The bifunctional protein GlmU is a key factor in biofilm formation induced by alkylating stress in Mycobacterium smegmatis

Living organisms have developed specific defence mechanisms to counteract hostile environmental conditions. Alkylation stress response mechanisms also occur in Mycobacterium tuberculosis (MTB) the pathogen responsible for tuberculosis. The effect of alkylating agents on the cellular growth of MTB was investigated using methyl methanesulfonate (MMS) as methyl donor demonstrating that limited doses of alkylating agents might affect MTB cell viability. A global investigation of M. smegmatis response to alkylating stress was then pursued by differential proteomics to identify the most affected cellular pathways. Quantitative analysis of proteomic profiles demonstrated that most of the proteins upregulated in the presence of alkylating agents are involved in biofilm formation and/or cell wall biosynthesis. Tailored experiments confirmed that under stress conditions M. smegmatis elicits physical defence mechanisms by increasing biofilm formation. Among the upregulated proteins, we identified the GlmU bifunctional enzyme as a possible factor involved in biofilm production. Experiments with both conditional deletion and overexpressing glmU mutants demonstrated that down regulation of GlmU decreased M. smegmatis capabilities to produce biofilm whereas overexpression of the enzyme increased biofilm formation. These results were supported by inhibition of GlmU acetyltransferase activity with two different inhibitors, suggesting the involvment of this enzyme in the M. smegmatis defence mechanisms.