| Summary: | MmpL (mycobacterial membrane protein large) proteins are integral membrane proteins that have been implicated in the biosynthesis and/or transport of mycobacterial cell wall lipids. Given the cellular location of these proteins, however, it is unclear how cell wall lipids are transported beyond the inner membrane. Moreover, given that mycobacteria grow at the poles, we also do not understand how new cell wall is added in a highly localized and presumably coordinated manner. Here, we examine the relationship between two lipid transport pathways associated with the proteins MmpL11 and LprG−Rv1410c. The lipoprotein LprG has been shown to interact with proteins involved in cell wall processes including MmpL11, which is required in biofilms for the surface localization of certain lipids. Here we report that deletion of <i>mmpL11</i> (<i>MSMEG_0241</i>) or the <i>lprG−rv1410c</i> operon homologues <i>MSMEG_3070−3069</i> in <i>Mycobacterium smegmatis</i> produced similar biofilm defects that were distinct from that of the previously reported <i>mmpL11</i> transposon insertion mutant. Analysis of pellicle biofilms, bacterial growth, lipid profiles, and gene expression revealed that the biofilm phenotypes could not be directly explained by changes in the synthesis or localization of biofilm-related lipids or the expression of biofilm-related genes. Instead, the shared biofilm phenotype between Δ<i>MSMEG_3070−3069</i> and Δ<i>mmpL11</i> may be related to their modest growth defect, while the origins of the distinct <i>mmpL11::Tn</i> biofilm defect remain unclear. Our findings suggest that the mechanisms that drive pellicle biofilm formation in <i>M. smegmatis</i> are not connected to crosstalk between the LprG−Rv1410c and MmpL11 pathways and that any functional interaction between these proteins does not relate directly to their lipid transport function.
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