between protection and starvation is resolved through emergence of long-range metabolic co-dependence between peripheral and interior cells. As a result, biofilm growth halts periodically, increasing nutrient availability for the sheltered interior cells. We show that this collective oscillation in biofilm growth benefits the community in the event of a chemical attack. These findings indicate that oscillations support population-level conflict resolution by coordinating competing metabolic demands in space and time, suggesting new strategies to control biofilm growth.

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Metabolic codependence between interior and peripheral cells gives rise to oscillations that make the colony more resilient to external attack. a, Visual representation of the predicted outcome of an external attack on biofilm growth. b, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a wild type biofilm region shows cell death with and without challenge by 2% w/w H2O2. Scale bar represents 50 µm. c, In the same biofilm, difference images (white regions indicate cell growth) show wild type growth with and without challenge by H2O2. d, Overexpression of glutamate dehydrogenase (GDH, pink) promotes more production of ammonium from glutamate. e, Experimental (top) and modeling results (bottom) of GDH overexpression (induced with 1 mM IPTG, indicated by pink shading). f, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a colony overexpressing GDH with and without challenge by H2O2. g, In the same biofilm, difference images show cell growth during GDH overexpression alone, and with challenge by H2O2. h, Quantification of total biofilm growth rate in wild type (upper, n = 4 colonies) and GDH overexpression (lower, n = 3 colonies) strains upon challenge with H2O2. Error bars represent standard deviations. Modeling data are shown as an inset for each strain. i, Codependence between interior and peripheral cells exhibited in a wild type strain results in a growth strategy that sustains the viability of interior cells, while independence enforced by a GDH overexpression strain results in starvation of interior cells and reduced resilience to external attack.
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Figure 4: Metabolic codependence between interior and peripheral cells gives rise to oscillations that make the colony more resilient to external attack. a, Visual representation of the predicted outcome of an external attack on biofilm growth. b, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a wild type biofilm region shows cell death with and without challenge by 2% w/w H2O2. Scale bar represents 50 µm. c, In the same biofilm, difference images (white regions indicate cell growth) show wild type growth with and without challenge by H2O2. d, Overexpression of glutamate dehydrogenase (GDH, pink) promotes more production of ammonium from glutamate. e, Experimental (top) and modeling results (bottom) of GDH overexpression (induced with 1 mM IPTG, indicated by pink shading). f, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a colony overexpressing GDH with and without challenge by H2O2. g, In the same biofilm, difference images show cell growth during GDH overexpression alone, and with challenge by H2O2. h, Quantification of total biofilm growth rate in wild type (upper, n = 4 colonies) and GDH overexpression (lower, n = 3 colonies) strains upon challenge with H2O2. Error bars represent standard deviations. Modeling data are shown as an inset for each strain. i, Codependence between interior and peripheral cells exhibited in a wild type strain results in a growth strategy that sustains the viability of interior cells, while independence enforced by a GDH overexpression strain results in starvation of interior cells and reduced resilience to external attack.

Mentions: The metabolic codependence between interior and peripheral cells gives rise to the surprising prediction that external attack could promote growth within the biofilm. Specifically, killing of peripheral cells will eliminate their glutamate consumption, which will increase glutamate availability in the biofilm and thereby promote growth of interior cells (Fig. 4a). To test this hypothesis, we measured cell death and growth within oscillating biofilms (Fig. 4b, top and Extended Data Fig. 7). When we exposed the biofilm to media containing hydrogen peroxide (H2O2), we observed increased cell death predominantly in the biofilm periphery (Fig. 4b, bottom and Extended Data Fig. 8). As predicted, death of peripheral cells led to growth of interior cells (Fig. 4c and Extended Data Fig. 8). To verify that this response is not uniquely triggered by H2O2, we exposed biofilms to the antibiotic chloramphenicol and again observed growth of interior cells (Extended Data Fig. 8). These findings further support our hypothesis that glutamate consumption by peripheral cells limits its availability in the biofilm.


Metabolic co-dependence gives rise to collective oscillations within biofilms.

