How does nutrient media affect color variation in Serratia marscesens?
Serratia marscesens is a pathogen bacterium that can be found in hospital-acquired infections and that appears in some humans tracts. If you do not know about it, think that its color is so much alike the human red blood color that there is an old middle age legend that tells us that prodigiosin - the Serratia marscesens pigment - has been evoked as a naturalistic explanation of a miraculous appearance of blood on the Corporal of Bolsena, a consecrated host that was thought to be the blood of Christ!
Anyway, the metabolism and the functioning of this bacterium is still quite unknown, and by studying prodigiosin’s role and activities we could find more informations about its importance in the microbe and therefore provide more basic knowledge to look for medical cures. In the study of it, we can change different parameters to look at its color variation. I decided to study the influence of nutrient media as it was easier to manipulate in the laboratory than other parameters (pH, Temperature…) and because if the results have significance, the research of nutrient media's influence on bacteria in a more general way could be applied in other researches!
Pictures: you can see there the reaction of prodigiosin on bread, and see how much does it look like blood! Then, a picture of a tapestry depicting the Miracle of Bolsena in a parade in Orvieto, Italy.
Looking for bibliography, I found there were already some researches that studied the effect of some nutrient media on prodigiosin color variation. They showed the red color tended to decrease in stressful conditions, which means that Serratia marscesens can show a wide range of colors going from light red to white!
I used a new nutrient media: PCA. This one is a normal nutrient media used to grow bacteria in the lab. I just decided to change the quantity of trypton - the main source of nutrients - and see how the colonies behaved after some time of incubation at an optimal growth temperature.
So here you can see my results. In the x-axis there are the different quantities of trypton I added in the different nutrient media (0g, 0.5g, 1g, 2g, 4g). In the y-axis there is the reference I used to study the color intensity of my colonies with a software called ImageJ. The more the values are high, the more the color get lighter! Starting from the O.5 g, that is the normal quantity of trypton in PCA, you can see that the more I add trypton the more the color values tend to increase, and so the color get lighter! Keep in mind that all the points are simple averages of all the data I collected for my replicates. What you can finally observe, is that the only point that does not follow this increasing pattern is the last one. I don’t have enough data to see if this behaviour will continue by adding more and more trypton, but it would be definitely worth studying it in further researches!
Finally, I can conclude with these results that Serratia Marscesens effectively do behave as other researches observed in their studies on other nutrient media effects on the microbe: in stressful condition of media, the color tends to decrease. Now, the experiment would need to be repeated more than once to see if - as my experiment has shown - the color of the bacterium does really start to get darker again at a certain quantity of trypton added. And if this is the case, try to find new hypothesis on why this phenomenon happen and then create new protocols and do new experiments to observe this color variation!
Sarah Talon Sampieri, student at Licence Frontières du Vivant, Université Paris Descartes.
This post is based on a project experience made in Petnica Science Center, for the program #labsprint
If you want to know more, here you are some pages and video:
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