Bacteria grow in one of three mutually exclusive ways: Depending on the species, they either grow by dividing at a midpoint, grow laterally at the sides of the cell, or grow vertically at the tips of the cell.  

Or so we thought.  

In a new study led by Marie Elliot, professor and Chair of McMaster’s Department of Biology, researchers found that the bacteria Streptomyces venezuelae can actually grow from both its sides and its tips.  

This never-before-seen behaviour, detailed recently in the journal Nature Microbiology, fundamentally changes conventional understandings of how some bacteria grow and multiply.  

“It really demonstrates that the bacterial cell wall is far more flexible and complex than we had previously appreciated or understood,” says Elliot, a member of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster.  

The cell wall is a hardy outside layer that gives bacteria their structure, their shape, and protection from the outside world. It’s also vital for growth, as the cell wall must expand for bacteria to get bigger or multiply — regardless of which growth process they employ.   

Elliot, who is also an associate member of the Department of Biochemistry and Biomedical Sciences, says that the bacterial cell wall is major drug target.  

The antibiotic penicillin, for example, functions specifically by weakening the cell wall — so research like this may have implications for how we approach the treatment of bacterial infections.  

“This research shows that there are potentially alternative ways to go about tackling the bacterial cell wall,” she says.  

“If you have one drug that targets conventional growth mechanisms, and another that at the same time inhibits these secondary systems, we may end up with a more potent way of attacking these organisms.” 

The new discovery was documented during a process called “exploratory growth,” where Streptomyces — which is a typically stationary bacteria — can suddenly take off, grow exponentially, and colonize nearby surfaces.  

Matthew Zambri, a postdoctoral fellow in Elliot’s lab and first author on the new paper, was investigating how and why this process occurs when he observed in real-time that the bacteria was growing in multiple different ways.   

Zambri says that the different forms of bacterial cell wall growth are directed by distinct proteins, and that it’s long been considered unusual that two of these different proteins are found in Streptomyces; however, until now, prevailing hypotheses tied the presence of lateral growth proteins to spores — not to growth.    

“These new findings speak to all of the unknowns that still exist about how bacteria grow,” Zambri says. “Already, we have learned that this phenomenon is more widespread within actinobacteria than previously thought. And if it can happen in one type of bacteria, then it’s certainly possible that it can happen in others as well.”