This paper shows that for microbial communities, ''fences make good neighbors.'' Communities of soil microorganisms perform critical functions: controlling climate, enhancing crop production, and remediation of environmental contamination. Microbial communities in the oral cavity and the gut are of high biomedical interest. Understanding and harnessing the function of these communities is difficult: artificial microbial communities in the laboratory become unstable because of ''winner-takes-all'' competition among species. We constructed a community of three different species of wild-type soil bacteria with syntrophic interactions using a microfluidic device to control spatial structure and chemical communication. We found that defined microscale spatial structure is both necessary and sufficient for the stable coexistence of interacting bacterial species in the synthetic community. A mathematical model describes how spatial structure can balance the competition and positive interactions within the community, even when the rates of production and consumption of nutrients by species are mismatched, by exploiting nonlinearities of these processes. These findings provide experimental and modeling evidence for a class of communities that require microscale spatial structure for stability, and these results predict that controlling spatial structure may enable harnessing the function of natural and synthetic multispecies communities in the laboratory.microbial ͉ microscale ͉ model ͉ stability ͉ microfluidic

This article describes plug-based microfluidic technology that enables rapid detection and drug susceptibility screening of bacteria in samples, including complex biological matrices, without pre-incubation. Unlike conventional bacterial culture and detection methods, which rely on incubation of a sample to increase the concentration of bacteria to detectable levels, this method confines individual bacteria into droplets nanoliters in volume. When single cells are confined into plugs of small volume such that the loading is less than one bacterium per plug, the detection time is proportional to plug volume. Confinement increases cell density and allows released molecules to accumulate around the cell, eliminating the pre-incubation step and reducing the time required to detect the bacteria. We refer to this approach as ‘stochastic confinement’. Using the microfluidic hybrid method, this technology was used to determine the antibiogram — or chart of antibiotic sensitivity — of methicillin-resistant Staphylococcus aureus (MRSA) to many antibiotics in a single experiment and to measure the minimal inhibitory concentration (MIC) of the drug cefoxitin (CFX) against this strain. In addition, this technology was used to distinguish between sensitive and resistant strains of S. aureus in samples of humanblood plasma. High-throughput microfluidic techniques combined with single-cell measurements also enable multiple tests to be performed simultaneously on a single sample containing bacteria. This technology may provide a method of rapid and effective patient-specific treatment of bacterial infections and could be extended to a variety of applications that require multiple functional tests of bacterial samples on reduced timescales.

The development of new thin film fabrication techniques that allow for precise control of degradation and drug release properties could represent an important advance in the fields of drug delivery and biomedicine. Polyelectrolyte layer-by-layer (LBL) thin films can be assembled with nanometer scale control over spatial architecture and morphology, yet very little work has focused on the deconstruction of these ordered thin films for controlled release applications. In this study, hydrolytically degradable LBL thin films are constructed by alternately depositing a degradable poly(beta-amino ester) (polymer 1) and a series of model therapeutic polysaccharides (heparin, low molecular weight heparin, and chondroitin sulfate). These films exhibit pH-dependent, pseudo-first-order degradation and release behavior. The highly versatile and tunable properties of these materials make them exciting candidates for the controlled release of a wide spectrum of therapeutics.

One is a quorum: As few as one to three cells of Pseudomonas aeruginosa bacteria are confined in small volumes by the use of microfluidics. These small numbers of cells are able to activate quorum sensing (QS) pathways and achieve QS‐dependent growth. The results also show that at low numbers of cells, initiation of QS is highly variable within a clonal population.

