Escherichia coli is arguably the best-studied organism on Earth, and for decades, whatever scientists learned about it tended to get generalized across the bacterial kingdom. One of the field’s foundational assumptions was straightforward: bacteria allocate their resources to grow as fast as their environment allows, full stop. Now, researchers at the University of California San Diego have shown that assumption doesn’t hold universally, and the exception comes from an organism as mundane as dirt.
Bacillus subtilis, a bacterium commonly found in soil, turns out to follow a fundamentally different survival strategy than its intestinal cousin, according to work published in the journal Science. Where E. coli races to multiply even under adverse conditions, on the theory that more bacteria means better odds some will survive, B. subtilis does something closer to the opposite: it deliberately throttles its own growth to improve its chances of riding out stress.
The discovery began, as these things often do, with an experiment that didn’t go as planned. A decade ago, researchers in UC San Diego physics professor Suckjoon Jun’s lab set out to reproduce a well-established E. coli finding in B. subtilis. In E. coli, when an antibiotic partially blocks protein production, the cell compensates by building even more ribosomes, the molecular machinery that manufactures proteins. Jun’s team expected B. subtilis to respond the same way. Instead, its ribosome levels stayed essentially flat.
Jun initially assumed the experiment had simply gone wrong. But the result held up across repeated trials, forcing him to conclude that B. subtilis was managing cellular stress through an entirely different mechanism than the one seen in E. coli.
To dig deeper, Jun brought in Jade Wang, a professor of bacteriology at the University of Wisconsin-Madison who studies the bacterial stringent response, the survival mechanism organisms use to cope with harsh conditions like nutrient scarcity or antibiotic exposure. The collaboration revealed that the two bacterial species rely on distinct internal control systems to manage the same basic problem. As Jun described it, bacteria are generally thought to grow as fast as available nutrients allow by carefully balancing resource investment, but under antibiotic stress, B. subtilis does the opposite, deliberately holding its growth below its own capacity.
The mechanics come down to how each organism balances its cellular budget between ribosomes, which build proteins, and the rest of the cell’s machinery, which manufactures the raw materials, like amino acids, those ribosomes need. In E. coli, a small signaling molecule called (p)ppGpp functions like a control switch: when amino acid supplies run low, the molecule’s levels rise and instruct the cell to build fewer ribosomes, keeping supply and demand in sync.
B. subtilis relies on a different switch entirely: guanosine triphosphate, or GTP, which does double duty as both an energy source for core cellular processes and a regulatory signal for stress responses. Under adverse conditions, GTP levels in B. subtilis fall, which slows amino acid production, but ribosome levels stay constant. The result is a kind of decoupling, where the cell’s manufacturing floor remains fully staffed even as the supply of raw materials dwindles.
That mismatch turns out to be the point. Keeping ribosome counts steady even as GTP drops slows the bacterium’s growth, but it also makes the cell more tolerant of stress. When GTP levels are high, growth speeds up, but the cells become more vulnerable. The trade-off effectively lets B. subtilis choose, depending on conditions, between growing faster or hunkering down to survive.
In head-to-head lab tests, B. subtilis substantially outperformed E. coli at surviving antibiotic exposure. The researchers suspect this connects to a phenomenon called persistence, in which a small subset of cells rides out antibiotic exposure without acquiring genetic resistance, then resumes normal growth once conditions improve.
Jun said the finding upended a basic expectation about how bacteria behave. Researchers tend to assume organisms are built to grow as fast as possible, he said, but this one chooses not to: it holds itself back to stay alive under stress, and when the team experimentally flipped the switch controlling that decision, the bacterium grew faster but became far more vulnerable. He described it as a constant gamble the cell runs between growing and surviving, one that may help explain why bacteria in general are so difficult to eliminate.
The work challenges the long-standing assumption that bacteria are simply wired to grow as quickly as possible, suggesting instead that many organisms actively balance growth against survival as a deliberate strategy. Because the growth slowdown in B. subtilis is directly tied to its ability to survive antibiotics, the findings open a new angle for thinking about how bacteria more broadly tolerate drug treatment.
The study, “Decoupling of global metabolic flux and proteome partitioning in bacteria,” involved researchers from UC San Diego, the University of Wisconsin-Madison, and Scripps Research, and was funded by the National Science Foundation, the National Institutes of Health, and the Simons Foundation.
Notes
1. University of California San Diego, news release, “A subtle difference offers insight into bacteria survival strategies,” published July 2, 2026, via EurekAlert.
2. Study: “Decoupling of global metabolic flux and proteome partitioning in bacteria,” Science (2026), DOI: 10.1126/science.aeb6410.
IMAGE CREDIT: NASA.