Liu J, Prindle A, Humphries J, Gabalda-Sagarra M, Asally M, Lee DY, Ly S, Garcia-Ojalvo J, Süel GM - Nature (2015)

Metabolic codependence between interior and peripheral cells gives rise to oscillations that make the colony more resilient to external attack. a, Visual representation of the predicted outcome of an external attack on biofilm growth. b, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a wild type biofilm region shows cell death with and without challenge by 2% w/w H2O2. Scale bar represents 50 µm. c, In the same biofilm, difference images (white regions indicate cell growth) show wild type growth with and without challenge by H2O2. d, Overexpression of glutamate dehydrogenase (GDH, pink) promotes more production of ammonium from glutamate. e, Experimental (top) and modeling results (bottom) of GDH overexpression (induced with 1 mM IPTG, indicated by pink shading). f, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a colony overexpressing GDH with and without challenge by H2O2. g, In the same biofilm, difference images show cell growth during GDH overexpression alone, and with challenge by H2O2. h, Quantification of total biofilm growth rate in wild type (upper, n = 4 colonies) and GDH overexpression (lower, n = 3 colonies) strains upon challenge with H2O2. Error bars represent standard deviations. Modeling data are shown as an inset for each strain. i, Codependence between interior and peripheral cells exhibited in a wild type strain results in a growth strategy that sustains the viability of interior cells, while independence enforced by a GDH overexpression strain results in starvation of interior cells and reduced resilience to external attack.
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Related In: Results  -  Collection

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Show All Figures
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Figure 4: Metabolic codependence between interior and peripheral cells gives rise to oscillations that make the colony more resilient to external attack. a, Visual representation of the predicted outcome of an external attack on biofilm growth. b, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a wild type biofilm region shows cell death with and without challenge by 2% w/w H2O2. Scale bar represents 50 µm. c, In the same biofilm, difference images (white regions indicate cell growth) show wild type growth with and without challenge by H2O2. d, Overexpression of glutamate dehydrogenase (GDH, pink) promotes more production of ammonium from glutamate. e, Experimental (top) and modeling results (bottom) of GDH overexpression (induced with 1 mM IPTG, indicated by pink shading). f, Phase contrast merged with cell death marker (cyan, 1 µM Sytox Green) images of a colony overexpressing GDH with and without challenge by H2O2. g, In the same biofilm, difference images show cell growth during GDH overexpression alone, and with challenge by H2O2. h, Quantification of total biofilm growth rate in wild type (upper, n = 4 colonies) and GDH overexpression (lower, n = 3 colonies) strains upon challenge with H2O2. Error bars represent standard deviations. Modeling data are shown as an inset for each strain. i, Codependence between interior and peripheral cells exhibited in a wild type strain results in a growth strategy that sustains the viability of interior cells, while independence enforced by a GDH overexpression strain results in starvation of interior cells and reduced resilience to external attack.
Mentions: The metabolic codependence between interior and peripheral cells gives rise to the surprising prediction that external attack could promote growth within the biofilm. Specifically, killing of peripheral cells will eliminate their glutamate consumption, which will increase glutamate availability in the biofilm and thereby promote growth of interior cells (Fig. 4a). To test this hypothesis, we measured cell death and growth within oscillating biofilms (Fig. 4b, top and Extended Data Fig. 7). When we exposed the biofilm to media containing hydrogen peroxide (H2O2), we observed increased cell death predominantly in the biofilm periphery (Fig. 4b, bottom and Extended Data Fig. 8). As predicted, death of peripheral cells led to growth of interior cells (Fig. 4c and Extended Data Fig. 8). To verify that this response is not uniquely triggered by H2O2, we exposed biofilms to the antibiotic chloramphenicol and again observed growth of interior cells (Extended Data Fig. 8). These findings further support our hypothesis that glutamate consumption by peripheral cells limits its availability in the biofilm.

Bottom Line: It remains unclear how these opposing interactions are resolved at the population level.We discover that this conflict between protection and starvation is resolved through emergence of long-range metabolic co-dependence between peripheral and interior cells.As a result, biofilm growth halts periodically, increasing nutrient availability for the sheltered interior cells.

View Article: PubMed Central - PubMed

Affiliation: Division of Biological Sciences, University of California San Diego, California 92093, USA.

ABSTRACT
Cells that reside within a community can cooperate and also compete with each other for resources. It remains unclear how these opposing interactions are resolved at the population level. Here we investigate such an internal conflict within a microbial (Bacillus subtilis) biofilm community: cells in the biofilm periphery not only protect interior cells from external attack but also starve them through nutrient consumption. We discover that this conflict between protection and starvation is resolved through emergence of long-range metabolic co-dependence between peripheral and interior cells. As a result, biofilm growth halts periodically, increasing nutrient availability for the sheltered interior cells. We show that this collective oscillation in biofilm growth benefits the community in the event of a chemical attack. These findings indicate that oscillations support population-level conflict resolution by coordinating competing metabolic demands in space and time, suggesting new strategies to control biofilm growth.

Show MeSH
Related in: MedlinePlus