en Other Other Original article Original article <div dir="ltr"><strong><span style="font-family:garamond,serif;"><span style="font-size:10.0pt;">Introduction: </span></span></strong><span style="font-family:garamond,serif;"><span style="font-size:10.0pt;">Bacteria have at least one sigma factor (&sigma;-factor) that transcribes the genes required for cell viability. Usually, transcription of &sigma;-factors occurs and changes in response to a variety of environmental stresses. Expression of &sigma;-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 &sigma;-factors genes including &sigma;^A, &sigma;^B, &sigma;^D, &sigma;^E, &sigma;^F, &sigma;^G, &sigma;^H, &sigma;^J, &sigma;^K, &sigma;^L, and &sigma;^M on morphology, growth pattern and biofilm formation in <em>Mycobacterium marinum</em> CCUG 20998. <strong>Methods</strong>: In this study, the genes for major &sigma;-factors were cloned in the expression vector pAGHD1, containing 11 kb <em>Hind III</em> fragment of pAG1 and Tetz determinants. A quantitative real-time PCR (qRT-PCR) assay was used to quantify &sigma;-factor mRNA levels of &sigma;-factors in exponential and stationary phases. The overexpression in real-time experiments was normalized to the &sigma;^A expression level. The effect of expression was evaluated on biofilm formation in this bacterium. <strong>Results:</strong> Some selected &sigma;-factors used in this study were overexpressed. The &sigma;^Bhad the highest expression level during the exponential and stationary phases. The &sigma;-factors &sigma;^D, &sigma;^G, and &sigma;^H showed lower expression level compared with &sigma;^E, &sigma;^F, and &sigma;^K. The lowest expression belonged to &sigma;^L and &sigma;^M &sigma;-factors. Also, overexpression of &sigma;^E and &sigma;^K led to more biofilm formation in comparison to other &sigma;-factors in <em>M. marinum</em> CCUG 20998. <strong>Conclusion:</strong> The overexpression of some &sigma;-factors can affect growth, morphology and biofilm formation in <em>M. marinum </em>CCUG 20998.</span></span></div> Mycobacterium marinum CCUG 20998, Overexpression, Sigma Factors, Biofilm 68 75 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-128-1&slc_lang=en&sid=1 Mohammad Faezi Ghasemi faezi_m@yahoo.com Yes Department of Microbiology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran Fatemeh Alikhani elham.alikhani.ea@gmail.com No Department of Microbiology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran