scholarly journals Morphological Transitions Governed by Density Dependence and Lipoxygenase Activity in Aspergillus flavus

2008 ◽  
Vol 74 (18) ◽  
pp. 5674-5685 ◽  
Author(s):  
S. Horowitz Brown ◽  
R. Zarnowski ◽  
W. C. Sharpee ◽  
N. P. Keller
Keyword(s):  
Linoleic Acid ◽  
Cell Density ◽  
Aspergillus Flavus ◽  
Intermediate Cell ◽  
High Cell ◽  
Dependent Development ◽  
Density Dependent ◽  
Cell Densities ◽  
Overwintering Survival ◽  
Sclerotium Formation

ABSTRACT Aspergillus flavus differentiates to produce asexual dispersing spores (conidia) or overwintering survival structures called sclerotia. Results described here show that these two processes are oppositely regulated by density-dependent mechanisms and that increasing the cell density (from 101 to 107 cells/plate) results in the lowest numbers of sclerotial and the highest numbers of conidial. Extract from spent medium of low-cell-density cultures induced a high-sclerotium-number phenotype, whereas high-cell-density extract increased conidiation. Density-dependent development is also modified by changes in lipid availability. Exogenous linoleic acid increased sclerotial production at intermediate cell densities (104 and 105 cells/plate), whereas oleic and linolenic acids inhibited sclerotium formation. Deletion of Aflox encoding a lipoxygenase (LOX) greatly diminished density-dependent development of both sclerotia and conidia, resulting in an overall increase in the number of sclerotia and a decrease in the number of conidia at high cell densities (>105 cells/plate). Aflox mutants showed decreased linoleic acid LOX activity. Taken together, these results suggest that there is a quorum-sensing mechanism in which a factor(s) produced in dense cultures, perhaps a LOX-derived metabolite, activates conidium formation, while a factor(s) produced in low-density cultures stimulates sclerotium formation.

scholarly journals Chemotactic behaviour ofEscherichia coliat high cell density

2018 ◽  
Author(s):  
Remy Colin ◽  
Knut Drescher ◽  
Victor Sourjik
Keyword(s):  
Cell Density ◽  
Collective Motion ◽  
High Cell Density ◽  
Environmental Gradients ◽  
Model Organism ◽  
High Density ◽  
Intermediate Cell ◽  
High Cell ◽  
Swimming Bacteria ◽  
Cell Densities

AbstractAt high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical interactions of a however still debated nature. Although high-density behaviours are frequent in natural situations, it remained unknown how collective motion affects chemotaxis, the main physiological function of motility, which enables bacteria to follow environmental gradients in their habitats. Here, we systematically investigate this question in the model organismEscherichia coli, varying cell density, cell length, and suspension confinement. The characteristics of the collective motion indicate that hydrodynamic interactions between swimmers made the primary contribution to its emergence. We observe that the chemotactic drift is moderately enhanced at intermediate cell densities, peaks, and is then strongly suppressed at higher densities. Numerical simulations reveal that this suppression occurs because the collective motion disturbs the choreography necessary for chemotactic sensing. We suggest that this physical hindrance imposes a fundamental constraint on high-density behaviours of motile bacteria, including swarming and the formation of multicellular aggregates and biofilms.

scholarly journals Chemotactic behaviour of Escherichia coli at high cell density

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Remy Colin ◽  
Knut Drescher ◽  
Victor Sourjik
Keyword(s):  
Escherichia Coli ◽  
Cell Density ◽  
Collective Motion ◽  
High Cell Density ◽  
Environmental Gradients ◽  
Model Organism ◽  
High Density ◽  
Intermediate Cell ◽  
High Cell ◽  
Cell Densities

AbstractAt high cell density, swimming bacteria exhibit collective motility patterns, self-organized through physical interactions of a however still debated nature. Although high-density behaviours are frequent in natural situations, it remained unknown how collective motion affects chemotaxis, the main physiological function of motility, which enables bacteria to follow environmental gradients in their habitats. Here, we systematically investigate this question in the model organism Escherichia coli, varying cell density, cell length, and suspension confinement. The characteristics of the collective motion indicate that hydrodynamic interactions between swimmers made the primary contribution to its emergence. We observe that the chemotactic drift is moderately enhanced at intermediate cell densities, peaks, and is then strongly suppressed at higher densities. Numerical simulations reveal that this suppression occurs because the collective motion disturbs the choreography necessary for chemotactic sensing. We suggest that this physical hindrance imposes a fundamental constraint on high-density behaviours of motile bacteria, including swarming and the formation of multicellular aggregates and biofilms.

scholarly journals Cell density-dependent stimulation of PAI-1 and hyaluronan synthesis by TGF-β in orbital fibroblasts

