Team:TU Dresden/Project/Communication
Short Description
Peptidosomes can be a powerful co-culture technique to physically separate bacterial populations without limiting their ability to communicate with each other by exchanging signalling molecules. This part of EncaBcillus is focused on proofing the concept of communication between encapsulated bacteria by using the regulatory system for competence development in Bacillus subtilis which is based on quorum sensing.
Background
In order to solve complex tasks, it is reasonable to break down a problem into small subunits that can be addressed by specialists individually. This concept is widely implemented in modern economy but can also be applied to synthetic biology [1]. In nature, such strategies have been evolved over millions of years. A good example is the formation of biofilms by the gram-positive bacterium Bacillus subtilis (B. subtilis). Here, cell-cell interactions lead to cellular differentiation processes and thus enables an effective division of labour [2]. However, the development of synthetic consortiums consisting of several different bacterial strains, with each executing distinct tasks remains challenging [3].
By encapsulating subpopulations within molecular cages, called Peptidosomes, we want to physically separate co-working bacteria while still assuring their cooperativity to fulfil one major task. In this context communication between the bacteria is indispensable, thus we had to make sure that the Peptidosome membrane is permeable for small molecules and that the bacteria are still able to interact. In this part of EncaBcillus we will show that the encapsulation of one population does not limit its ability to communicate with cells in the surrounding medium.
The regulatory system for competence development in B. subtilis
Communication between encapsulated bacteria and bacteria in the surroundings
Based on this genetic background, we wanted to set-up a simple experiment that shows communication between two B. subtilis strains. The basic idea is comparable to a radio broadcast: you need a transmitter that sends out the radio waves and a receiver that receives the waves and convert them into an acoustical signal. Transferred to our project this means that we need a sender strain (SeSt) that secretes the ComX pheromone, and a receiver strain (ReSt) that reacts to the ComX-stimulation by producing an easy-detectable output (figure 2).
In our case, we fused target promoters of the competence machinery of B. subtilis to the lux operon and measured luminescence output. Additionally, the ReSt needed to be comX-deficient to prevent autoinduction. We encapsulated the ReSt within Peptidosomes and incubated it together with the SeSt in the surrounding medium. Thus, we expected ComX that is produced outside the Peptidosme to diffuse through the membrane and stimulate the ReSt. As a result, the luminescence signal should be restricted to the Peptidosome.
Image: Experimental setting: Peptidosome with ReSt and SeSt in surrounding medium, schematic by AnastasiaL Fig. 2: Co-culture of the receiver strain (ReSt) and the sender strain (SeSt) using Peptidosomes. The ReSt in the surrounding medium secretes the ComX pheromone and stimulates luminescence of the encapsulated SeSt via quorum sensing.
