Mycobacterium marinum Degrades Both Triacylglycerols and Phospholipids from Its Dictyostelium Host to Synthesise Its Own Triacylglycerols and Generate Lipid Inclusions

Abstract

During a tuberculosis infection and inside lipid-laden foamy macrophages, fatty acids (FAs) and sterols are the major energy and carbon source for Mycobacterium tuberculosis. Mycobacteria can be found both inside a vacuole and the cytosol, but how this impacts their access to lipids is not well appreciated. Lipid droplets (LDs) store FAs in form of triacylglycerols (TAGs) and are energy reservoirs of prokaryotes and eukaryotes. Using the Dictyostelium discoideum/Mycobacterium marinum infection model we showed that M. marinum accesses host LDs to build up its own intracytosolic lipid inclusions (ILIs). Here, we show that host LDs aggregate at regions of the bacteria that become exposed to the cytosol, and appear to coalesce on their hydrophobic surface leading to a transfer of diacylglycerol O-acyltransferase 2 (Dgat2)-GFP onto the bacteria. Dictyostelium knockout mutants for both Dgat enzymes are unable to generate LDs. Instead, the excess of exogenous FAs is esterified predominantly into phospholipids, inducing uncontrolled proliferation of the endoplasmic reticulum (ER). Strikingly, in absence of host LDs, M. marinum alternatively exploits these phospholipids, resulting in rapid reversal of ER-proliferation. In addition, the bacteria are unable to restrict their acquisition of lipids from the dgat1&2 double knockout leading to vast accumulation of ILIs. Recent data indicate that the presence of ILIs is one of the characteristics of dormant mycobacteria. During Dictyostelium infection, ILI formation in M. marinum is not accompanied by a significant change in intracellular growth and a reduction in metabolic activity, thus providing evidence that storage of neutral lipids does not necessarily induce dormancy.

Time-resolved RNA-seq profiling of the infection of Dictyostelium discoideum by Mycobacterium marinum reveals an integrated host response to damage and stress

“…Additionally, the late time points showed a clear downregulation of lytic enzymes and ATP hydrolysis-coupled proton transport and an upregulation of genes belonging to the TOR pathway (regulation of the intracellular signal transduction). Lipid metabolism (ceramide synthases) and transport (ABC transporters) seem to play a central role during the infection time-course as genes belonging to these groups were upregulated at various time points, which is in perfect agreement with the documented interface between the host and the pathogen lipid metabolisms (figure 7 E-G) (Barisch et al, 2015;Barisch and Soldati, 2017).…”

Proteomic characterization of theMycobacterium marinum-containing vacuole inDictyostelium discoideum

“…Oxysterol binding protein 7 could be important for the transfert of lipid from the lipid droplets to the MCV. PLC would allow M. marinum to use host phospholipids as previously proposed (Barisch and Soldati 2017). Interestingly, a small GTPase, Roco5, was found accumulated in the M. marinum-MCV at 6 hpi.…”

Structural basis of glycerophosphodiester recognition by theMycobacterium tuberculosissubstrate-binding protein UgpB

“…In addition, mannosylated phosphatidylinositol and phosphatidylethanolamine are constituents of the outer layer of the Mtb cell envelope. Given this scenario, it is possible that glycerophosphodiester metabolites are also derived through remodelling of Mtb cell envelope 33,34,36,39,40 . Further experiments are underway to elucidate the involvement of host and Mtb-derived lipids.…”