Surface hydrolysis of sphingomyelin by the outer membrane protein R v0888 supports replication of M ycobacterium tuberculosis in macrophages

Summary Sphingomyelinases secreted by pathogenic bacteria play important roles in host–pathogen interactions ranging from interfering with phagocytosis and oxidative burst to iron acquisition. This study shows that the M tb protein R v0888 possesses potent sphingomyelinase activity cleaving sphingomyelin, a major lipid in eukaryotic cells, into ceramide and phosphocholine, which are then utilized by M tb as carbon, nitrogen and phosphorus sources, respectively. An M tb rv0888 deletion mutant did not grow on sphingomyelin as a sole carbon source anymore and replicated poorly in macrophages indicating that M tb utilizes sphingomyelin during infection. R v0888 is an unusual membrane protein with a surface‐exposed C ‐terminal sphingomyelinase domain and a putative N ‐terminal channel domain that mediated glucose and phosphocholine uptake across the outer membrane in an M . smegmatis porin mutant. Hence, we propose to name R v0888 as SpmT ( sp hingomyelinase of M ycobacterium t uberculosis ). Erythrocyte membranes contain up to 27% sphingomyelin. The finding that R v0888 accounts for half of M tb's hemolytic activity is consistent with its sphingomyelinase activity and the observation that R v0888 levels are increased in the presence of erythrocytes and sphingomyelin by 5‐ and 100‐fold, respectively. Thus, R v0888 is a novel outer membrane protein that enables M tb to utilize sphingomyelin as a source of several essential nutrients during intracellular growth.