Difference between revisions of "Team:Marburg/Measurement"

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            F A C S
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Fluorescence Activated Cell Sorting (FACS) is a flow cytometry measurement technique that separates single cells with different fluorescence characteristics. In this method you get accurate measuring results, because every single cell is analyzed on its own. FACS analysis can be used for cell sorting, fluorescence analysis of single cells and cell counting of different sample mixtures.<br>
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In flow cytometry, the sample with the cells get hydrodynamically focused in a single stream. The cells arrange in a row, so that they can pass a laser one by one. The cells get excited by the laser and emit light at various wavelengths, which is then detected by a fluorescence analysator. The detector can detect and separate different fluorescence intensities at a definite range of wavelengths. Through this cells can be categorized by different fluorescent characteristics and if wanted separated into defined categories by a deflection system using electromagnetic fields. <br>
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Furthermore, it is possible to determine the cell volume and size, as well as to distinguish between different kinds of cells, particles or cell clumps. For this, there are scatter detectors around the capilar. A forward scatter detector (FSC) and a stream side scatter detector (SSC) are placed around the stream.<br><br>
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<h2>Flow cytrometry for growth curves</h2>
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With the flow cytometry device available to us we were able to capture highly accurate cell counts. This brought us the idea of implementing this technique in a way less related to fluorescent reporters: counting cells in our cultures to capture growth curves instead of relying on optical density measurements. <br><br>
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Measurements of optical density are highly influenced by a multitude of factors. When measuring samples it is common to receive different results every time the same sample is measured, as in the meantime the distribution of cells inside of the probe has changed - mainly due to them slowly sinking to the bottom of the cuvette while not being shaken. This leads to high measurement errors. <br><br>
 +
Cell counts offer a promising alternative, as they are independent of factors that could influence OD measurements: impurity in the probe can distort OD measurements, while in flow cytometry the polluting particles will mostly be clearly distinguishable from the other counts. Especially with cyanobacterial cultures this can be used as a huge advantage: the autofluorescence of the cell gives us a clear way to select for the right event counts in our device, which we can then gate in order to receive just the number of cells with the fitting fluorescence signal.<br><br>
 +
In order to construct an actual growth curve out of this, another important part is needed: counting beads. <br>Those beads emit a distinct fluorescent signal that can be clearly detected and distinguished from other events. Using different filters we can select for the fluorescence we want to look at, one of them being the one of the beads and the other one from our cyanobacteria. The event number of the counting beads can now be used to determine the exact number of cells in the culture - this is how it works:<br>
 +
One counts the beads and sets a fixed number as the stop-criteria, meaning that the event count will stop after a certain amount of beads has been counted. Afterwards one can look at the number of cyanobacterial cells that have been counted in the same time the fixed amount of beads has passed and can calculate back to the whole culture volume in order to determine the amount of cells in the culture using the following formula:<br><br>
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A/B x C/D=concentration of sample as cells/µL<br>
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Where:<br>
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A = number of cell events<br>
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B = number of bead events<br>
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C = assigned bead count of the lot (beads/50 µL)<br>
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D = volume of sample (µL)<br><br>
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As one can already see from the formula, usually 50µl of beads are added to each sample that is run through the flow cytometer. This allows for accurate comparability.<br>
 +
Figure 1 shows our setup for the measurement of growth curves. The gated beads are counted to an event number of 1000. Meanwhile our cells are counted in a defined gate reaching from 2x10^3 to 10^5 relative fluorescence units. For detection of autofluorescence the APC filter was used. APC stands for Allophycocyanin, as this filter is designed to show the fluorescence of excited Allophycocyanin from red algae - a protein similar to phycocyanin in cyanobacteria, which is the reason why this setup works well to show cyanobacterial autofluorescence.<br><br>
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  <img src="https://static.igem.org/mediawiki/2019/f/f2/T--Marburg--CellCountSetup.png" alt="CellCountSetup">
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    Fig.1 - Setup for the creation of growth curves through cell counts with flow cytometry.
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Revision as of 02:16, 22 October 2019

M E A S U R E M E N T

Amplifying new standards in measurement

Vielleicht noch ein allgemeinem abstract zu Messung (vergleiche andere WIKIS)

Storytelling:

We entered this project as the first Marburg iGEM team working with Synechococcus elongatus UTEX 2973, the fastest phototrophic organism. Missing knowledge in handling and cultivation of UTEX 2973 left us in front of many problems and questions. Especially the usage of different media, light conditions and other cultivating and measurement parameters were one of the biggest problems we discovered in scientific papers. Many of these problems are reasoned in the ongoing optimization and development of methods and instruments. Therefore it is hard to hold on to special methods but still standardization is a huge part in synthetic microbiology and necessary to compare results with other scientists and reproduce their data.

While we wanted to establish Syn. elong. as a new chassis for the iGEM community and scientists we wanted to show the best conditions for cultivation and the best measuring method for our parts in UTEX 2973. Therefore we analyzed a big variety of cultivating conditions in measuring growth curves, tried to find a standard in light measurement, evaluated different reporters???, established a measurement method and compared it to a already known FACS measurement method (?).

