Grant: Travel Awards - Institute Community Support

Bacteria may look simple, but even within a single species, individual cells can behave differently. We found that many bacteria use a special trick-called phase variation-to quickly and reversibly switch parts of their DNA on and off. This lets a single bacterial strain split into several slightly different "versions" of itself. We call these groups "quasi-clones," because they're almost identical but not quite. Using a new ultra-high-throughput technology that reads the DNA of tens of thousands of individual bacterial cells, we were able to track how these quasi-clones form and change over time. We discovered that bacteria don't generate this variation randomly. Instead, they produce the same sets of quasi-clones in a highly organized and repeatable way. When we studied a common human gut bacterium in mice, we found that different quasi-clones become more or less common depending on whether the gut is healthy or inflamed during infection. This suggests that each quasi-clone may have a different role in helping bacteria adapt to changing conditions. We also found signs that this strategy is used by nearly all bacteria that live on or inside humans, meaning most bacteria likely exist as these coordinated, mixed populations rather than as one uniform group. Overall, our work changes how we think about both harmful and beneficial microbes-showing that they survive, thrive, and interact with us not as identical cells, but as flexible teams of slightly different versions of themselves.