This photo resembles a colorful flower. But you can see colonies of two different bacterial species that have arranged themselves in the nutrient medium in this amazingly flower-like shape.
In a nutrient medium, a microscopic bacterium quickly divides into a colony that is visible to us. The bacteria remain connected to one another after the cell splitting and thus form clusters of cells and branched cell chains. Depending on whether a bacterium is very mobile or not, differently shaped bacterial colonies develop.
This is also confirmed by our picture, which researchers working with Liyang Xiong took from the University of California in San Diego. To do this, they cultivated two different types of bacteria for 48 hours in the middle of a semi-solid nutrient medium that consisted of one percent agar gel. They colored the species in different colors to understand their movements and distribution.
One of the types of bacteria was Acinetobacter baylyi, which occurs in the soil and water and which typically moves quickly on agar plates with its “legs”, the pili. In addition, the scientists cultivated the intestinal bacterium Escherichia coli, which can move quickly in liquids with its flagella, but only with difficulty on solid surfaces.
The result: The cell associations of the species were arranged differently from the center of the Petri dish, so that this artistic, floral pattern emerged on our picture. It was interesting, however, that the red colored, motile Acinetobacter species primarily arranged in the center of the Petri dish. The green-colored E. coli bacteria, which are difficult to move in the semi-solid nutrient medium, on the other hand, were scattered around the edge zone.
According to the researchers, this distribution could be related, among other things, to the fact that the highly motile Acinetobacter cells “hitchhiked” the E. coli bacteria and were able to spread. Through this interaction and also through friction between the bacteria, the E. coli bacteria were apparently able to move to the edge of the Petri dish in order to get nutrients there, speculate Xiong and her colleagues.
“These findings can help us to understand the origins of the complex structures that are observed in many naturally occurring bacterial communities,” the research team sums up.