Tumebacillus is a genus of Gram-positive, rod-shaped, spore-forming bacteria. Members of the genus can be motile or non-motile, and form white or yellow colonies on R2A agar. The genus was first proposed in 2008 from the discovery of a potentially 5000-7000 year-old bacterium from Canadian high arctic permafrost, which would become the type strain of the genus T. permanentifrigoris. The genus name was derived from Latin tume (from tumefacere, to make swollen) and bacillus (small rod), referring to the swollen sporangia produced by T. permanentifrigoris and the shape of the cells.