Microbial communities are shaped by species interactions that often work through changes to their shared environment—depleting nutrients, shifting pH, or releasing chemicals. But these environmental changes may last. If yesterday’s microbes alter the environment through interactions, today’s species don’t start from a clean slate. Yet most community models and experiments treat interactions as if they happen in a static environment and ignore history. This research asked whether these lasting, environment-mediated changes act as an external, collective “memory” that influences which microbes grow or fail later. Showing when and how such memory forms matters for making microbial behavior more predictable and for steering communities—for example, in the gut, soils, or fermentation—because the same species mix could end up in different stable states depending on the path taken.
Changes to the environment can create a kind of “memory” in microbial ecosystems that strongly alters interaction outcomes and community assembly. This memory is stored as chemical modifications of the environment and does not reside inside individual cells. Importantly, it requires the combined activity of many bacteria to build up—making it a collective phenomenon. Under these conditions, past growth factors such as temperature or oxygen levels can reshape future interactions. Entire communities may even assemble into different stable states from the same initial species mix, depending on this externalized memory. The results show further that memory storage does not need complex cell physiology—it can emerge in simple systems. This highlights that to understand and predict community assembly, a system’s history must be accounted for. A straightforward mechanism developed in this research can explain widely observed memory effects in ecosystems.
The findings reveal that microbial communities can “remember” past conditions through persistent changes in their environment. This shows that interactions depend not only on which species are present, but also on their history. For scientists, it provides a simple, testable mechanism to explain why communities with the same species mix can develop differently depending on their past—helping to make models of microbial community dynamics more realistic and predictive. For wider society, this understanding can guide better management of microbial communities, from restoring healthy gut microbiomes to improving soil health or fermentation processes. Recognizing and accounting for such memory effects is essential when aiming to guide or manipulate microbial communities toward desired outcomes.
Read the full journal article titled ‘Environment-mediated interactions cause an externalized and collective memory in bacteria‘ in The ISME Journal. This article has been selected as Editor’s Choice for the month of August 2025.
Authors
- Shubham Gajrani, University of Tuebingen, Germany
- Xiaozhou Ye, University of Tuebingen, Germany
- Christoph Ratzke, University of Tuebingen, Germany