Microbes cooperate with each other in the utilization of nutrients from the environment, mobility, virulence, iron accumulation, mutual protection, etc. The ability to identify related organisms (`kin`) and / or discriminate less related (‘nonkin’) is important for the evolutionary success of cooperation. As part of the master's thesis, we observed the swarming pattern of more or less related mixtures of Bacillus subtilis strains on semi-solid agar medium. If the two bacterial strains are not related / compatible, antagonistic interactions and competition for surface colonization occur. In our experiments `kin` and `nonkin` interactions between different fluorescently labeled (YFP or mKate2) strains of B. subtilis were observed under the stereomicroscope with fluorescent filters. We confirmed that, when occupying the surface, the mixture of `kin` strains forms joint swarms, whereas in the `nonkin` strain combination the strains are mutually exclusive; in most cases only one of the two strains can be detected. The ratio between the ‘nonkin’ strains in the initial mixture determines which strain will swarm more successfully on the surface. In some cases, we have detected segregation or spatially separated swarms of two `nonkin` strains on agar plate. The incidence of segregation increased when the initial inoculum of the cell mixture was diluted. Mutation in the comQ gene, which plays an important role in quorum sensing, does not affect the ability to form a common swarm with PS-216 wild type strain. Moreover, mixing the PS-216 comQ mutant with a `nonkin` strain indicated even greater efficiency of the mutant strain to colonize the surface as compared to its wild type.
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