Mushroom-like Structures Research Articles

The Agost Basin (Betic Cordillera, Alicante province, Spain): a pull-apart basin involving salt tectonics

The Agost Basin is characterized by a Miocene–Quaternary shallow marine and continental infilling controlled by the evolution of several curvilinear faults involving salt tectonics derived from Triassic rocks. From the Serravallian on, the area experienced a horizontal maximum compression with a rotation of the maximum stress axis from E–W to N–S. The resulting deformation gave rise to a strike-slip fault whose evolution is characterized progressively by three stages: (1) stepover/releasing bend with a dextral motion of blocks; (2) very close to pure horizontal compression; and (3) restraining bend with a sinistral movement of blocks. In particular, after an incipient fracturing stage, faults generated a pull-apart basin with terraced sidewall fault and graben subzones developed in the context of a dextral stepover during the lower part of late Miocene p.p. The occurrence of Triassic shales and evaporites played a fundamental role in the tectonic evolution of the study area. The salty material flowed along faults during this stage generating salt walls in root zones and salt push-up structures at the surface. During the purely compressive stage (middle part of late Miocene p.p.) the salt walls were squeezed to form extrusive mushroom-like structures. The large amount of clayish and salty material that surfaced was rapidly eroded and deposited into the basin, generating prograding fan clinoforms. The occurrence of shales and evaporites (both in the margins of the basin and in the proper infilling) favored folding of basin deposits, faulting, and the formation of rising blocks. Later, in the last stage (upper part of late Miocene p.p.), the area was affected by sinistral restraining conditions and faults must have bent to their current shape. The progressive folding of the basin and deformation of margins changed the supply points and finally caused the end of deposition and the beginning of the current erosive systems. On the basis of the interdisciplinary results, the Agost Basin can be considered a key case of the interference between salt tectonics and the evolution of strike-slip fault zones. The reconstructed model has been compared with several scaled sandbox analogical models and with some natural pull-apart basins.

Manufacturing of mushroom-shaped structures and its hydrophobic robustness analysis based on energy minimization approach

The construction of stable hydrophobic surfaces has increasingly gained attention owing to its wide range of potential applications. However, these surfaces may become wet and lose their slip effect owing to insufficient hydrophobic stability. Pillars with a mushroom-shaped tip are believed to enhance hydrophobicity stability. This work presents a facile method of manufacturing mushroom-shaped structures, where, compared with the previously used method, the modulation of the cap thickness, cap diameter, and stem height of the structures is more convenient. The effects of the development time on the cap diameter and overhanging angle are investigated and well-defined mushroom-shaped structures are demonstrated. The effect of the microstructure geometry on the contact state of a droplet is predicted by taking an energy minimization approach and is experimentally validated with nonvolatile ultraviolet-curable polymer with a low surface tension by inspecting the profiles of liquid–vapor interface deformation and tracking the trace of the receding contact line after exposure to ultraviolet light. Theoretical and experimental results show that, compared with regular pillar arrays having a vertical sidewall, the mushroom-like structures can effectively enhance hydrophobic stability. The proposed manufacturing method will be useful for fabricating robust hydrophobic surfaces in a cost-effective and convenient manner.

Axisymmetric jet manipulated using two unsteady minijets

The manipulation of a turbulent axisymmetric jet is experimentally investigated based on two unsteady radial minijets. The Reynolds number is 8000. The mass flow rate ratio$C_{m}$of the two minijets to that of the main jet and the ratio$f_{e}/f_{0}^{\prime }$of the excitation frequency$f_{e}$to the preferred-mode frequency$f_{0}^{\prime }$in the natural jet are examined. The decay rate$K$of the jet centreline mean velocity exhibits a strong dependence on$C_{m}$and$f_{e}/f_{0}^{\prime }$and is classified into three distinct categories in terms of required$C_{m}$, achievable enhancement in$K$and flow physics involved. Great effort is made to understand the flow physics associated with the first category of the manipulated jet, under which$K$can be immensely improved with a very small$C_{m}$. Detailed measurements are conducted upstream and downstream of the nozzle exit using hot-wire, flow visualization and particle imaging velocimetry techniques. Whilst strong entrainment is predominant in the injection plane of the minijets, rapid spread occurs in the orthogonal non-injection plane. Three types of coherent structures are identified, i.e. the contorted ring vortex, two pairs of streamwise vortices and mushroom-like counter-rotating structures sequentially ‘tossed’ out radially in the non-injection plane. Their interactions account for the large rise in$K$. The unsteady disturbance of the minijets is found to play a key role in the formation and interaction of these vortices, which are distinct from those formed under the manipulation of steady minijets and other techniques. A conceptual model of the flow structure under manipulation is proposed.