At the beginning of our project we faced the first question on how to cultivate UTEX at 1500 μE. [quelle]. So we had to measure the light conditions in our incubators and while doing this simple task the first part of standardization began. We discovered that nearly every paper? is using different methods to measure their light conditions and that it is a really complex and important procedure. So we got in contact with cyano and light measurement experts [link IHP] to confront this problem and standardize it. In the following popup we show different ways of measurement, their (dis-)advantages and different results depending on the measuring instrument.
Not only the light intensity but also a variety of other cultivating parameters needed to be analyzed. In literature and while talking with different experts (IHP), we recognized that small deviations of these parameters had a huge impact on the growth speed of Synechococcus elongatus. While establishing UTEX 2973 as a new chassis we evaluated this impact on the growth speed and were able to show combinations of parameters that lead to the fastest growth speed.
Another aspect was measuring the expression and characterize our part. Different possibilities were discussed and after testing them we decided on two methods in our project (plate reader and FACs). One approach was to measure the fluorescence/luminescence with a plate reader [link part measurement]. Plate readers belong to standard equipment of every lab nowadays, and could deliver easy reproducible results.
The second way was to measure the fluorescence by FACS (Fluorescence-Activated Cell Sorting) [link facs]. In contrast to a platerader a FACs device delivers results with high accuracy by measuring every cell by its own(vielleicht erst spaeter FACS genau erklaeren aber nicht im abtract?). On the other side not every laboratory posses a FACs/device. So in the end we would like to offer a two method analyzed database from our crontructs for iGEM teams and research groups, who do not have access to a FACS and show the difference in measurement methods.
At the end of the project we were able to create a protocol how to handle Synechococcus elongatus UTEX 2973 and make a contribution to the cyano community by establishing essential/fixed standards in measurement.

L I G H T
M E A S U R E M E N T

Hier bitte den für diese Stelle zutreffenden Text einfügen, wenn dieser fertig ist.

R E P O R T E R S

Hier bitte den für diese Stelle zutreffenden Text einfügen, wenn dieser fertig ist.

F A C S

Fluorescence Activated Cell Sorting (FACS) is a flow cytometry measurement technique that separates single cells with different fluorescence characteristics. In this method you get accurate measuring results, because every single cell is analyzed on its own. FACS analysis can be used for cell sorting, fluorescence analysis of single cells and cell counting of different sample mixtures.
In flow cytometry, the sample with the cells get hydrodynamically focused in a single stream. The cells arrange in a row, so that they can pass a laser one by one. The cells get excited by the laser and emit light at various wavelengths, which is then detected by a fluorescence analysator. The detector can detect and separate different fluorescence intensities at a definite range of wavelengths. Through this cells can be categorized by different fluorescent characteristics and if wanted separated into defined categories by a deflection system using electromagnetic fields.
Furthermore, it is possible to determine the cell volume and size, as well as to distinguish between different kinds of cells, particles or cell clumps. For this, there are scatter detectors around the capilar. A forward scatter detector (FSC) and a stream side scatter detector (SSC) are placed around the stream.

Flow cytrometry for growth curves

With the flow cytometry device available to us we were able to capture highly accurate cell counts. This brought us the idea of implementing this technique in a way less related to fluorescent reporters: counting cells in our cultures to capture growth curves instead of relying on optical density measurements.

Measurements of optical density are highly influenced by a multitude of factors. When measuring samples it is common to receive different results every time the same sample is measured, as in the meantime the distribution of cells inside of the probe has changed - mainly due to them slowly sinking to the bottom of the cuvette while not being shaken. This leads to high measurement errors.

Cell counts offer a promising alternative, as they are independent of factors that could influence OD measurements: impurity in the probe can distort OD measurements, while in flow cytometry the polluting particles will mostly be clearly distinguishable from the other counts. Especially with cyanobacterial cultures this can be used as a huge advantage: the autofluorescence of the cell gives us a clear way to select for the right event counts in our device, which we can then gate in order to receive just the number of cells with the fitting fluorescence signal.

In order to construct an actual growth curve out of this, another important part is needed: counting beads.
Those beads emit a distinct fluorescent signal that can be clearly detected and distinguished from other events. Using different filters we can select for the fluorescence we want to look at, one of them being the one of the beads and the other one from our cyanobacteria. The event number of the counting beads can now be used to determine the exact number of cells in the culture - this is how it works:
One counts the beads and sets a fixed number as the stop-criteria, meaning that the event count will stop after a certain amount of beads has been counted. Afterwards one can look at the number of cyanobacterial cells that have been counted in the same time the fixed amount of beads has passed and can calculate back to the whole culture volume in order to determine the amount of cells in the culture using the following formula:

A/B x C/D=concentration of sample as cells/µL
Where:
A = number of cell events
B = number of bead events
C = assigned bead count of the lot (beads/50 µL)
D = volume of sample (µL)

As one can already see from the formula, usually 50µl of beads are added to each sample that is run through the flow cytometer. This allows for accurate comparability.
Figure 1 shows our setup for the measurement of growth curves. The gated beads are counted to an event number of 1000. Meanwhile our cells are counted in a defined gate reaching from 2x10^3 to 10^5 relative fluorescence units. For detection of autofluorescence the APC filter was used. APC stands for Allophycocyanin, as this filter is designed to show the fluorescence of excited Allophycocyanin from red algae - a protein similar to phycocyanin in cyanobacteria, which is the reason why this setup works well to show cyanobacterial autofluorescence.

CellCountSetup
Fig.1 - Setup for the creation of growth curves through cell counts with flow cytometry.