2016 ◽  
Vol 229 (2) ◽  
pp. 187-196 ◽  
Author(s):  
Erika Galgoczi ◽  
Florence Jeney ◽  
Annamaria Gazdag ◽  
Annamaria Erdei ◽  
Monika Katko ◽  
...  
Keyword(s):  
Cell Density ◽  
Inverse Correlation ◽  
Fold Increase ◽  
Dermal Fibroblasts ◽  
Negative Regulator ◽  
Dependent Manner ◽  
Density Dependent ◽  
Cell Densities ◽  
Orbital Fibroblasts ◽  
Pai 1

During the course of Graves’ orbitopathy (GO), orbital fibroblasts are exposed to factors that lead to proliferation and extracellular matrix (ECM) overproduction. Increased levels of tissue plasminogen activator inhibitor type 1 (PAI-1 (SERPINE1)) might promote the accumulation of ECM components. PAI-1 expression is regulated by cell density and various cytokines and growth factors including transforming growth factorβ(TGF-β). We examined the effects of increasing cell densities and TGF-β on orbital fibroblasts obtained from GO patients and controls. Responses were evaluated by the measurement of proliferation, PAI-1 expression, and ECM production. There was an inverse correlation between cell density and the per cell production of PAI-1. GO orbital, normal orbital, and dermal fibroblasts behaved similarly in this respect. Proliferation rate also declined with increasing cell densities. Hyaluronan (HA) production was constant throughout the cell densities tested in all cell lines. In both GO and normal orbital fibroblasts, but not in dermal fibroblasts, TGF-β stimulated PAI-1 production in a cell density-dependent manner, reaching up to a five-fold increase above baseline. This has been accompanied by increased HA secretion and pericellular HA levels at high cell densities. Increasing cell density is a negative regulator of proliferation and PAI-1 secretion both in normal and GO orbital fibroblasts; these negative regulatory effects are partially reversed in the presence of TGF-β. Cell density-dependent regulation of PAI-1 expression in the orbit, together with the local cytokine environment, may have a regulatory role in the turnover of the orbital ECM and may contribute to the expansion of orbital soft tissue in GO.

Density-Dependent Growth Adaptation Kinetics in 3T 3 Cell Populations Following Sudden [Ca2+] and Temperature Changes. A Comparison with SV40-3T3 Cells

1979 ◽  
Vol 34 (3-4) ◽  
pp. 279-283 ◽  
Author(s):  
Jürgen van der Bosch ◽  
Ilse Sommer ◽  
Heinz Maier ◽  
Willy Rahmig
Keyword(s):  
Growth Rate ◽  
Cell Density ◽  
Cell Number ◽  
Cell Populations ◽  
3T3 Cells ◽  
Density Dependent ◽  
Cell Densities ◽  
Dependent Growth ◽  
Growth Adaptation ◽  
Stationary Cell

Abstract Lowered extracellular [Ca2+] causes low growth rates and low stationary cell densities in 3T3 cell cultures as compared to physiological [Ca2+]. Under otherwise constant conditions the extra­ cellular [Ca2+] determines a stable stationary cell density, which can be readied by increase of net cell number or decrease of net cell number, depending on cell density at the time of [Ca2+] adjustment. SV40-3T3 cells do not show this [Ca2+] dependency. At 39 °C 3T3 and SV40-3T3 cell populations show an increased growth rate at low cell densities as compared to cell populations at 35 °C. Approaching the stationary density the growth rate of both cell sorts is reduced faster at 39 °C than at 35 °C, leading to lower stationary cell densities at 39 °C than at 35 °C. A temperature change from 39 °C to 35 °C or in the opposite direction can affect the stationary cell density of 3T3 cell populations only if applied before reduction of growth rate by density-dependent growth-inhibiting principles has taken place.

The intra-genus and inter-species quorum-sensing autoinducers exert distinct control over Vibrio cholerae biofilm formation and dispersal

2019 ◽  
Author(s):  
Andrew A. Bridges ◽  
Bonnie L. Bassler
Keyword(s):  
Quorum Sensing ◽  
Vibrio Cholerae ◽  
Cell Density ◽  
Biofilm Formation ◽  
Specific Information ◽  
High Cell ◽  
Coincidence Detector ◽  
Sensing System ◽  
Quorum Sensing System ◽  
Cell Densities

