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.

σ（σ）因子是细菌RNA聚合酶的组成部分，可将全酶引导至启动子序列并启动转录。除了主要的管家σ因子外，细菌还包含许多其他σ因子，它们可以识别一组特定的启动子。通过用替代变体替代主要的σ因子，细胞可以控制整个基因集的转录，通常适应环境的变化。作为关键的调控元件，σ因子是遗传操纵的常见目标，旨在提高细菌的胁迫耐受性和生物生产能力。蓝细菌是能够进行氧光合作用的细菌的门类，并且非常有兴趣将其用作生化和生物燃料生产宿主。σ因子基因的工程化已成为提高蓝细菌的健壮性和适用性的重要策略，该蓝藻可用于生产高价值的代谢产物，例如聚羟基丁酸酯，琥珀酸酯，蔗糖或氢。在这里，我们总结了有关不同σ因子类在蓝细菌中的调控作用的当前知识，突出了它们的生物技术潜力。