Blood coagulation often accompanies bacterial infections and sepsis and is generally accepted as a consequence of immune responses. Though many bacterial species can directly activate individual coagulation factors, they have not been shown to directly initiate the coagulation cascade that precedes clot formation. Here we demonstrated, using microfluidics and surface patterning, that the spatial localization of bacteria substantially affects coagulation of human and mouse blood and plasma. Bacillus cereus and Bacillus anthracis, the anthrax-causing pathogen, directly initiated coagulation of blood in minutes when bacterial cells were clustered. Coagulation of human blood by B. anthracis required secreted zinc metalloprotease InhA1, which activated prothrombin and factor X directly (not via factor XII or tissue factor pathways). We refer to this mechanism as 'quorum acting' to distinguish it from quorum sensing-it does not require a change in gene expression, it can be rapid and it can be independent of bacterium-to-bacterium communication.This paper describes a physical and biochemical mechanism responsible for regulating the initiation of human blood coagulation by bacteria. In vivo, coagulation often accompanies bacterial infections of the blood and is believed to be a consequence of immune and inflammatory responses 1-5 . Immune and inflammatory responses cause upregulation of tissue factor on the timescale of hours and lead to increased coagulation 6,7 . One of the few drugs available to treat septic shock, activated protein C, is also an anticoagulant 8 . This coagulation is believed to prevent dissemination of bacteria through the blood 9,10 but also results in serious vascular damage due to blockage and injury of blood vessels 8 . Coagulation accompanying bacterial infections of the blood is particularly relevant for people infected with anthrax, which involves sepsis and disseminated intravascular coagulation caused by the pathogen Bacillus Correspondence should be addressed to R.F.I. (r-ismagilov@uchicago.edu).. AUTHOR CONTRIBUTIONS C.J.K., J.Q.B., M.M., Y.B., R.R.P., T.R.K. and F.S. performed experiments; C.J.K., J.Q.B., M.M., Y.B., R.R.P., T.R.K., F.S., S.H.L., W.-J.T. and R.F.I. designed experiments and analyzed data; C.J.K., W.-J.T. and R.F.I. wrote the paper; A.P.P. and P.S. provided reagents. NIH Public Access Author ManuscriptNat Chem Biol. Author manuscript; available in PMC 2009 June 1. Published in final edited form as:Nat Chem Biol. 2008 December ; 4(12): 742-750. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript anthracis 4 . Here, we considered an alternative and complementary mechanism for the coagulation that accompanies infection: direct activation of the human coagulation cascade through activation of coagulation factors by bacteria.Many bacteria and bacterial components can directly activate individual human coagulation factors. However, direct initiation of the coagulation cascade and the formation of a propagating clot are not typically observed 11-17 ...

In this paper we describe a multijunction microfluidic device for the injection of a substrate into an array of preformed plugs carried by an immiscible fluid in a microchannel. The device uses multiple junctions to inject substrate into preformed plugs without synchronization of the flow of substrate and the array of preformed plugs of reagent, which reduces cross-contamination of the plugs, eliminates formation of small droplets of substrate, and allows a greater range of injection ratios compared to that of a single T-junction. The device was based on a previously developed physical model for transport that was here adapted to describe injection and experimentally verified. After characterization, the device was applied to two biochemical assays, including evaluation of the enzymatic activity of thrombin and determination of the coagulation time of human blood plasma, which both provided reliable results. The reduction of cross-contamination and greater range of injection ratios achieved by this device may improve the processes that involve addition and titration of reagents into plugs, such as high-throughput screening of protein crystallization conditions.In this paper we discuss a physical model of multiphase fluid flow 1,2 during injection of a stream into droplets and the use of this model to design and validate a multijunction microfluidic injector for reliable addition of a substrate into an array of preformed plugs containing reagents. This model has been presented previously for multiphase separation, 1,2 and we used it to describe the related process of injecting reagents into droplets. Microfluidic systems are attractive for miniaturizing laboratory techniques, 3-8 and systems with multiphase flows are useful for compartmentalizing reagents, enhancing mixing, and reducing dispersion but require improved understanding and control. 2,3,6,9-13 In plug-based systems, nanoliter or picoliter droplets are formed within microchannels and carried by an immiscible fluid. 14-16 Each plug contains multiple reagents and can act as a microreactor. 13,17-21 For chemical and biological reactions and analysis, multiple substrates and reagents must be introduced into plugs. Introducing multiple reagents as a plug is forming can be done simply by relying on laminar flow of several streams containing reagents. 13 However, reliable addition of a substrate to preformed plugs is more challenging.Injection into preformed plugs may improve a number of processes such as protein crystallization, 22 synthesis of particles, 23 biological assays, 22 combinatorial chemistry, 24 and chemical synthesis with one or multiple steps. 25,26 In a T-junction, substrate is injected from the side channel into preformed plugs traveling in the main channel ( Figure 1A). Three problems were identified for injection using a T-junction: (i) Cross-contamination between plugs occurred when the substrate stream picked up reagents from a preformed plug and

Eine ist ein Quorum: Nur eine bis drei Zellen von Pseudomonas‐aeruginosa‐Bakterien können mithilfe der Mikrofluidik in kleinen Volumina eingegrenzt werden. Diese wenigen Zellen sind zum Quorum‐Sensing (QS) befähigt und gehen QS‐abhängiges Wachstum ein. Die Befunde ergaben auch, dass bei niedriger Zahl an Zellen das Auslösen von QS innerhalb einer Klonpopulation sehr variabel ist.

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