AbstractVibrio cholerae possesses multiple quorum-sensing systems that control virulence and biofilm formation among other traits. At low cell densities, when quorum-sensing autoinducers are absent, V. cholerae forms biofilms. At high cell densities, when autoinducers have accumulated, biofilm formation is repressed and dispersal occurs. Here, we focus on the roles of two well-characterized quorum-sensing autoinducers that function in parallel. One autoinducer, called CAI-1, is used to measure vibrio abundance, and the other autoinducer, called AI-2, is a broadly-made universal autoinducer that is presumed to enable V. cholerae to assess the total bacterial cell density of the vicinal community. The two V. cholerae autoinducers funnel information into a shared signal relay pathway. This feature of the quorum-sensing system architecture has made it difficult to understand how specific information can be extracted from each autoinducer, how the autoinducers might drive distinct output behaviors, and in turn, how the bacteria use quorum sensing to distinguish self from other in bacterial communities. We develop a live-cell biofilm formation and dispersal assay that allows examination of the individual and combined roles of the two autoinducers in controlling V. cholerae behavior. We show that the quorum-sensing system works as a coincidence detector in which both autoinducers must be present simultaneously for repression of biofilm formation to occur. Within that context, the CAI-1 quorum-sensing pathway is activated when only a few V. cholerae cells are present, whereas the AI-2 pathway is activated only at much higher cell density. The consequence of this asymmetry is that exogenous sources of AI-2, but not CAI-1, contribute to satisfying the coincidence detector to repress biofilm formation and promote dispersal. We propose that V. cholerae uses CAI-1 to verify that some of its kin are present before committing to the high-cell-density quorum-sensing mode, but it is, in fact, the universal autoinducer AI-2, that sets the pace of the V. cholerae quorum-sensing program. This first report of unique roles for the different V. cholerae autoinducers suggests that detection of self fosters a distinct outcome from detection of other.

scholarly journals Sociality in Escherichia coli: Enterochelin Is a Private Good at Low Cell Density and Can Be Shared at High Cell Density

2015 ◽  
Vol 197 (13) ◽  
pp. 2122-2128 ◽  
Author(s):  
Rebecca L. Scholz ◽  
E. Peter Greenberg
Keyword(s):  
Escherichia Coli ◽  
Cell Density ◽  
Iron Acquisition ◽  
Partial Privatization ◽  
High Cell ◽  
Wild Type ◽  
Content Type ◽  
Cell Densities ◽  
The Cost ◽  
Low Cell Density

ABSTRACTMany bacteria produce secreted iron chelators called siderophores, which can be shared among cells with specific siderophore uptake systems regardless of whether the cell produces siderophores. Sharing secreted products allows freeloading, where individuals use resources without bearing the cost of production. Here we show that theEscherichia colisiderophore enterochelin is not evenly shared between producers and nonproducers. Wild-typeEscherichia coligrows well in low-iron minimal medium, and an isogenic enterochelin synthesis mutant (ΔentF) grows very poorly. The enterochelin mutant grows well in low-iron medium supplemented with enterochelin. At high cell densities the ΔentFmutant can compete equally with the wild type in low-iron medium. At low cell densities the ΔentFmutant cannot compete. Furthermore, the growth rate of the wild type is unaffected by cell density. The wild type grows well in low-iron medium even at very low starting densities. Our experiments support a model where at least some enterochelin remains associated with the cells that produce it, and the cell-associated enterochelin enables iron acquisition even at very low cell density. Enterochelin that is not retained by producing cells at low density is lost to dilution. At high cell densities, cell-free enterochelin can accumulate and be shared by all cells in the group. Partial privatization is a solution to the problem of iron acquisition in low-iron, low-cell-density habitats. Cell-free enterochelin allows for iron scavenging at a distance at higher population densities. Our findings shed light on the conditions under which freeloaders might benefit from enterochelin uptake systems.IMPORTANCESociality in microbes has become a topic of great interest. One facet of sociality is the sharing of secreted products, such as the iron-scavenging siderophores. We present evidence that theEscherichia colisiderophore enterochelin is relatively inexpensive to produce and is partially privatized such that it can be efficiently shared only at high producer cell densities. At low cell densities, cell-free enterochelin is scarce and only enterochelin producers are able to grow in low-iron medium. Because freely shared products can be exploited by freeloaders, this partial privatization may help explain how enterochelin production is stabilized inE. coliand may provide insight into when enterochelin is available for freeloaders.

scholarly journals Cell Density Affects the Detection of Chk1 Target Engagement by the Selective Inhibitor V158411

2017 ◽  
Vol 23 (2) ◽  
pp. 144-153
Author(s):  
Clara C. Geneste ◽  
Andrew J. Massey
Keyword(s):  
Cell Density ◽  
Drug Target ◽  
High Cell ◽  
Target Engagement ◽  
Molecule Inhibitor ◽  
Chk1 Inhibitor ◽  
Cell Densities ◽  
Cellular Thermal Shift Assay ◽  
The Relationship ◽  
Assay Conditions