A CHASE3/GAF sensor hybrid histidine kinase BmsA modulates biofilm formation and motility in Pseudomonas alkylphenolica.

Pseudomonas alkylphenolica is an important strain in the biodegradation of toxic alkylphenols and mass production of bioactive polymannuronate polymers. This strain forms a diverse, 3D biofilm architecture, including mushroom-like aerial structures, circular pellicles and surface spreading, depending on culture conditions. A mutagenesis and complementation study showed that a predicted transmembrane kinase, PSAKL28_21690 (1164 aa), harbouring a periplasmic CHASE3 domain flanked by two transmembrane helices in addition to its cytoplasmic GAF, histidine kinase and three CheY-like response regulator domains, plays a positive role in the formation of the special biofilm architecture and a negative role in swimming activity. In addition, the gene, named here as bmsA, is co-transcribed with three genes encoding proteins with CheR (PSAKL28_21700) and CheB (PSAKL28_21710) domains and response regulator and histidine kinase domains (PSAKL28_21720). This gene cluster is thus named bmsABCD and is found widely distributed in pseudomonads and other bacteria. Deletion of the genes in the cluster, except forbmsA, did not result in changes in biofilm-related phenotypes. The RNA-seq analysis showed that the expression of genes coding for flagellar synthesis was increased when bmsA was mutated. In addition, the expression of rsmZ, which is one of final targets of the Gac regulon, was not significantly altered in the bmsA mutant, and overexpression of bmsA in the gacA mutant did not produce the WT phenotype. These results indicate that the sensory Bms regulon does not affect the upper cascade of the Gac signal transduction pathway for the biofilm-related phenotypes in P. alkylphenolica.

Fabrication Of 3D Nanostructured Multielectrode Arrays By Using Thermal Nanoimprint Lithography To Improve Cell Coupling For Low Signaling Neurons

Event Abstract Back to Event Fabrication Of 3D Nanostructured Multielectrode Arrays By Using Thermal Nanoimprint Lithography To Improve Cell Coupling For Low Signaling Neurons Dominique Decker1*, Sven Ingebrandt1, Holger Rabe1, Karl-Herbert Schäfer1 and Monika Saumer1 1 University of Applied Sciences Kaiserslautern, Department of Informatics and Microsystems Technologie, Germany Motivation Recently a lot of effort was done in optimizing MEA technology in order to enhance signal qualities and to improve the coupling with cells in a culture. Recording performances can be improved by either coating the MEA with artificial or biological polymers or by adding three dimensional nanostructures on top of the sensing pad, thus increasing the surface area and ensuring a tight cell electrode coupling by partly engulfing the nanosized MEA features by the cells [1, 2]. Here we present a fabrication process of nanostructured MEA chips based on nanoimprint lithography (NIL) and electroplating. Compared to other nanostructuring techniques, NIL offers the possibility to fabricate a whole set of nanostructures on several chips at the same time in a fast, simple and inexpensive full wafer process. The nanostructured MEA devices will later be used for action potential measurements and drug testing with neurons with relative weak signals, such as those from the enteric nervous system. Materials and Methods Silicon or glass wafers are vapor-deposited with 20 nm titanium and 200 nm gold layers, followed by a 200 nm thin spin-coated layer of a thermal resist. Nanoimprint lithography is performed (figure 1) with a customized silicon master stamp including a broad range of nanostructures with different geometries, diameters and arrangements. After removing the residual layer with reactive ion etching the nanostructures are filled with gold by electroplating. Microfabrication techniques including photolithography, wet chemical etching and chemical vapor deposition steps are needed to define the leads, the sensing areas and the contact pads of the MEA chips. Subsequently the wafer is cut. The separated chips are bonded to a PCB, encapsulated and prepared for cell culture experiments. Results and Discussion Different nanostructures like meanders, lines, pillars and tubes with diameters from 50 nm up to 800 nm, different heights up to 500 nm and variable distances between the structures have successfully been fabricated on gold-coated substrates. By means of overelectroplating it is also possible to create mushroom-like or muffin-like structures. AFM and SEM pictures show a good structure transfer during NIL and a high uniformity of the electroplated nanostructures over the whole wafer (figure 2). Electrochemical characterization of the fabricated structures is done with cyclic voltammetry and electrochemical impedance spectroscopy. As expected the measurements show an increase of the electrochemical active surface area and a reduction of the impedance compared to planar electrodes. First biocompatibility tests with P19 cells also show a good cell electrode coupling. Conclusion The presented fabrication process incorporates an alternative, high throughput, time saving and thus cost-efficient method for the integration of nanostructures on MEA chips. Different nanostructures are investigated to find an ideal combination of shape, dimension and arrangement for enhancing the signal-to-noise ratio. Future work will be based on recordings with living cells where we intend to work with neurons from the enteric nervous system. These experiments will explore which nanostructures are best suited for cell electrode coupling and thus signal detection from this particular cell type.

