TheaceEinvolves in mycolic acid synthesis and biofilm formation inMycobacterium smegmatis

Background The integrity of cell wall structure is highly significant for the in vivo survival of mycobacteria. We hypothesized that changes in morphology may indicate changes in cell wall metabolism and identified anaceEgene mutant (aceE-mut) which presented a deficient colony morphology on 7H10 agar by screening transposon mutagenesis inMycolicibacterium smegmatis, basonymMycobacterium smegmatis(M. smegmatis). This study aimed to identify the functional role ofaceEgene in cell wall biosynthesis inM. smegmatis. Results We observed that the colony morphology ofaceE-mut was quite different, smaller and smoother on the solid culture medium than the wild-type (WT) strain during the transposon library screening ofM. smegmatis. Notably, in contrast with the WT, which aggregates and forms biofilm, theaceE-mut lost its ability of growing aggregately and biofilm formation, which are two very important features of mycobacteria. The morphological changes in theaceE-mut strain were further confirmed by electron microscopy which indicated smoother and thinner cell envelope images in contrast with the rough morphology of WT strains. Additionally, theaceE-mut was more fragile to acidic stress and exhibited a pronounced defects in entering the macrophages as compared to the WT. The analysis of mycolic acid (MA) using LC-MS indicated deficiency of alpha-MA and epoxy-MA inaceE-mut strain whereas complementation of theaceE-mut with a wild-typeaceEgene restored the composition of MA. Conclusions Over all, this study indicates thataceEgene plays a significant role in the mycolic acid synthesis and affects the colony morphology, biofilm formation ofM. smegmatisand bacteria invasion of macrophage.