Functional analysis of serine acetyltransferase from Mycobacterium smegmatis

Serine acetyltransferase (CysE) is involved in L-cysteine biosynthesis in Mycobacterium, and it is important for the self-defense mechanism of the bacteria. Mycobacterium tuberculosis CysE (Rv2335) has been identified as a serine acetyltransferase, and it is orthologous to Mycobacterium smegmatis MSMEG_5947. In this study, the MSMEG_5947 gene was cloned, expressed, and identified as a serine acetyltransferase. To investigate the function of M. smegmatis CysE, a MSMEG_5947 knockout mutant strain (M. sm-ΔM_5947) was generated through homologous recombination. The growth and morphological characteristics of this strain were studied using growth curves and electron microscopy, respectively. M. sm-ΔM_5947 grew slower than M. smegmatis mc(2) 155. Electron microscopy revealed that the lack of the M. smegmatis CysE protein caused drastic morphological changes. Therefore, deletion of the serine acetyltransferase retards the growth of the Mycobacterium, but serine acetyltransferase expression is not essential for the survival of the bacteria.