Hi folks :)
As midnight approaches, I'm asking myself how I putted myself in this situation where I have to write a blogpost, late at night, about some research I have done in Petnica, a serbian scientific center lost in the countryside. And I think that I actually enjoy sharing my experience with you guys but let's get sciency and start to focus on our story.
Introduction to prodigiosin :
I had to find a topic, a scientific question that I wanted to address, to experiment about and it wasn't something easy to find. Looking at some petri dishes that we plated days before, I noticed strong red spreaded over the plate. I was looking at bacteria Serratia marcescens producing pigments and I started to think : Having a synthesis pathway to produce a pigment must be energetically costing. So why would this ability being kept over generations if it's not giving some advantage in counterpart ?
So I started to search in the literature and I found out that this pigment, actually called prodigiosin, has some antifungal and antibacterial properties. I wanted to know more about prodigiosin and if it was responsible for an interferential competition in between S.marcescens and other Enterobacteriaceae. In other words : Is the production of prodigiosin giving S. marcescens an advantage against other bacteria sharing its ecosystem inducing S. marcescens domination ?
How to crack the solution of the problem :
To find out about prodigiosin effects on other bacteria, I chose to test it on Escherichia coli as they are also Enterobacteriaceae and can be found in our guts just as S. marcescens. In a second time, I needed to have access to prodigiosin since I wanted to measure its specific effect, getting rid off all the biological noise provided by a living S. marcescens proliferating nearby. For the prodigiosin extraction, I decided to sonicate the cell, meaning use ultrasounds to create cavitation bubbles in the liquid breaking/cracking cell membranes, killing the cells and releasing the pigment in the media. 
Here are more details about my protocol for interested ones ;)
I had two solutions, one containing prodigiosin (pig) and another without it (Øpig) that I applied on E. coli and Saccharomyces cerevisiae cultures. S. cerevisiae was my positive control since the antifungal effect is known and admitted. So if no effects on S. cerevisiae were observed, the sonication process might had destroyed the prodigiosin and that’s why no effects would have been observed on E. coli.
Answer me !
About my results, I discovered that the S. marcescens in my solutions pig and Øpig weren’t dead and they started to proliferate on the E. coli and S. cerevisiae cultures. Nevermind, research is apparently never going well at first time when you’re testing new stuffs. However, S. marcescens took over both cultures ! Even if they were weakened by centrifugation and sonication. That’s why I decided to count how many Serratia marcescens I had in my pigmented and nonpigmented solutions.
Here are the results I obtained the day after :
Fig. 2 : 1 stands for E. coli culture and 2 for S. cerevisiae culture. Blue and green dots are the E. coli test and its replicate. Same for red and yellow dots but for S. cerevisiae.
As I observed 24 hours after, the cell concentration was much higher in the cultures where pig solution was applied compared to those of Øpig in both E. coli and S. cerevisiae.
End of my journey… but maybe start of yours ?
I discovered that 2 x 60 seconds of sonication is not enough for killing Serratia marcescens and I want to improve my protocol by sonicating for 7 minutes long as newly found literature adivises. Killing the bacteria and getting the prodigiosin out of the cells would allow more precise testing and better conclusions. We can even think of purifying the prodigiosin but it is much more complex. Overall, results showed that S. marcescens vigour is correlated with the presence of prodigiosin, making it easier to take over competing bacteria. But be conscious that correlation doesn’t mean causality, I need further experiments to conclude so.
And that was it, I hope this blogpost gave you some ideas or interests about prodigiosin. Since it has some really cool properties, its popularity among searchers is rising. If you want to know more about it and become a prodigious (searcher) in cancer or infection treatment, here are some materials to start with. Enjoy !
By Nikola Zarevski
L2 FDV Student Bachelor
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