Is there any competition between two microbes in food-restricted environment?

Is there any competition between two microbes

in food-restricted environment?

Competition in biology refers to an interaction between organisms or species which often leads to conflict between them due to resources supply, space, or many other factors … This competition can occur as between members of the same specie as between members of two different species

For whatever reason, competition is one of the most important interaction occurring in nature and take such a large importance in ecology since it affects community structures and ecosystems.

Several types of competition subsist in ecology such as “exploitative competition” often referred as food competition but also “interference competition” in which individuals of one specie interacts directly with individuals of another specie with more aggressive behaviour in the aim of becoming predominant towards the other.

This study is very interesting since it allows us to focus on competition between two simple micro-organisms from the same type of environment (digestive system, human and rodent one) which are Escherichia coli (white colour) and Serratia marcescens (red colour) and try to see what append in this situation, if competition there is and which type.

In order to answer this question, I managed to prepare two different initial bacteria cultures in order to let them grow individually. Then, I prepared different environments with five different food quantities (under the form of glucose, a sugar) but still limited where I put either the two microbes or each microbes individually, these latter enabling to see how microbes react individually in the same environment conditions (we call this “negative control”). After a while in this environment suitable for competition, I diluted solutions of bacteria cells to keep enough quantity of cells but not too much that will enable me to observe them on “plates” where they will form colonies (a large amount of cells with the same genetic information, as we can see on the first picture above). As for quantification, I decided to focus on number of colonies (in mixed bacteria environment) and their size (between mixed and individual bacteria environment).

In order to answer this question, I managed to prepare two different initial bacteria cultures in order to let them grow individually. Then, I prepared different environments with five different food quantities (under the form of glucose, a sugar) but still limited where I put either the two microbes or each microbes individually, these latter enabling to see how microbes react individually in the same environment conditions (we call this “negative control”). After a while in this environment suitable for competition, I diluted solutions of bacteria cells to keep enough quantity of cells but not too much that will enable me to observe them on “plates” where they will form colonies (a large amount of cells with the same genetic information, as we can see on the first picture above). As for quantification, I decided to focus on number of colonies (in mixed bacteria environment) and their size (between mixed and individual bacteria environment).

This graph is part of my results and represents ratios of A/B numbers colonies in mixed bacteria plates according to the glucose concentration (A being E. coli and B being S. marcescens). We can see that there is a considerable number of S. marcescens colonies towards E. coli ones since the ratio is clearly lower than 1 except for the least concentration of glucose where this value is more important (due to error manipulation).

Other results concerning surface areas of colonies tend to show that E. coli colonies seem to be bigger when they’re alone unlike when they’re confronted to S. marcescens whereas S. marcescens colonies tend to be bigger when they’re confronted to E. coli unlike when they’re alone.

Thus, we can say that predominance of S. marcescens is shown in mixed plates and for all concentrations of glucose, gaining colonies surface area while exposed to E. coli, whose colonies are conversely bigger in negative controls.  Nevertheless, we have to take into account the lack of replicates (when we repeat the experiment) due manipulation problems that certainly impacts the reliability of my results. Furthermore, we have to be clear that I can’t prove any competition between microbes but maybe assume that there are at least interactions that led to the possible predominance that I just spoke before.

So, what would be good to do next is first and overall to repeat the experiment with replicates to have more reliability of the results. Secondly, it would be very interesting to work at the microscopic scale to have more criteria to quantify that will bring enough information about competition of microbes.

If you want to know more, here are some bibliography links to have more details about key aspects of my project and information that helped me to do it:

- Utida, S. (1953). Interspecific competition between two species of bean weevil. Ecology, 34(2), 301-307.

- Competition in biology information on Wikipedia

https://en.wikipedia.org/wiki/Competition_(biology)

v   

             - Interspecific competition information on Wikipedia

https://en.wikipedia.org/wiki/Interspecific_competition

  

             - Competition exclusive principle information on Wikipedia

https://en.wikipedia.org/wiki/Competitive_exclusion_principle

v            - Scramble competition information on Wikipedia

https://en.wikipedia.org/wiki/Scramble_competition

v           - Yoon, H., Klinzing, G., & Blanch, H. W. (1977). Competition for mixed substrates by microbial populations. Biotechnology and Bioengineering, 19(8), 1193-1210.

v            - E. coli information on Wikipedia

https://en.wikipedia.org/wiki/Escherichia_coli

v            - S. marcescens information on Wikipedia

https://en.wikipedia.org/wiki/Serratia_marcescens

v                  - Chramostova, J., Mošnová, R., Lisova, I., Pešek, E., Drbohlav, J., & Němečková, I. (2014). Influence of Cultivation Conditions on the Growth of Lactobacillus acidophilus, Bifidobacterium sp., and Streptococcus thermophilus, and on the Production of Organic Acids in Fermented Milks. Czech J. Food Sci, 32(5), 422-429.

v            - Thayer, D. W., Muller, W. S., Buchanan, R. L., & Phillips, J. G. (1987). Effect of NaCl, pH, temperature, and atmosphere on growth of Salmonella typhimurium in glucose-mineral salts medium. Applied and environmental microbiology, 53(6), 1311-1315.

Here, you will find the poster of my project in the framework of Petnica research projects week in Serbia with Paris Descartes university, CRI Paris and Schueller Bettencourt Fondation :  

Acknowledgements

All the teaching team of Petnica, all Bore students.

T. Milosevic for all advices, support, pedagogy and experience in Petnica Science Center.

G. Baudrin for his support and follow all along research projects as tutor.

Petnica Science Center for having given all these opportunities during the stay

Corentin Mathé - - Deletang
L2 FDV Bachelor
Paris Descartes & CRI PARIS