In the environment, bacteria appear in the form of multicellular structures that are the product of complex intercellular social interactions. An important type of intercellular communication is quorum sensing (QS), which in B. subtilis is based on the ComQXPA system. The aim of the thesis is to investigate social interactions, namley quorum sensing, at the single cell level. To achive this, we aimed to optimize microfluidic device with 2D growth chambers in which B. subtilis cells grow and communicate through ComX dependent quorum sensing that regulates the experssion of the srfA operon. Our results show that growing B. subtilis PS-216 in CM medium, with a flow rate of 3 μL/min is more suitable than at the flow rate of 6 or 0.3 μL/min, because the cells were retained in the chambers and biofilm did not form in side chanels. Interestingly, under these conditions, the biomass in the growth chamber increased in intervals, with two intermediate "lag" phases during 42.5 hours experiment. We also monitored the fluorescence intensity of the PsrfA-YFP reporter as an indicator of the cellular response to ComX. The QS response was detected already at 3h after inoculation (signal measured around 640 r.f.u.) but incerased with the increase of biomass after 30 hours of incubation (signal measured around 1300 r.f.u.). As part of the master's thesis, we successfully optimized the preparation of microfluidic chips from PDMS and the management of the process in the microfluidic system, which is important for the quality performance of experiments in which individual cells are monitored over time. In addition to the optimization of the process, we also confirmed our hypothesis that the strength and time interval of the response to the ComX signal depend on the flow rate and the type of culture medium.
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