Impact of the deletion of the six mce operons in Mycobacterium smegmatis

Abstract

The Mycobacterium smegmatis genome contains six operons designated mce (mammalian cell entry). These operons, which encode membrane and exported proteins, are highly conserved in pathogenic and non-pathogenic mycobacteria. Although the function of the Mce protein family has not yet been established in Mycobacterium smegmatis, the requirement of the mce4 operon for cholesterol utilization and uptake by Mycobacterium tuberculosis has recently been demonstrated. In this study, we report the construction of an M. smegmatis knock-out mutant deficient in the expression of all six mce operons. The consequences of these mutations were studied by analyzing physiological parameters and phenotypic traits. Differences in colony morphology, biofilm formation and aggregation in liquid cultures were observed, indicating that mce operons of M. smegmatis are implicated in the maintenance of the surface properties of the cell. Importantly, the mutant strain showed reduced cholesterol uptake when compared to the parental strain. Further cholesterol uptake studies using single mce mutant strains showed that the mutation of operon mce4 was reponsible for the cholesterol uptake failure detected in the sextuple mce mutant. This finding demonstrates that mce4 operon is involved in cholesterol transport in M. smegmatis.

Label-free Quantitative Proteomics Reveals a Role for the Mycobacterium tuberculosis SecA2 Pathway in Exporting Solute Binding Proteins and Mce Transporters to the Cell Wall*

“…The specific function of Mce1 during infection is not clear, but a potential role of Mce1 in importing free mycolic acids was recently proposed (57,84). Mce4 is the best studied Mce transporter, with a shown role in cholesterol import (85,86) and a role in virulence (85,87). Thus, another way that the SecA2 pathway may contribute to M. tuberculosis infection could be through its role in SBP and Mce transporter localization.…”

The mycobacterial P55 efflux pump is required for optimal growth on cholesterol

“…strain RHA1, a soil bacterium related to M. tuberculosis, revealed that 51 rhodococcal genes specifically expressed during growth on cholesterol were conserved within an 82-gene cluster in M. tuberculosis H37Rv and Mycobacterium bovis bacillus Calmette-Guerin (BCG). 2 These studies provided the first indication of a cholesterol catabolic pathway critical for intracellular survival, and led to the identification of the Mce4 system, a multi-subunit ABC-like transporter functioning in cholesterol uptake by Rhodococcus, 3 Mycobacterium smegmatis 4 and M. tuberculosis. 5 The Mce4 transporter is essential for survival during the chronic stages of infection.…”

Lipid Inclusions in Mycobacterial Infections

“…In 2008 Pandey and Sassetti found that M. tuberculosis can grow using cholesterol as a primary carbon source and that the mce4 transporter is required for cholesterol uptake. M. tuberculosis contains four homologous mce operons, mce1-mce4, which are thought to encode lipid transporters [57,58].…”