Curvy Shapes
Franck Porteous
Introduce the 3 days project
During summer 2016, The Fdv bachelor give us the chance to participate at the microbiology seminar in Petnica. We had the opportunity to conduct a personal project closely linked to microbiology. I’ve chosen to focus on a observation experiment, using the method I learned days before I’ve been able to create this project. The observation of the shapes forming by a colony of Serratia Marcescens (we called a colony a eye-observable aglomerat of cell born from a single cell, in my case I had chosen the S. Marcescens).
Having a better knowledge of the shapes of the colony lead to a precise approximation of the volume of a colony. Knowing the volume of a single bacterium, we could easily find the size of the studied population.
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Cut of a colony view by profilHow doing such thing ?
In my experiment the time was a precious resource, I chose to focus on one specific strain of bacteria having both a rapid growth rate and a “curvy” shape instead of fungi growing faster (not all of them) but flater. All the condition were optimal for this strain, in order to produce bigger colony in a small amount of time. All the sampling sections were spaced between 12 hour in the interest of observing a significant changement of shape. We know that a cell take in average 40 - 50 minute to make a duplication in this kind of condition.
In the "Lab"
Firstly I had to place all the bacterium homogeneously on the surface of the petri dish, then the plates were placed in the incubator at 37°C. I did three differents dilutions so i could produce differents kinds of densities of colony on the plate, later when the colony will be larger, high dilution plate will offer a choice of isolated colony which is the perfect sample for the rest of the experiment.
The sample consist of the prelevement of a single colony with the media underneath, then cut the thinness slice of this square to observe it under a optical microscope at x40. Then by taking picture of this observation with a camera (sony a6000) and a scale.
Cut of the media square
Analyse and understand the data
I was able to quantify the height of the colony at the edge and center following an interval (determined) based on the diameter of the colony itself.
Once the quantification was done with ImageJ (Fig.5), I’d transferred all the data on Plotly to make a graphical representation of the colony, viewed by profil. I chose to represent with dots and lines all the datas revolted, the bars represent the average height of the five sample I took (Fig.6). By taking interval for the measure based on the diameter of the colony, I did a first normalisation.
That means in the two independent variables I chose to normalise the diameter in order to focus only on the height, which is the main purpose of my project. Following the same pattern, I made a second graph (Fig.7) representing two average height of five colony space by 12 hours of incubation.
Conclusion and graphical results
By looking at those graphs, we can observe that the colony grew in height during time but lost they’re pointy pyramids profile. The oldest colony are higher and flatter.
A mathematical model of those shapes would give us the opportunity of determine precisely the future shape of a your growing colony in fonction of is external condition.
There is another case that we have to take in account. We know thanks to research already done that the older cell in the middle of a colony tend to die because of a lack of food. I've expected to find a crater in the middle of the colony (a dead bacterium take less place), sadly my method do not provide a point of view allowing the observation of this phenomena.
Are my data changed by this event ? No, in the small amount of time that had it's was nearly impossible to find any crater in the colony due to cell death.
Acknowledgment
I'd like to thank all the teething team and my tutor especially, all the facilities that make this seminar a reality and the bore promotion.
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If you want to go further ..
- Bacterial body plans Colony ontogeny in Serratia marcescens
- Colony shape as a genetic trait in the pattern-forming Bacillus mycoides Carmen Di Franco, Elena BeccariEmail author, Tiziana Santini, Giuseppe Pisaneschi and Giorgio Tecce http://bmcmicrobiol.biomedcentral.com/articles/10.1186/1471-2180-2-33
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