Experimental evolution of kin discrimination types in Bacillus subtilisBelcijan Pandur, Katarina (Avtor) Mandić Mulec, Ines (Mentor) Bacillus subtilisinteractionskin discriminationexperimental evolutioncompetence for transformationantagonismcooperationDNA exchangeswarmingsurfactinBacillus subtilis is a widespread environmental bacterium capable of kin discrimination during swarming, whith swarms of closely related kin strains merging, while non-kin swarms form strong boundaries. B. subtilis is also able to take up extracellular DNA through competence for transformation. Stress response has been shown to increase the transformation frequency of B. subtilis cells in liquid cultures. Observing activation of stress responses during antagonistic non-kin interactions on swarming agar, we hypothesized that such interactions might promote DNA exchange between non-kin B. subtilis swarms. Our work demonstrates that kinship-dependent interactions among B. subtilis isolates cause envelope stress in the attacked strain, which upregulates the competence in the attacker and facilitates DNA exchange between non-kin swarms. We further examined whether non-kin interactions influence the evolution of divergent kin discrimination (KD) phenotypes. Although no conclusive evidence was found in relation to kinship dependent influence, divergent KD phenotypes emerged and spread more frequently in non- competent populations compared to competence-proficient populations, which denotes the importance of competence in DNA repair and the maintenance of phenotypic traits. The third objective of the thesis was to test whether non-kin encounters limit the spread of exploiters in adjacent populations during surfactin-dependant cooperative swarming over surfaces. Results showed that by mixing surfactin-producing cooperators and surfactin exploiters at 1:1 initial ratio, the cooperative swarming quickly collapses. However, when experimental populations were repeatedly exposed to non-kin or kin swarms, the former were less likely to carry non-swarming clones. This suggests that non-kin encounters constrain the spread of surfactin exploiters and that non-kin attack during swarms’ encounter may influence the stability of cooperation. Overall, our results highlight the importance of social interactions in bacterial evolution and suggest that horizontal gene transfer may play a dual role: promoting adaptation to novel environments while also supporting DNA repair to maintain phenotypic stability. This interplay between genomic plasticity and stability appears to be of central importance to bacterial survival and evolutionary dynamics.[K. Belcijan Pandur]20252025-04-10 07:15:16Doktorsko delo/naloga168343UDK: 579.22/.26:579.852.11VisID: 257237COBISS_ID: 232196099sl