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Team:BCCS-Bristol/Modeling-Parameters
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=== Run Tumble motion === | === Run Tumble motion === | ||
Revision as of 21:33, 11 August 2008
Modelling Parameters
Bacteria
| Attribute | Value | Strain | Justification | Reference |
| Length | 2μm | MG1655 | Values come from the University of Alberta’s datasheet on MG1655, produced to aid modelling. There is variability in size between strains - for instance, AW405 length varies between 1.5±0.2μm. But University of Alberta datasheet is specifically for MG1655. | [http://redpoll.pharmacy.ualberta.ca/CCDB/cgi-bin/STAT_NEW.cgi University of Alberta] |
| Diameter | 0.8μm | MG1655 | [http://redpoll.pharmacy.ualberta.ca/CCDB/cgi-bin/STAT_NEW.cgi University of Alberta] | |
| Shape | Circle r =0.714μm | MG1655 | Actually rod-like. A circle with r= 0.714μm will have equivalent surface area to rod-like. | [http://redpoll.pharmacy.ualberta.ca/CCDB/cgi-bin/STAT_NEW.cgi University of Alberta] |
| Mass | 1.02x10-13g | MG1655 | Given 1x10-12g for cell wet weight. Dividing this by gravity (=9.81) gives mass. | [http://redpoll.pharmacy.ualberta.ca/CCDB/cgi-bin/STAT_NEW.cgi University of Alberta] |
| Swimming Speed | 50μms-1 | MG1655 | University Alberta's datasheet gives 50μms-1. However, Swimming speed is affected by:
Many papers give different and variable speeds (mainly for AW405 ~20μms-1). The speed itself is nearly uniform during the run. May need to measure experimentally, don't know under what conditions University of Alberta. Alberta value is higher than other values, but probably because MG1655 is a motile strain. | [http://redpoll.pharmacy.ualberta.ca/CCDB/cgi-bin/STAT_NEW.cgi University of Alberta], [http://www3.interscience.wiley.com/cgi-bin/fulltext/71003069/PDFSTART A Method for Measuring Bacterial Chemotaxis Parameters in a Microcapillary] |
Run Tumble motion
| Attribute | Value | Strain | Justification | Reference | |
| Aspartate concentration detected by E. coli | Over ~5 orders of magnitude, 10nM up to 10mM. Can detect changes of as little as ~0.1% | N/A | Most computer simulations of the chemotaxis pathway based on experimentally determined rates and concentrations predict a minimum detectable concentration of the attractant aspartate of around 200 nM. However, experiments performed by Segall et al. in 1986, in which E. coli cells are tethered to a coverslip were exposed to small quantities of chemoattractant delivered iontophoretically. These experiments indicated that a change in receptor occupancy of as little as 1/600 could produce an detectable change in swimming behaviour. With a Kd of 1 µM, this corresponds to a minimum detectable concentration of about 2 nM aspartate. E. coli cells can adapt to Aspartate concentrations over ~5 orders of magnitude. Wild type E. coli cells can detect <10nM of Asp and respond to gradients upto 1mM of Asp. detect small changes in concentration ( 0.1%) via temporal comparisons ( 4 s) over a large range ( 10-8 to 10-3 M) | [http://www.jbc.org/cgi/reprint/281/41/30512 Competitive and Cooperative Interactions in Receptor Signalling Complexes] | |
| Temporal comparison of chemotactic gradient | 4 seconds | N/A | The past second has positive weighting, the previous 3 seconds have negative weighting. E coli compares these concentrations (average occupancy of the receptors) and therefore the memory lasts approximately 3 s. Models reflecting this have been developed by Segall et al and Schnitzer, cells compare their average receptor occupancy between 4 and 1 s ago c 1–4 to the average receptor occupancy during the last second c 0–1. Hence b= c 0–1 - c 1–4, If b>0, the cell reduces the tumbling rate to Ttumb from the ambient value T0 (1s-1) e.g. b>0 don't tumble. b< tumble at a rate of 1s-1 | [http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=387059&blobtype=pdf Temporal comparisons in bacterial chemotaxis] [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TBN-4CVRC68-2&_user=121739&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=121739&md5=470c7fd73fb9ebf4ca43342f365e221f#sec5.1 Quantitative analysis of signalling networks][http://web.mit.edu/biophysics/papers/PNAS2003b.pdf Motility of Escherichia coli cells in clusters formed by chemotactic aggregation] | |
