Metabolic profile of Mycobacterium smegmatis reveals Mce4 proteins are relevant for cell wall lipid homeostasis

Introduction The Mce proteins are encoded in a variable number of operons (from one to eight) in all Mycobacterium species. A role in the transport of host and mycobacterial lipids has been demonstrated for some Mce proteins in the pathogen Mycobacterium tuberculosis but little is known about these proteins in Mycobacterium smegmatis, a soil dweller species.Objective To investigate the role of Mce proteins in M. smegmatis.Method We used a non-targeted GC-MS approach to define the metabolic profiles of knockout mutants in mce operons of M. smegmatis. Metabolomic analysis was complemented with thin layer chromatography and transcriptional studies.Result We demonstrated that the lack of Mce4 proteins alters the primary carbon metabolism of M. smegmatis by reducing the content of fatty acids and increasing the accumulation of two stress-related compounds, glutamate/glutamine and triacyl glycerol (TAG). We also provide evidence supporting that the accumulation of TAG in a Δmce4 mutant depends on the bacterial redox state.Conclusion These results, together with the finding that the cell surface of the Delta mce4 mutant is significantly altered, support a role for Mce4 in maintaining the cell wall lipids architecture of M. smegmatis, which, when altered, induces a redox imbalance that results in the accumulation of the stress-related compounds.