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To survive in a constantly changing environment, bacteria need to adapt their lifestyle. They need mechanisms to regulate their growth rate, both in response to nutrient availability, but also to protect themselves against toxic compounds, including antibiotics. Bacteria can express a toxin, which trigger reduced growth, but also an antitoxin to avoid inadvertent toxin expression in conditions that favor growth. A newly discovered toxin-antitoxin system has been identified in Salmonella. The transcription of the toxin, TimP, is repressed by an antitoxin, TimR, and regulatory factors of these were investigated in this study.

Reporter gene fusions were constructed, and these were used together with transposon mutagenesis, where a transposon was randomly inserted in the Salmonella genome. This was done to investigate genes that affect transcription of timP and timR. No transposon insertion resulting in altered fluorescence level, meaning altered transcription, could be detected for timP mRNA. For TimR several insertions resulted in increased fluorescence level. A general trend of the knocked-out genes resulting in increased fluorescence, were that many could be linked to membrane activity. Two of the identified genes were previously known transcription factors, EmrR and SlyA, both known to bind to AT-rich sequences. The promoter regions of TimP and TimR are AT-rich and therefore a direct interaction with these transcription factors is possible. Further studies are needed to confirm the obtained result and with more knowledge, hopefully the function of this and other toxin-antitoxin systems will be understood.