Bacteria have at least one sigma factor (σ-factor) that transcribes the genes required for cell viability. Usually, transcription of σ-factors occurs and changes in response to a variety of environmental stresses. Expression of σ-factors is one of the strategies which is used in response to different stress conditions. This study was aimed to evaluate the effects of overexpression of σ-factors genes including σA, σB, σD, σE, σF, σG, σH, σJ, σK, σL, and σM on morphology, growth pattern and

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... m formation in Mycobacterium marinum CCUG 20998. Methods: In this study, the genes for major σ-factors were cloned in the expression vector pAGHD1, containing 11 kb Hind III fragment of pAG1 and Tetz determinants. A quantitative real-time PCR (qRT-PCR) assay was used to quantify σ-factor mRNA levels of σ-factors in exponential and stationary phases. The overexpression in real-time experiments was normalized to the σA expression level. The effect of expression was evaluated on biofilm formation in this bacterium. Results: Some selected σ-factors used in this study were overexpressed. The σB had the highest expression level during the exponential and stationary phases. The σ-factors σD, σG, and σH showed lower expression level compared with σE, σF, and σK. The lowest expression belonged to σL and σM σ-factors. Also, overexpression of σE and σK led to more biofilm formation in comparison to other σ-factors in M. marinum CCUG 20998. Conclusion: The overexpression of some σ-factors can affect growth, morphology and biofilm formation in M. marinum CCUG 20998.