| Tumbling angle | Shape parameter 4 Scale parameter 18.32 Location parameter -4.6 | AW405 | Appears not to be dependant on the concentration gradient of chemoattractants/repellents. Nor is there correlation between the length of the run and the change in direction. Used a gamma distribution that fitted the data of Berg and Brown. Non normality observed by several groups. Suggestions that non-normality was only due to the experimental methods used e.g. in the capillary tube. Tumbling can cause a change in direction when as few as one filaments moves out of the bundle. The flagella on transition from the bundle to release go from normal (a left-handed helix with a pitch of 2.3 m and a diameter of 0.4 m) to semi coiled (a right-handed helix with half the normal pitch but normal amplitude) and then curly (a right-handed helix with half the normal pitch and half the normal amplitude). | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. coli anaylsed by three-dimensions] [http://bioinformatics.oxfordjournals.org/cgi/reprint/21/11/2714 AgentCell: a digital single-cell assay for bacterial chemotaxis] [http://jb.asm.org/cgi/reprint/189/5/1756 On Torque and tumbling in swimming Escherichia coli] | |
| Tumble angle direction | Bidirectional | AW405 | Personal communication with Howard Berg. 'The direction is random, more or less, but there is a slight forward bias. It varies from tumble to tumble. The turn-angle distribution peaks at 68 deg rather than 90 deg. Tumbles turn out to be more complex than believed in 1972. Motors switch independently, and a tumble can occur if one or just a few motors change their directions of rotation. Tumbles are short, as judged by the tracking microscope, because they involve filament physics rather than motor physics: a transformation in polymorphic form, following motor reversal, from normal to semi-coiled. See Darnton, N.C., Turner, L., Rojevsky, S. and Berg, H.C. On torque and tumbling in swimming Escherichia coli, J. Bacteriol. 189, 1756-1764 (2007).' | ||
| Tumbling time | 0.14±0.19s | AW405 | Exponential distribution fitted (stated to be exponential by Berg and Brown) using only the mean tumble length (not STDEV). | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking] | |
| Relationship between tumbling angle and time | |||||
| Speed while Tumbling | 0μm.s-1 | AW405 | Berg and Brown noted that AW405 slowed/stopped while tumbling. | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking] | |
| Drift during run | 23±23○ | AW405 | Drift was observed. It is what would be expected from rotational diffusion. (at 2.7cp at 32ºC drift was 23±23°). Rotational Brownian motion cause the cell to veer off course, so that in between tumbles the probability density function f of the swimming direction e evolves according to the Fokker-Planck equation. Drift velocity in steep gradient of attractant ~7 µm/s (Berg & Turner, 1990) | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking] [http://www.springerlink.com/content/d8u27q8430202342/ Persistence of direction increases the drift velocity of run and tumble chemotaxis] [http://www.pdn.cam.ac.uk/groups/comp-cell/Biophysics.html Bray computer modelling] | |
| Isotropic run lengths | 0.86±1.18s | AW405 | Exponential distribution fitted, this is only an approximate and does not fit exactly (see fig.4 Berg and Brown) The standard deviation is the standard deviation of the mean and has not been used in the exponential distribution | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking] | |
| Run length UP Aspartate gradient | 1.07±1.80s | AW405 | Exponential distribution fitted, this is only an approximate and does not fit exactly (see fig.6, Berg and Brown). The standard deviation is the standard deviation of the mean and has not been used in the exponential distribution Phenylalanine ( the recruitment chemoattractant) utilises a mutant of the Tar receptor. The mutant Tar receptor has been shown to have comparable chemotactic response to the wild type and therefore the values used for the run lengths of aspartate can also be used for phenylalanine. | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking][http://parts2.mit.edu/wiki/index.php/University_of_California_San_Francisco_2006 UCSF wiki] | |
