Abstract:Bioluminescence imaging experiments were carried out to characterize spatio-temporal patterns of bacterial self-organization in active suspensions (cultures) of bioluminescent Escherichia coli and its mutants. An analysis of the effects of mutations shows that spatio-temporal patterns formed in standard microtitre plates are not related to the chemotaxis system of bacteria. In fact, these patterns are strongly dependent on the properties of mutants that characterize them as self-phoretic (non-flagellar) swimme… Show more
“…E. coli can produce millimolar concentrations of indole from tryptophan by means of tryptophanase (TnaA) during the stationary growth phase under nutrient-rich conditions 16 . The ability of indole to be excreted into the extracellular medium is strong and indole has good volatility, thus the growth rate of E. coli can be selectively enhanced by gentle agitation to increase the signal response of indole for targeted analysis, regulated by numerous pathways that typically connect growth to nutrient availability (free tryptophan) 21 . Thus, the enhancement of indole emission during the early culture time of bacteria is particularly beneficial for the rapid identification of E. coli .Figure 4Time profiles of indole signal ( m/z 116) detected by CDI-MS from the headspace of simulated blood cultures with different initial concentrations of E. coli (negative ionization mode).…”
Escherichia coli is an important pathogen of nosocomial infection in clinical research, Thus, exploring new methods for the rapid detection of this pathogen is urgent. We reported the early release of molecular volatile indole vapour of E. coli cultures and blood cultures analyzed by direct atmospheric corona discharge ionization mass spectrometry (CDI-MS). The concentration of indole in E. coli cultures remarkably increases during the early log and lag phases of bacterial growth, thereby enabling early detection. Technical replicates were cultivated for 3 days for reference diagnosis using current conventional bacteraemia detection. A reference MS screen of common microbes from other genera confirmed that the peaks at m/z 116 signal corresponded to indole were specifically present in E. coli. Our results indicated that volatile indole based on CDI-MS without the need for any sample pretreatment is highly suitable for the reliable and cost-efficient differentiation of E. coli, especially for bacteraemia in humans.
“…E. coli can produce millimolar concentrations of indole from tryptophan by means of tryptophanase (TnaA) during the stationary growth phase under nutrient-rich conditions 16 . The ability of indole to be excreted into the extracellular medium is strong and indole has good volatility, thus the growth rate of E. coli can be selectively enhanced by gentle agitation to increase the signal response of indole for targeted analysis, regulated by numerous pathways that typically connect growth to nutrient availability (free tryptophan) 21 . Thus, the enhancement of indole emission during the early culture time of bacteria is particularly beneficial for the rapid identification of E. coli .Figure 4Time profiles of indole signal ( m/z 116) detected by CDI-MS from the headspace of simulated blood cultures with different initial concentrations of E. coli (negative ionization mode).…”
Escherichia coli is an important pathogen of nosocomial infection in clinical research, Thus, exploring new methods for the rapid detection of this pathogen is urgent. We reported the early release of molecular volatile indole vapour of E. coli cultures and blood cultures analyzed by direct atmospheric corona discharge ionization mass spectrometry (CDI-MS). The concentration of indole in E. coli cultures remarkably increases during the early log and lag phases of bacterial growth, thereby enabling early detection. Technical replicates were cultivated for 3 days for reference diagnosis using current conventional bacteraemia detection. A reference MS screen of common microbes from other genera confirmed that the peaks at m/z 116 signal corresponded to indole were specifically present in E. coli. Our results indicated that volatile indole based on CDI-MS without the need for any sample pretreatment is highly suitable for the reliable and cost-efficient differentiation of E. coli, especially for bacteraemia in humans.
“…Let us finally mention that, to explain pattern formation in experiments with E. coli bacteria in which chemotaxis plays no role [164], the authors of reference [164] have suggested that phoretic interactions might also play a role for bacteria. Clearly, this far-reaching suggestion calls for further explorations.…”
The past two decades have seen a remarkable progress in the development of synthetic colloidal agents which are capable of creating directed motion in an unbiased environment at the microscale. These self-propelling particles are often praised for their enormous potential to self-organize into dynamic nonequilibrium structures such as living clusters, synchronized superrotor structures or self-propelling molecules featuring a complexity which is rarely found outside of the living world. However, the precise mechanisms underlying the formation and dynamics of many of these structures are still barely understood, which is likely to hinge on the gaps in our understanding of how active colloids interact. In particular, besides showing comparatively short-ranged interactions which are well known from passive colloids (Van der Waals, electrostatic etc.), active colloids show novel hydrodynamic interactions as well as phoretic and substrate-mediated “osmotic” cross-interactions which hinge on the action of the phoretic field gradients which are induced by the colloids on other colloids in the system. The present article discusses the complexity and the intriguing properties of these interactions which in general are long-ranged, non-instantaneous, nonpairwise and non-reciprocal and which may serve as key ingredients for the design of future nonequilibrium colloidal materials. Besides providing a brief overview on the state of the art of our understanding of these interactions a key aim of this review is to emphasize open key questions and corresponding open challenges.
“…Let us finally mention that, to explain pattern formation in experiments with E.coli bacteria in which chemotaxis plays no role [163], the authors of ref. [163] have suggested that phoretic interactions might also play a role for bacteria. Clearly, this far-reaching suggestion calls for further explorations.…”
Despite a mounting evidence that the same gradients which active colloids use for swimming, induce important crossinteractions (phoretic interaction), they are still ignored in most many-body descriptions, perhaps to avoid complexity and a zoo of unknown parameters. Here we derive a simple model, which reduces phoretic far-field interactions to a pair-interaction whose strength is mainly controlled by one genuine parameter (swimming speed). The model suggests that phoretic interactions are generically important for autophoretic colloids (unless effective screening of the phoretic fields is strong) and should dominate over hydrodynamic interactions for the typical case of half-coating and moderately nonuniform surface mobilities. Unlike standard minimal models, but in accordance with canonical experiments, our model generically predicts dynamic clustering in active colloids at low density. This suggests that dynamic clustering can emerge from the interplay of screened phoretic attractions and active diffusion.
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