Compact Penta-Band Dual ZOR Antenna for Mobile Applications

A compact penta-band dual zeroth order resonator (ZOR) antenna with band-stop filter is proposed for mobile applications. The ZOR antenna is designed with modified mushroom-like structures extended on nonground region to obtain good efficiency and broad bandwidth. This modified mushroom-like structure is confirmed as double negative (DNG) transmission line by full wave simulated dispersion relation. Moreover, a bended patch and a band-stop filter (BSF) are employed to increase efficiency and bandwidth, respectively. The length of each antenna is aboutλ0/10at the resonant frequencies of 900 MHz and 1800 MHz, respectively. The overall dimension of the antenna is 54.4 mm (length) × 4 mm (width) × 5 mm (height). The total efficiencies in low and high bands are measured more than 40% and 70%, respectively.

Marine bacteria from the French Atlantic coast displaying high forming-biofilm abilities anddifferent biofilm 3D architectures.

BackgroundFew studies have reported the species composition of bacterial communities in marine biofilms formed on natural or on man-made existing structures. In particular, the roles and surface specificities of primary colonizers are largely unknown for most surface types. The aim of this study was to obtain potentially pioneering bacterial strains with high forming-biofilm abilities from two kinds of marine biofilms, collected from two different surfaces of the French Atlantic coast: an intertidal mudflat which plays a central role in aquaculture and a carbon steel structure of a harbour, where biofilms may cause important damages.ResultsA collection of 156 marine heterotrophic aerobic bacteria isolated from both biofilms was screened for their ability to form biofilms on polystyrene 96-well microtiter plates. Out of 25 strains able to build a biofilm in these conditions, only four bacteria also formed a thick and stable biofilm on glass surfaces under dynamic conditions. These strains developed biofilms with four different three - dimensional architectures when observed by confocal laser scanning microscopy: Flavobacterium sp. II2003 biofilms harboured mushroom-like structures, Roseobacter sp. IV3009 biofilms were quite homogeneous, Shewanella sp. IV3014 displayed hairy biofilms with horizontal fibres, whereas Roseovarius sp. VA014 developed heterogeneous and tousled biofilms.ConclusionsThis work led for the first time to the obtaining of four marine bacterial strains, potentially pioneering bacteria in marine biofilms, able to adhere to at least two different surfaces (polystyrene and glass) and to build specific 3D biofilms. The four selected strains are appropriate models for a better understanding of the colonization of a surface as well as the interactions that can occur between bacteria in a marine biofilm, which are crucial events for the initiation of biofouling.

Transverse electron-scale instability in relativistic shear flows.

Electron-scale surface waves are shown to be unstable in the transverse plane of a sheared flow in an initially unmagnetized collisionless plasma, not captured by (magneto)hydrodynamics. It is found that these unstable modes have a higher growth rate than the closely related electron-scale Kelvin-Helmholtz instability in relativistic shears. Multidimensional particle-in-cell simulations verify the analytic results and further reveal the emergence of mushroomlike electron density structures in the nonlinear phase of the instability, similar to those observed in the Rayleigh Taylor instability despite the great disparity in scales and different underlying physics. This transverse electron-scale instability may play an important role in relativistic and supersonic sheared flow scenarios, which are stable at the (magneto)hydrodynamic level. Macroscopic (≫c/ωpe) fields are shown to be generated by this microscopic shear instability, which are relevant for particle acceleration, radiation emission, and to seed magnetohydrodynamic processes at long time scales.