| Run length DOWN Aspartate gradient | 0.8±1.38s | AW405 | Exponential distribution fitted, this is only an approximate and does not fit exactly (see fig.6, Berg and Brown) The standard deviation is the standard deviation of the mean and has not been used in the exponential distribution | [http://www.nature.com/nature/journal/v239/n5374/pdf/239500a0.pdf Chemotaxis in E. Coli anaylsed by three-dimensional tracking] | |
Swimming Machinery
| Attribute | Value | Strain | Justification | Reference |
| Average thrust | 0.41±0.23 pN | AW405 | 0.41±0.23 pN ( standard deviation for 32 bacteria) was obtained from strain AW405, a strain which has provided the majority of our previous parameters but is not MG1655 which is more motile. The value was obtained at 23ºC in viscosity 0.93 and 3.07 cP for motility buffer and motility buffer with 0.18% methylcellulose, respectively. The standard deviation is not used as the speed is fixed at 50µm/s. 0.57pN is the average thrust generated in strain HCB30 (a non tumbling strain). The thrust value was obtained when the imposed flow (U) U=0 at 23ºC. O.41pN was calculated using the resistance force theory treating the flagellar bundle as a single filament. The body was assumed to be prolate elipsoid using values roughly similar to ours, 2μm for length and 0.86μm for diameter. | [http://jb.asm.org/cgi/reprint/189/5/1756 On Torque and tumbling in swimming Escherichia coli] [http://www.pnas.org/content/103/37/13712.full.pdf+html Swimming efficiency of bacterium E. coli.] |
Properties of the media
| Attribute | Value | Strain | Justification | Reference |
| Viscosity | Viscosity of water is 1.002cP at 20○C | N/A | At present the medium being used by the lab is still be discussed. Currently though the medium most resembles water and therefore the water's viscosity value can be used. This allows us to assume that the medium is Newtonian (dilute aqueous medium that doesn’t contain long unbranched molecules such as methylcellulose or polyvinylpyrrolidone. Note that methlycellulose does not alter the run and tumble statistics, only bundle and motor rotation rates are affected by the addition of methylcellulose). If agar were to be used then the medium would be Non-Newtonian. Even though it would be Non- Newtonian John Hogan in passing said that we could assume it is Newtonian. | [http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.biochem.72.121801.161737 The rotary motor of bacterial flagella. Physica A 358 (2005) 205–211.] On torque and tumbling in swimming Escherichia coli |
| Diffusion coefficient of Aspartate. | 0.033 cm2.h-1 | N/A | 0.033 cm2/h is for aspartate at 22°C in 0.15% agar. Another value from the literature, 0.9 x10-5 cm2/s, is for aspartate at 35◦C in 0.3% agar. To calculate diffusion coefficients the following formula can be used D=RT/6πNvr where: R is the gas constant, T is the absolute temperature (Kelvin), N is the number of molecules in a mole (6 x1023), v is the viscosition of the solvent (e.g. 0.001 for water), r= radius of the particle. This formula could be used to calculate the diffusion coefficient at the viscosity used in our experiments. | [http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1300146&blobtype=pdf Chemotactic Responses of Escherichia coli to Small Jumps of Photoreleased L-Aspartate] [http://www.pnas.org/content/96/20/11346.full.pdf\" Response tuning in bacterial chemotaxis] |
| Diffusion coefficient of Phenylalanine. | 3.58 x 10-4 cm 2 min -1 | N/A | This value is for phenylalanine in aqueous phase at 25ºC. | [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TGK-3W38497-D&_user=121739&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000010018&_version=1&_urlVersion=0&_userid=121739&md5=316e71596cb388d2a0cf0de7c15f84fe#fd16 Extraction and re-extraction of phenylalanine by cationic reversed micelles in hollow fibre contactors] |
| Quorum Signal | OHHL (3-oxo-C6-HSL) | N/A | From the quorum sensing system of Vibrio Fischeri produced by LuxI. Molecular weight: 213 | |
