A sigma (σ) factor is a constituent of bacterial RNA polymerase that guides the holoenzyme to promoter sequences and initiates transcription. In addition to a primary housekeeping σ factor, bacteria contain a number of alternative σ factors which recognize a specific set of promoters. By replacing the primary σ factor with alternative variants, the cell controls transcription of the whole sets of genes, typically to acclimate to changes in the environment. As key regulatory elements, σ factors are frequent targets of genetic manipulation aimed at the improvement of bacterial stress tolerance and capacity for bioproduction. Cyanobacteria are a phylum of bacteria capable of oxygenic photosynthesis and there is a great interest to employ them as biochemical and biofuel production hosts. Engineering of σ factor genes has become an important strategy to improve robustness and suitability of cyanobacteria for the production of high-value metabolites such as polyhydroxybutyrate, succinate, sucrose or hydrogen. Here, we summarize the current knowledge about the regulatory role of different σ factor classes in cyanobacteria, highlighting their biotechnological potential.

Centre Algatech Institute of Microbiology of the Czech Academy of Sciences Třeboň 37981 Czech Republic

Centre Algatech Institute of Microbiology of the Czech Academy of Sciences Třeboň 37981 Czech Republic; Faculty of Science University of South Bohemia České Budějovice 37001 Czech Republic

Department of Biology California State University Northridge 18111 Nordhoff Street Northridge CA 91330 8303 USA

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