Microscopic imaging of the initial stage of diesel spray formation

Detailed measurements of near-nozzle spray formation are essential to better understand and predict the physical processes involved in diesel fuel atomisation. We used long-range microscopy to investigate the primary atomisation of diesel, biodiesel and kerosene fuels in the near-nozzle region, both at atmospheric and realistic engine conditions. High spatial and temporal resolutions allowed a detailed observation of the very emergence of fuel from the nozzle orifice. The fluid that first exited the nozzle resembled mushroom-like structures, as occasionally reported by other researchers for atmospheric conditions, with evidence of interfacial shearing instabilities and stagnation points. We captured the dynamics of this phenomenon using an ultra-fast framing camera with frame rates up to 5 million images per second, and identified these structures as residual fluid trapped in the orifice between injections. The residual fluid has an internal vortex ring motion which results in a slipstream effect that can propel a microscopic ligament of liquid fuel ahead. We showed that this mechanism is not limited to laboratory setups, and that it occurs for diesel fuels injected at engine-like conditions with production injectors. Our findings confirm that fuel can remain trapped in the injector holes after the end of injection. Although we could not measure the hydrocarbon content of the trapped vapourised fluid, we observed that its density was lower than that of the liquid fuel, but higher than that of the in-cylinder gas. We conclude that high-fidelity numerical models should not assume in their initial conditions that the sac and orifices of fuel injectors are filled with in-cylinder gas. Instead, our observations suggest that the nozzle holes should be considered partially filled with a dense fluid.

AAO-assisted synthesis of highly ordered, large-scale TiO2 nanowire arrays via sputtering and atomic layer deposition.

Highly ordered nanoporous anodic aluminum oxide (AAO) thin films were fabricated in oxalic acid under a constant voltage via a two-step anodization process. To investigate the high-aspect-ratio (7.5:1) filling process, both sputtering and atomic layer deposition (ALD) were used to form TiO2 nanowires. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that mushroom-like TiO2 structures were sputtered onto the AAO template surface, and the ALD-coated TiO2 exhibited fine filling results and clear crystal grain boundaries. Large-scale and free-standing TiO2 nanowire arrays were liberated by selectively removing the aluminum substrate and AAO template via a wet etching process with no collapsing or agglomeration after the drying process. ALD-deposited TiO2 nanowire arrays that were 67 nm in diameter and 400 nm high were transferred from the AAO template. The ALD process enabled the rapid, simple synthesis of highly ordered TiO2 nanowire arrays with desired parameters such as diameter, density, and thickness determined using diverse AAO templates.

Fairy chimney erosion rates on Cappadocia ignimbrites, Turkey: Insights from cosmogenic nuclides

Cappadocia, in the Central Anatolian Plateau of Turkey, is famous for its unique landscape and unusual rock formations. The development of this landscape dates back to Late Miocene epoch (c. 10millionyears) when volcanoes spread pyroclastic deposits over an area of about 20,000km2. The volcanism continued for several millions of years and laid down thick and colorful ignimbrite layers. The evolution of the Cappadocian landscape starts with nearly-horizontal plateaus, which are then dissected, usually along cooling fractures, to form mushroom-like structures (hoodoos) locally known as “fairy chimneys”. Different layers of ignimbrites have different resistance to erosion: softer layers (necks) are easier to erode compared to the harder ignimbrites (caps). When the chimneys are isolated, the caps play an important role in slowing further erosion of softer layers. When the caps finally drop or completely erode away, the soft necks of the chimneys are quickly destroyed. Here, for the first time, we have determined the bedrock erosion rates at the three evolution stages of fairy chimneys using the cosmogenic chlorine-36 (36Cl): the pre-chimney (plateaus) stage, the chimney stage and the post-chimney stage. The data show that the plateaus erode at a very low rate between 0.58±0.02cm/ky and 0.93±0.05cm/ky. When dissection of a plateau starts, the erosion rate increases to about 4.5±0.6cm/ky. The caps of chimneys have erosion rates between 3.21±0.36cm/ky and 3.39±0.36cm/ky. Once the chimneys disappear, erosion rates increase significantly to 28.0±9.9cm/ky.

Visualization of pre-set vortices in boundary layer flow over wavy surface in rectangular channel

Smoke-wire flow visualization is used to study the development of pre-set counter-rotating streamwise vortices in boundary layer flow over a wavy surface in a rectangular channel. The formation of the vortices is indicated by the vortical structures on the cross-sectional plane normal to the wavy surface. To obtain uniform spanwise vortex wavelength which will result in uniform vortex size, two types of spanwise disturbances were used: a series of perturbation wires placed prior and normal to the leading edge of the wavy surface, and a jagged pattern in the form of uniform triangles cut at the leading edge. These perturbation wires and jagged pattern induce low-velocity streaks that result in the formation of counter-rotating streamwise vortices that evolve downstream to form the mushroom-like structures on the cross-sectional plane of the flow. The evolution of the most amplified disturbances can be attributed to the formation of these mushroom-like structures. It is also shown that the size of the mushroom-like structures depends on the channel entrance geometry, Reynolds number, and the channel gap.

