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Examples of radial colony patterns that have been previously described for various microbes are highlighted. Different mechanisms can underlie the patterning, including (A) redox metabolism in P. aeruginosa (7); (B) expansion of the biomass of two metabolically interacting Pseudomonas stutzeri strains in response to cycling oxic/anoxic conditions (15); (C) dye-binding in P. putida (9); (D) sporulation and the nitrogen stress response in B. subtilis microcolonies (6); (E) developmental switch between motility and biofilm formation in Listeria monocytogenes (16); and (F and G) swarming behavior of Proteus mirabilis (17) and K. aerogenes (10). In P. putida and K. aerogenes, the cyclic changes described have been linked to the presence of a circadian clock. The figure was created on BioRender.com.
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Bacteria display a remarkable capacity to organize themselves in space and time within biofilms. Traditionally, the spatial organization of biofilms has been dissected vertically; however, biofilms can exhibit complex, temporally structured, two-dimensional radial patterns while spreading on a surface. Kahl and colleagues report a ring pattern that...
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... cell types of Bacillus subtilis (3) and curli-producing and flagellated cells of Escherichia coli (4). In addition to biofilm stratification, bacterial populations may display diverse radial patterns when expanding on an agar-solidified surface, e.g., during various motility types (5) or during complex colony formation (see examples in Fig. 1). Intriguingly, the spatial patterns of these expanding colonies display remarkable periodic cycles when observed from above. Such spatial self-organization could either occur in a fluctuating environment or develop under constant conditions (e.g., alternating sporulation and nitrogen stress response in Bacillus subtilis colony sections ...
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... was first tested in a nonphotosynthetic bacterium, Pseudomonas putida, about 10 years ago (9). Cultures were grown under 24 h light-dark (LD) cycles on plates with dyes binding to proteins or extracellular polymeric substances. The growth pattern was synchronized with the LD cycles and persisted when the plates were subsequently kept in darkness (Fig. 1). This was surprising at the time, as nonphotosynthetic bacteria were generally considered to lack circadian machinery. Whether P. aeruginosa exhibits self-sustained oscillations in constant darkness following growth under LD cycles has not been tested, as an investigation of the circadian clock was not within the scope of the study by ...
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... protocols, rhythms in constant conditions are typically examined by following the synchronization of samples with environmental cycles or by the addition of a synchronizing agent. For instance, as discussed above, the presence of a free-running rhythm is observed in the ring formation of P. putida following growth under LD cycles ( [9] and Fig. 1). When cultures were placed under constant light or darkness from the beginning of the experiment, the ability to form rings was lost in most cultures. Among synchronizing agents, melatonin has been shown to contribute to the synchronization of circadian rhythms in animals. Interestingly, the addition of melatonin is required for the ...
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... to form rings was lost in most cultures. Among synchronizing agents, melatonin has been shown to contribute to the synchronization of circadian rhythms in animals. Interestingly, the addition of melatonin is required for the circadian swarming behavior of Klebsiella aerogenes, and it also synchronizes circadian reporter gene expression (10) (Fig. 1), suggesting that melatonin may also act as a synchronizer for the circadian rhythms of enteric ...
