smegmatis

Mycobacterium smegmatis, commonly referred to as M. smegmatis, is a nonpathogenic, fast-growing species of the genus Mycobacterium. It is an environmental bacterium found in soil and water and is widely used as a model organism for mycobacterial biology because its growth and genetics are more tractable than those of pathogenic relatives.

In the laboratory, M. smegmatis grows on standard mycobacterial media such as Middlebrook 7H9 or 7H10. Under favorable conditions it forms colonies within about two to five days, and its doubling time is typically around three hours, making it one of the fastest-growing mycobacteria. Like other members of the genus, it has a waxy cell envelope rich in mycolic acids, contributing to distinctive colony morphology and environmental resilience.

The genome of M. smegmatis is approximately 6 megabases in size with a high GC content around 65–67%, encoding roughly 5,000 to 6,000 genes. The MC^2 155 strain is a commonly used laboratory variant that has facilitated genetic studies and tool development in mycobacteria.

As a model organism, M. smegmatis is employed to develop and test genetic tools for mycobacteria, including replicating and integrating plasmids, transposon mutagenesis, and phage-based transduction. It serves to study cell wall biogenesis, secretion systems, metabolism, and antibiotic susceptibility, providing a safer and faster platform for preliminary research before work with pathogenic species. It is handled at biosafety level 2, reflecting its nonpathogenic status while requiring standard mycobacterial safety practices.