Understanding drug target engagement and the relationship to downstream pharmacology is critical for drug discovery. Here we have evaluated target engagement of Chk1 by the small-molecule inhibitor V158411 using two different target engagement methods (autophosphorylation and cellular thermal shift assay [CETSA]). Target engagement measured by these methods was subsequently related to Chk1 inhibitor–dependent pharmacology. Inhibition of autophosphorylation was a robust method for measuring V158411 Chk1 target engagement. In comparison, while target engagement determined using CETSA appeared robust, the V158411 CETSA target engagement EC50 values were 43- and 19-fold greater than the autophosphorylation IC50 values. This difference was attributed to the higher cell density in the CETSA assay configuration. pChk1 (S296) IC50 values determined using the CETSA assay conditions were 54- and 33-fold greater than those determined under standard conditions and were equivalent to the CETSA EC50 values. Cellular conditions, especially cell density, influenced the target engagement of V158411 for Chk1. The effects of high cell density on apparent compound target engagement potency should be evaluated when using target engagement assays that necessitate high cell densities (such as the CETSA conditions used in this study). In such cases, the subsequent relation of these data to downstream pharmacological changes should therefore be interpreted with care.

scholarly journals 3D bioprinting of high cell-density heterogeneous tissue models through spheroid fusion within self-healing hydrogels

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Andrew C. Daly ◽  
Matthew D. Davidson ◽  
Jason A. Burdick
Keyword(s):  
Cell Density ◽  
Spatial Organization ◽  
High Cell Density ◽  
Self Healing ◽  
High Cell ◽  
Cellular Models ◽  
Functional Features ◽  
Cell Densities ◽  
Tissue Models

AbstractCellular models are needed to study human development and disease in vitro, and to screen drugs for toxicity and efficacy. Current approaches are limited in the engineering of functional tissue models with requisite cell densities and heterogeneity to appropriately model cell and tissue behaviors. Here, we develop a bioprinting approach to transfer spheroids into self-healing support hydrogels at high resolution, which enables their patterning and fusion into high-cell density microtissues of prescribed spatial organization. As an example application, we bioprint induced pluripotent stem cell-derived cardiac microtissue models with spatially controlled cardiomyocyte and fibroblast cell ratios to replicate the structural and functional features of scarred cardiac tissue that arise following myocardial infarction, including reduced contractility and irregular electrical activity. The bioprinted in vitro model is combined with functional readouts to probe how various pro-regenerative microRNA treatment regimes influence tissue regeneration and recovery of function as a result of cardiomyocyte proliferation. This method is useful for a range of biomedical applications, including the development of precision models to mimic diseases and the screening of drugs, particularly where high cell densities and heterogeneity are important.

scholarly journals Cell density-dependent linoleic acid toxicity to Saccharomyces cerevisiae

2011 ◽  
Vol 11 (5) ◽  
pp. 408-417 ◽  
Author(s):  
Túlio César Ferreira ◽  
Lídia Maria Pepe de Moraes ◽  
Élida Geralda Campos
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Linoleic Acid ◽  
Cell Density ◽  
Density Dependent ◽  
Acid Toxicity

scholarly journals 3D bioprinting of high cell-density heterogeneous tissue models through spheroid fusion within self-healing hydrogels

2020 ◽  
Author(s):  
Andrew C. Daly ◽  
Matthew D. Davidson ◽  
Jason A. Burdick
Keyword(s):  
Cell Density ◽  
Spatial Organization ◽  
High Cell Density ◽  
Self Healing ◽  
High Cell ◽  
Cellular Models ◽  
Functional Features ◽  
Cell Densities ◽  
Tissue Models

AbstractCellular models are needed to study human development and disease in vitro, including the screening of drugs for toxicity and efficacy. However, current approaches are limited in the engineering of functional tissue models with requisite cell densities and heterogeneity to appropriately model cell and tissue behaviors. Here, we develop a new bioprinting approach to transfer spheroids into self-healing support hydrogels at high resolution, which enables their patterning and fusion into high-cell density microtissues of prescribed spatial organization. As an example application, we bioprint induced pluripotent stem cell-derived cardiac microtissue models with spatially controlled cardiomyocyte and fibroblast cell ratios to replicate the structural and functional features of scarred cardiac tissue that arise following myocardial infarction, including reduced contractility and irregular electrical activity. The bioprinted in vitro model is combined with functional readouts to probe how various pro-regenerative microRNA treatment regimes influence tissue regeneration and recovery of function as a result of cardiomyocyte proliferation. This method is useful for a range of biomedical applications, including the development of precision models to mimic diseases and for the screening of drugs, particularly where high cell densities and heterogeneity are important.

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