| Basal (constitutive) rate of AHL production | 30nmol.hr-1 | V. fischeri | Value was used in a modelling simulation of the Lux system in V. fischeri. Note that the maximum [AHL] is achieved during stationary phase. | [http://docstore.ingenta.com/cgi-bin/ds_deliver/1/u/d/ISIS/45421751.1/ap/mb/2001/00000309/00000003/art04697/34CECEE65ADECE1112181237349BDA2365FA8246B1.pdf?link=http://bristol.library.ingentaconnect.com/error/delivery&format=pdf Kinectics of the AHL regulatory system in a model biofilmsystem: How many bacteria constitute a Quorum?] |
| Diffusion coefficient for Quorum signal | Daq= 4.9x 10-6 cm2 s-1 | N/A | Daq= 4.9x10-6cm2.s-1 is the diffusion coefficient of 3 oxo-C12 AHL in water, not OHHL as we would be using. Estimations can be calculated using Wilke Chang equation (see Perry\'s Chemical Engineers\' Handbook). De = 1.23x 10-6 cm2 s-1 is the effective diffusion coefficient of 3 oxo-C12 AHL in biofilm. | [http://www.springerlink.com/content/v36128k24t558820/fulltext.pdf The effect of the chemical, biological and physical environment on quorum sensing in structured microbial communities. Anal Bioanal Chem (2007) 387:371-380.] |
| Threshold concentration of autoinducer | Use imperial iGEM value 1nM! ~1 to 10μg.ml-1 | N/A | In the pattern formation paper fig 2c and d represent a simulation and experimental data respecitively. The graph plots the concentration of AHL required to elicit a visual response (observation of fluorescence). Imperial iGEM team looked at the lower and higher threshold levels of AHL in vivo and in vitro. They also visualised this with expression of GFP. Low threshold 1nM in vivo (estimated the number of plasmids present) in vitro value is only obtained on extrapolation and therefore it is not accurate but predicited to be higher. High threshold is ~1000nM and therefore beyond this level the system does not respond to any further increase, the system is saturated. See graph sheet. Another paper, A novel strategy for the isolation of luxl homologues:evidence for the widespread distribution of a LuxR:Luxl superfamily in enteric bacteria. The V. fischeri sensor for OHHL is very senstive requiring levels of 10ng.ml-1 to inititate transcription. This paper also states that the thresholds differ depending on strain of bacteria and cell densities. The Imperial\'s iGEM team value is the best as it is for MC1000 and therefore most relevent for this project. | [http://www.nature.com/nature/journal/v434/n7037/pdf/nature03461.pdf A synthetic multicellular system for programmed pattern formation.] [http://parts.mit.edu/igem07/index.php/Imperial/Infector_Detector/F2620_Comparison Imperial iGEM wiki][http://www3.interscience.wiley.com/cgi-bin/fulltext/119307663/PDFSTART A novel strategy for the isolation of luxl homologues: evidence for the widespread distribution of a LuxR:Luxl superfamily in enteric bacteria] |
| Protein decay (LuxR/AHL) | 0.0231 min-1 | [http://www.nature.com/nature/journal/v434/n7037/pdf/nature03461.pdf A synthetic multicellular system for programmed pattern formation.] | ||
| LuxR/AHL activation coefficient | 0.01µM | [http://www.nature.com/nature/journal/v434/n7037/pdf/nature03461.pdf A synthetic multicellular system for programmed pattern formation.] | ||
| LuxR/AHL dimerisation | 0.5µM-3.min-1 | [http://www.nature.com/nature/journal/v434/n7037/pdf/nature03461.pdf A synthetic multicellular system for programmed pattern formation.] | ||
| AHL decay | 0.01min-1 | Note that this value is affected by pH | [http://www.nature.com/nature/journal/v434/n7037/pdf/nature03461.pdf A synthetic multicellular system for programmed pattern formation.] | |
| Particle | 10µm diameter and round | Value obtained from lab team | Bacterial flagella-based propulsion and on/off motion control of microscale objects | |
| Particle density | 1.05g.cm-3 | N/A | Value is for the particles the lab team is using | |
| Diffusion coefficient of 10μm polystyrene bead | 4.93x10-14 m2/s | N/A | Bacterial flagella-based propulsion and on/off motion control of microscale objects | |
| Drag on 10μm sphere | 1.4pN | N/A | Bacterial flagella-based propulsion and on/off motion control of microscale objects | |
