20.500.12556/RUL-173742 Role of TisB protein in protecting Escherichia coli against colicin E7 and bacteriophage T4 Vloga proteina TisB pri zaščiti bakterije Escherichia coli pred kolicinom E7 in bakteriofagom T4 Bacteria use various strategies to survive in stressful environments. In Escherichia coli (E. coli), DNA damage caused by antibiotics such as trimethoprim (TMP) and mitomycin C (MMC) triggers the SOS response, which activates the tisB gene. The TisB protein is a small toxin that damages the cell membrane and reduces the proton motive force (PMF), which affects bacterial survival and how cells respond to their environment. This thesis investigates how TisB affects the survival of E. coli after treatment with TMP or MMC, its role in defence against colicin E7, and its effect on infection with bacteriophage T4. Wild-type (WT) and ∆tisB strains were compared by measuring survival under varying concentrations of MMC or TMP, the extent of membrane depolarisation, and survival outcomes in environments with the colicin E7-producing strain BZB2110. The results show that TisB-induced depolarisation affects survival in an antibiotic-dependent manner and can either protect against colicin E7 by reducing membrane transport, or limit the import of nutrients necessary for survival. In addition, the effect of TisB on bacteriophage T4 infection was examined by measuring burst size with and without prior SOS induction, and the ∆tisB strain exhibited larger burst sizes compared to the WT strain. However, this difference may be due to other factors and is not necessarily a consequence of lower viral entry into depolarised WT cells. The results obtained provide a better understanding of the complexity of bacterial defence systems and their role in survival in competitive environments. Bakterije za preživetje v stresnih okoljih uporabljajo različne strategije. Pri bakteriji Escherichia coli (E. coli) poškodbe DNA, povzročene z antibiotiki, kot sta trimetoprim (TMP) in mitomicin C (MMC), sprožijo odziv SOS, ki aktivira gen tisB. Protein TisB je majhen toksin, ki poškoduje celično membrano in zmanjša protonsko gibalno silo (PMF), kar vpliva na preživetje bakterij in njihov odziv na okolico. V tej magistrski nalogi smo preučevali, kako TisB vpliva na preživetje E. coli po izpostavitvi TMP ali MMC, njegovo vlogo pri zaščiti pred kolicinom E7 in njegov vpliv na okužbo z bakteriofagom T4. Seva divji tip (WT) in ∆tisB smo primerjali prek merjenja preživetja po izpostavitvi različnim koncentracijam MMC ali TMP, stopnje depolarizacije membrane in preživetja v okoljih s sevom BZB2110, ki proizvaja kolicin E7. Rezultati nakazujejo, da depolarizacija, povzročena s TisB, vpliva na preživetje na način, ki je odvisen od antibiotika, in lahko bodisi nudi zaščito pred kolicinom E7 z zmanjšanjem transporta preko membrane bodisi prepreči vnos hranil, potrebnih za preživetje. Nadalje smo preučevali vpliv proteina TisB na okužbo z bakteriofagom T4 z merjenjem brstnega števila z in brez predhodne sprožitve odziva SOS, pri čemer je imel sev ∆tisB višje brstno število v primerjavi z WT. Vendar pa je ta razlika lahko posledica drugih dejavnikov in ne nujno zmanjšanega vstopa virusa v depolarizirane celice seva WT. Dobljeni rezultati omogočajo boljše razumevanje bakterijskih obrambnih sistemov in njihove vloge pri preživetju v kompetitivnih okoljih. toxin-antitoxin systems colicins Escherichia coli SOS response bacteriophage T4 survival frequency toksin-antitoksin sistemi kolicini Escherichia coli SOS odziv bakteriofag T4 pogostost preživetja true false false [L. Brezovnik] Angleški jezik Slovenski jezik Magistrsko delo/naloga 2025-09-21 07:16:57 2025-09-21 07:17:03 2025-10-11 04:01:31 0000-00-00 00:00:00 2025 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 579.26:578.2:615.33 265252 249734915 51411.pdf 51411.pdf 1 AB69181AF769609710CA03E5C50B0B57 60447fd4042419188ccc756cf5bd691321faed160c40fabae62d4600749211a8 06f4b2ac-96aa-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=218394 Biotehniška fakulteta 0 0 0