Complete genome sequence of the mushroom-like aerial structure-forming Pseudomonas alkylphenolia, a platform bacterium for mass production of poly-β-d-mannuronates

Pseudomonas alkylphenolia (KCTC 22206, JCM 16553) metabolizes phenols with an alkyl chain (C1–C5) at the para position. This strain forms mushroom-like aerial structures under p-cresol vapor, and its mutants are exploited to augment the production of poly-β-d-mannuronate and its derivatives. In this study, we report the 5.7Mbp complete genome sequence of P. alkylphenolia, which will provide a basis for biotechnological applications of this strain.

Xanthomonas citri subsp. citri type IV Pilus is required for twitching motility, biofilm development, and adherence.

Bacterial type IV pili (T4P) are long, flexible surface filaments that consist of helical polymers of mostly pilin subunits. Cycles of polymerization, attachment, and depolymerization mediate several pilus-dependent bacterial behaviors, including twitching motility, surface adhesion, pathogenicity, natural transformation, escape from immune system defense mechanisms, and biofilm formation. The Xanthomonas citri subsp. citri strain 306 genome codes for a large set of genes involved in T4P biogenesis and regulation and includes several pilin homologs. We show that X. citri subsp. citri can exhibit twitching motility in a manner similar to that observed in other bacteria such as Pseudomonas aeruginosa and Xylella fastidiosa and that this motility is abolished in Xanthomonas citri subsp. citri knockout strains in the genes coding for the major pilin subunit PilAXAC3241, the ATPases PilBXAC3239 and PilTXAC2924, and the T4P biogenesis regulators PilZXAC1133 and FimXXAC2398. Microscopy analyses were performed to compare patterns of bacterial migration in the wild-type and knockout strains and we observed that the formation of mushroom-like structures in X. citri subsp. citri biofilm requires a functional T4P. Finally, infection of X. citri subsp. citri cells by the bacteriophage (ΦXacm4-11 is T4P dependent. The results of this study improve our understanding of how T4P influence Xanthomonas motility, biofilm formation, and susceptibility to phage infection.

Controlled synthesis, asymmetrical transport behavior and luminescence properties of lanthanide doped ZnO mushroom-like 3D hierarchical structures.

Lanthanide doped ZnO mushroom-like 3D hierarchical structures have been fabricated by polyol-mediated method and characterized by various microstructural and optical techniques. The results indicate that the as-prepared ZnO:Ln(3+) (Ln = Tb, Eu) samples have a hexagonal phase structure and possess a mushroom-like 3D hierarchical morphology. The length of the whole mushroom from stipe bottom to pileus top is about 1.0 μm, and the diameters of pileus and stipe are about 0.8 μm and 0.4 μm, respectively. It is found that the flow of N2 is the key parameter for the formation of the novel ZnO structure and the addition of (NH4)2HPO4 has a prominent effect on the phase structure and the growth of mushroom-like morphology. The potential mechanism of forming this morphology is proposed. The pileus of the formed mushroom is assembled by several radial ZnO:Ln(3+) nanorods, whereas the stipe is composed of over layered ZnO:Ln(3+) nanosheets. Moreover, asymmetrical I-V characteristic curves of ZnO:Ln(3+) mushrooms indicate that the texture composition of the 3D hierarchical morphology might lead to the asymmetrical transport behavior of electrical conductivity. Lanthanide doped ZnO samples can exhibit red or green emission under the excitation of UV light.

