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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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Roles of carbon and nitrogen in biofilm growth oscillations. a, Effect of increasing carbon (glycerol) or nitrogen (glutamate) availability on the oscillations. While increasing glutamate by 5 times of the normal MSgg levels leads to quenching of the oscillation, increasing glycerol by 5 times does not. b, Colony growth of mutant strain with rocG deletion. B. subtilis NCIB 3610 has two glutamate dehydrogenases (GDH), rocG and gudB. While gudB is constitutively expressed, rocG expression is subject to carbon catabolite repression18. The oscillatory growth of the rocG deletion strain indicates that carbon-source dependent regulation of rocG expression is not required for biofilm oscillations.
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Figure 6: Roles of carbon and nitrogen in biofilm growth oscillations. a, Effect of increasing carbon (glycerol) or nitrogen (glutamate) availability on the oscillations. While increasing glutamate by 5 times of the normal MSgg levels leads to quenching of the oscillation, increasing glycerol by 5 times does not. b, Colony growth of mutant strain with rocG deletion. B. subtilis NCIB 3610 has two glutamate dehydrogenases (GDH), rocG and gudB. While gudB is constitutively expressed, rocG expression is subject to carbon catabolite repression18. The oscillatory growth of the rocG deletion strain indicates that carbon-source dependent regulation of rocG expression is not required for biofilm oscillations.

Mentions: Given that biofilms typically form under nutrient limited conditions and bacterial growth is generally controlled by metabolism, we hypothesized that metabolic limitation plays a key role in the observed periodic halting of biofilm expansion. In particular, after determining that carbon source limitation did not play an essential role in the oscillations (Extended Data Fig. 2), we focused on nitrogen limitation. The standard biofilm growth media (MSgg, see Methods: Growth conditions) used to study B. subtilis biofilm development contains glutamate as the only nitrogen source16. In most organisms including B. subtilis, glutamate is combined with ammonium by glutamine synthetase (GS) to produce glutamine, which is essential for biomass production and growth (Fig. 2a)17. Cells can obtain the necessary ammonium from glutamate through the enzymatic activity of glutamate dehydrogenase (GDH), expressed by the rocG or gudB genes in the undomesticated B. subtilis used in this study (Fig. 2a)18–20. To determine whether biofilms experience glutamine limitation, we measured expression of nasA, one of several genes activated in response to a lack of glutamine21. Results show that biofilms indeed experience glutamine limitation during growth. Specifically, supplementation of growth media directly with glutamine reduced nasA promoter expression, but did not affect expression of a constitutive promoter, confirming glutamine limitation within the biofilm (Fig. 2b). More strikingly, addition of exogenous glutamine eliminated periodic halting of biofilm growth (Fig. 2c and Extended Data Fig. 3a). These findings suggest that glutamine limitation plays a critical role in the observed oscillations during biofilm expansion.


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)

Roles of carbon and nitrogen in biofilm growth oscillations. a, Effect of increasing carbon (glycerol) or nitrogen (glutamate) availability on the oscillations. While increasing glutamate by 5 times of the normal MSgg levels leads to quenching of the oscillation, increasing glycerol by 5 times does not. b, Colony growth of mutant strain with rocG deletion. B. subtilis NCIB 3610 has two glutamate dehydrogenases (GDH), rocG and gudB. While gudB is constitutively expressed, rocG expression is subject to carbon catabolite repression18. The oscillatory growth of the rocG deletion strain indicates that carbon-source dependent regulation of rocG expression is not required for biofilm oscillations.
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Related In: Results  -  Collection

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Figure 6: Roles of carbon and nitrogen in biofilm growth oscillations. a, Effect of increasing carbon (glycerol) or nitrogen (glutamate) availability on the oscillations. While increasing glutamate by 5 times of the normal MSgg levels leads to quenching of the oscillation, increasing glycerol by 5 times does not. b, Colony growth of mutant strain with rocG deletion. B. subtilis NCIB 3610 has two glutamate dehydrogenases (GDH), rocG and gudB. While gudB is constitutively expressed, rocG expression is subject to carbon catabolite repression18. The oscillatory growth of the rocG deletion strain indicates that carbon-source dependent regulation of rocG expression is not required for biofilm oscillations.
Mentions: Given that biofilms typically form under nutrient limited conditions and bacterial growth is generally controlled by metabolism, we hypothesized that metabolic limitation plays a key role in the observed periodic halting of biofilm expansion. In particular, after determining that carbon source limitation did not play an essential role in the oscillations (Extended Data Fig. 2), we focused on nitrogen limitation. The standard biofilm growth media (MSgg, see Methods: Growth conditions) used to study B. subtilis biofilm development contains glutamate as the only nitrogen source16. In most organisms including B. subtilis, glutamate is combined with ammonium by glutamine synthetase (GS) to produce glutamine, which is essential for biomass production and growth (Fig. 2a)17. Cells can obtain the necessary ammonium from glutamate through the enzymatic activity of glutamate dehydrogenase (GDH), expressed by the rocG or gudB genes in the undomesticated B. subtilis used in this study (Fig. 2a)18–20. To determine whether biofilms experience glutamine limitation, we measured expression of nasA, one of several genes activated in response to a lack of glutamine21. Results show that biofilms indeed experience glutamine limitation during growth. Specifically, supplementation of growth media directly with glutamine reduced nasA promoter expression, but did not affect expression of a constitutive promoter, confirming glutamine limitation within the biofilm (Fig. 2b). More strikingly, addition of exogenous glutamine eliminated periodic halting of biofilm growth (Fig. 2c and Extended Data Fig. 3a). These findings suggest that glutamine limitation plays a critical role in the observed oscillations during biofilm expansion.

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