The rod-shaped tuberculosis (TB) bacterium, which the World Health Organization has once again ranked as the top infectious disease killer globally, is the first single-celled organism ever observed to maintain a consistent growth rate throughout its life cycle. These findings, reported by Tufts University School of Medicine researchers on November 15 in the journal Nature Microbiology, overturn core beliefs of bacterial cell biology and hint at why the deadly pathogen so readily outmaneuvers our immune system and antibiotics.

The most basic thing you can study in bacteria is how they grow and divide, yet our study reveals that the TB pathogen is playing by a completely different set of rules compared to easier-to-study model organisms.

These experiments showed that the TB bacterium doesn’t follow expected patterns of cell growth. In other bacterial species, growth is exponential, which means cells grow slower when they are smaller. For TB bacteria, growth rates can be the same whether they are newly born (and small) or far along in their cell cycle and soon to divide.