Life under flow: A novel microfluidic device for the assessment of anti-biofilm technologies

In the current study, we have developed and fabricated a novel lab-on-a-chip device for the investigation of biofilm responses, such as attachment kinetics and initial biofilm formation, to different hydrodynamic conditions. The microfluidic flow channels are designed using computational fluid dynamic simulations so as to have a pre-defined, homogeneous wall shear stress in the channels, ranging from 0.03 to 4.30 Pa, which are relevant to in-service conditions on a ship hull, as well as other man-made marine platforms. Temporal variations of biofilm formation in the microfluidic device were assessed using time-lapse microscopy, nucleic acid staining, and confocal laser scanning microscopy (CLSM). Differences in attachment kinetics were observed with increasing shear stress, i.e., with increasing shear stress there appeared to be a delay in bacterial attachment, i.e., at 55, 120, 150, and 155 min for 0.03, 0.60, 2.15, and 4.30 Pa, respectively. CLSM confirmed marked variations in colony architecture, i.e.,: (i) lower shear stresses resulted in biofilms with distinctive morphologies mainly characterised by mushroom-like structures, interstitial channels, and internal voids, and (ii) for the higher shear stresses compact clusters with large interspaces between them were formed. The key advantage of the developed microfluidic device is the combination of three architectural features in one device, i.e., an open-system design, channel replication, and multiple fully developed shear stresses.

Flow Stucture of Supersonic Underexpanded Jet With Microjets Injection

Experimental and numerical study of transversal microjets injection influence on the supersonic underexpanded jet flow structure has been performed. Data of measurements and calculation have acceptable agreement. Interaction of microjets with main supersonic jet sets to a decrease of an initial gasdynamic region. Microjets lead to a longitudinal streamwise vortices generation and a mushroom-like flow structures create on an external jet mixing layer. Dissipation of longitudinal streamwise vortices was observed at the second jet cell. Complex gasdynamic flow structure of the supersonic underexpanded jet interacting with supersonic microjets has been studied for the first time. This structure contains system of complex chock waves and expansion waves spreading from the position of the impact microjets/main jet localization place. Future of interaction process a chock-wave structure of main jet with additional shock waves has been studied

Complex architectures formed by alginate drops floating on liquid surfaces

We demonstrate the generation of natural polymeric structures of complex shapes and controlled composition, starting from the collision of aqueous drops of alginate with the surface of a calcium ion-based liquid. We prove that by tuning the impact velocity of the alginate drops on the target surface one can control the floating state of the drops inducing the formation of mushroom-like structures, upon alginate gelation. Besides the geometric peculiarity, the presented approach allows us to provide dual functionality to the polymeric objects, attaching different kinds of functional molecules onto their surface areas, which are immersed or not in the liquid, making such architectures attractive for the development of a novel class of bionanocomposites.

Experimental turbulent mixed convection behind a heated cylinder

Turbulent mixed convection around a horizontal cylinder at constant temperature exposed to a cross-flow is experimentally investigated by means of flow visualizations, 2D particle image velocimetry and thermocouple measurements. This paper analyses the effect of buoyancy when the wake of the cylinder is 3D and fully turbulent. Within this investigation the Reynolds number was chosen to be 1000 and the Richardson number is taken as 2.77 and 0 for comparison with the isothermal case. Results show that buoyancy effects strongly disturb the wake which becomes asymmetric and undergoes an upward deflection. Flow visualizations show the presence of two kinds of structures in the wake with heating of the cylinder. At the rear of the cylinder, the ambient fluid is subject to a high buoyant force due to the great temperature gradients. These significant gradients allow typical mushroom-like structures to emerge in the near wake region but also several diameters downwards the cylinder. In the lower shear-layer, heating is responsible of the generation of Kelvin-Helmholtz instabilities that usually exist at higher Reynolds numbers under isothermal conditions. Moreover comparison of velocity and temperature fields exhibits an opposite behaviour between velocity and temperature fluctuations in the free shear-layers.

Development of the Pseudomonas aeruginosa mushroom morphology and cavity formation by iron-starvation: A mathematical modeling study

We present a mathematical model of mushroom-like architecture and cavity formation in Pseudomonas aeruginosa biofilms. We demonstrate that a proposed disparity in internal friction between the stalk and cap extracellular polymeric substances (EPS) leads to spatial variation in volumetric expansion sufficient to produce the mushroom morphology. The capability of diffusible signals to induce the formation of a fluid-filled cavity within the cap is then investigated. We assume that conversion of bacteria to the planktonic state within the cap occurs in response to the accumulation or depletion of some signal molecule. We (a) show that neither simple nutrient starvation nor signal production by one or more subpopulations of bacteria is sufficient to trigger localized cavity formation. We then (b) demonstrate various hypothetical scenarios that could result in localized cavity formation. Finally, we (c) model iron availability as a detachment signal and show simulation results demonstrating cavity formation by iron starvation. We conclude that iron availability is a plausible mechanism by which fluid-filled cavities form in the cap region of mushroom-like structures.