Oxygen Profiles in, and in the Agar Beneath, Colonies of Bacillus Cereus, Staphylococcus Albus and Escherichia Coli

Peters, Adrian; Wimpenny, J. W. T.; Coombs, Jana

doi:10.1099/00221287-133-5-1257

Cited by 40 publications

(42 citation statements)

References 7 publications

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“…This aspect and its mucoid appearance suggest a model where the MV uses secretions to reduce cell density and expand outwards and upwards. Moving to the surface will allow cells to gain the best access to oxygen, which is strongly growth-limiting within colonies (13)(14)(15)(16)21). We used confocal imaging to assess the spatial patterning of the MV within WT colonies.…”

Section: Resultsmentioning

confidence: 99%

“…This high cell density readily generates localized nutrient limitation and, particularly, the existence of microgradients, whereby the availability of nutrients decreases the further one goes into the cell mass and away from the nutrient source (12). There is good evidence that these gradients commonly occur in a range of systems, both when nutrients come from the surface to which cells attach, and when nutrients diffuse in from the environment (13)(14)(15)(16)(17). Moreover, there is good reason to believe that these microgradients will be central to understanding microbial phenotypes.…”

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confidence: 99%

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Importance of positioning for microbial evolution

Kim

Racimo

Schluter

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

144

207

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Microbes commonly live in dense surface-attached communities where cells layer on top of one another such that only those at the edges have unimpeded access to limiting nutrients and space. Theory predicts that this simple spatial effect, akin to plants competing for light in a forest, generates strong natural selection on microbial phenotypes. However, we require direct empirical tests of the importance of this spatial structuring. Here we show that spontaneous mutants repeatedly arise, push their way to the surface, and dominate colonies of the bacterium Pseudomonas fluorescens Pf0-1. Microscopy and modeling suggests that these mutants use secretions to expand and push themselves up to the growth surface to gain the best access to oxygen. Physically mixing the cells in the colony, or introducing space limitations, largely removes the mutant's advantage, showing a key link between fitness and the ability of the cells to position themselves in the colony. We next follow over 500 independent adaptation events and show that all occur through mutation of a single repressor of secretions, RsmE, but that the mutants differ in competitiveness. This process allows us to map the genetic basis of their adaptation at high molecular resolution and we show how evolutionary competitiveness is explained by the specific effects of each mutation. By combining population level and molecular analyses, we demonstrate how living in dense microbial communities can generate strong natural selection to reach the growing edge.bacteria | biofilm | experimental evolution | social interaction

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Importance of positioning for microbial evolution

Kim

Racimo

Schluter

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

144

207

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“…A tryptophan residue in the PASd domain that corresponds to residue 745 in the full-length protein was changed to an alanine by site-directed mutagenesis (GenScript). Expression of RmcA PAS -His 6 and RmcA PAS-W745A -His 6 was carried out in E. coli BL21 (DE3) pMgK, which contains a plasmid encoding the genes for three rare tRNAs (Northeast Structural Genomics Research Network). Cultures were grown at 37°C with shaking at 250 rpm to OD 600 = 0.5 in Terrific Broth medium with 35 μg/mL kanamycin and 100 μg/mL ampicillin.…”

Section: Methodsmentioning

confidence: 99%

“…These conditions arise in the presence of poised-potential electrodes or insoluble minerals, such as iron oxides (3)(4)(5), and in multicellular communities (biofilms) where the formation of chemical gradients leads to oxidant limitation for cells at depth (6)(7)(8)(9). Diverse microbes secrete redoxactive compounds with the capacity to function as electron shuttles (10)(11)(12).…”

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confidence: 99%

Electron-shuttling antibiotics structure bacterial communities by modulating cellular levels of c-di-GMP

Okegbe

Fields

Cole

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

101

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Diverse organisms secrete redox-active antibiotics, which can be used as extracellular electron shuttles by resistant microbes. Shuttlemediated metabolism can support survival when substrates are available not locally but rather at a distance. Such conditions arise in multicellular communities, where the formation of chemical gradients leads to resource limitation for cells at depth. In the pathogenic bacterium Pseudomonas aeruginosa PA14, antibiotics called phenazines act as oxidants to balance the intracellular redox state of cells in anoxic biofilm subzones. PA14 colony biofilms show a profound morphogenic response to phenazines resulting from electron acceptor-dependent inhibition of ECM production. This effect is reminiscent of the developmental responses of some eukaryotic systems to redox control, but for bacterial systems its mechanistic basis has not been well defined. Here, we identify the regulatory protein RmcA and show that it links redox conditions to PA14 colony morphogenesis by modulating levels of bis-(3′,5′)-cyclic-dimeric-guanosine (c-di-GMP), a second messenger that stimulates matrix production, in response to phenazine availability. RmcA contains four Per-Arnt-Sim (PAS) domains and domains with the potential to catalyze the synthesis and degradation of c-di-GMP. Our results suggest that phenazine production modulates RmcA activity such that the protein degrades c-di-GMP and thereby inhibits matrix production during oxidizing conditions. RmcA thus forms a mechanistic link between cellular redox sensing and community morphogenesis analogous to the functions performed by PAS-domain-containing regulatory proteins found in complex eukaryotes.W hen microbial cells cannot import or are physically separated from metabolic electron donors or acceptors, diffusible compounds can act as electron carriers and support survival on these substrates (1, 2). These conditions arise in the presence of poised-potential electrodes or insoluble minerals, such as iron oxides (3-5), and in multicellular communities (biofilms) where the formation of chemical gradients leads to oxidant limitation for cells at depth (6-9). Diverse microbes secrete redoxactive compounds with the capacity to function as electron shuttles (10-12). In the pathogenic bacterium Pseudomonas aeruginosa PA14, electron-shuttling antibiotics called phenazines support survival on poised-potential electrodes and balance the intracellular redox state of cells in anoxic biofilm subzones (1, 9).Similar to those formed by many species of microbes, colonies of PA14 develop intricate wrinkle structures on agar-solidified growth media (13). Phenazines profoundly alter PA14 colony morphogenesis, inhibiting the onset of wrinkle formation and changing the organization of wrinkles (12) (Fig. 1A). Modeling of resource availability within colonies suggests that the earlier increase in the colony surface area-to-volume ratio in phenazine-null (Δphz) mutants maximizes access to oxygen for cells that would otherwise become limited for oxidant (14). Measurements of...

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“…An unsolved problem is, however, why different respiratory processes are affected to different extent: for example, aerobic growth of strain 2960 is unaffected, H2 oxidation is partly defective, and nitrate respiration and in vivo cytochrome oxidase (Nadi test) are completely defective. The ability to grow aerobically in liquid medium and the Nadi-negative phenotype are not necessarily two conflicting observations, because the Nadi test uses colonies in which the cells are known to be in microaerobic rather than aerobic state (Peters et al, 1987). As far as mutants LO505 and 2606::Tn5-20 are concerned, they both have residual protoporphyrinogen IX oxidase activity; i.e.…”

Section: Discussionmentioning

confidence: 99%