Novel Cyanobacterial Toxin-Antitoxin Systems

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Bacterial toxin-antitoxin (TA) systems are known as genetic elements, which are encoded by plasmid as well as chromosomal loci and mediate plasmid and genomic island maintenance through post-segregational killing mechanisms. However, TA systems exist in surprisingly high numbers in all pro-karyotes and a growing number of publications suggest TA systems with milder effects to act as mobile stress response systems which help certain cells of a population in persisting adverse growth conditions. TA systems can trigger cell cycle arrest as well as programmed cell death; accordingly, DNA replication and metabolism, translation and cell membrane organization are among their verified cellular targets. In cyanobacteria, oxygenic photosynthesis and thylakoid membranes appear as at-tractive additional targets, but not a single cyanobacterial TA system has been experimentally charac-terized so far. This is in contrast to the results of our own initial analyses, which point to a high number of TA cassettes controlled by peptide antitoxins or antisense RNA. This proposal aims at the molecular characterization of seven putative cyanobacterial TA systems. Among our objectives is the characterization of their control, regulation and mode of action, to understand how cells sense and cope with these factors and how the respective developmental and stress response programs are triggered. The results will have implications for the application of TA systems as natural resistance markers in biotechnology, the development of novel substances with antibiotic properties and are fundamentally relevant to understand how bacteria can survive adverse conditions.